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PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

Page 2 of 90

JUNE 2004 Revision 1.04

LIFE SUPPORT POLICY

Pericom Semiconductor Corporation's products are not authorized for use as critical components in life support
devices or systems unless a specific written agreement pertaining to such intended use is executed between the
manufacturer and an officer of PSC.

1) Life support devices or system are devices or systems which:

a) Are intended for surgical implant into the body or
b) Support or sustain life and whose failure to perform, when properly used in accordance with

instructions for use provided in the labeling, can be reasonably expected to result in a significant injury
to the user.

2) A critical component is any component of a life support device or system whose failure to perform can be

reasonably expected to cause the failure of the life support device or system, or to affect its safety or
effectiveness. Pericom Semiconductor Corporation reserves the right to make changes to its products or
specifications at any time, without notice, in order to improve design or performance and to supply the best
possible product. Pericom Semiconductor does not assume any responsibility for use of any circuitry
described other than the circuitry embodied in a Pericom Semiconductor product. The Company makes no
representations that circuitry described herein is free from patent infringement or other rights of third parties
which may result from its use. No license is granted by implication or otherwise under any patent, patent
rights or other rights, of Pericom Semiconductor Corporation.

All other trademarks are of their respective companies.

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

Page 5 of 90

JUNE 2004 Revision 1.04

TABLE OF CONTENTS

SIGNAL DEFINITIONS.............................................................................................................................13

1.1

SIGNAL

TYPES....................................................................................................................................13

1.2

SIGNALS ..............................................................................................................................................13

1.2.1

PRIMARY BUS INTERFACE SIGNALS ...................................................................................13

1.2.2

SECONDARY BUS INTERFACE SIGNALS .............................................................................14

1.2.3

CLOCK SIGNALS ........................................................................................................................16

1.2.4

MISCELLANEOUS SIGNALS ....................................................................................................16

1.2.5

GENERAL PURPOSE I/O INTERFACE SIGNALS .................................................................17

1.2.6

POWER AND GROUND..............................................................................................................17

1.3

LIST

160-PIN

LFBGA.................................................................................................................18

PCI BUS OPERATION...............................................................................................................................19

2.1

TYPES

TRANSACTIONS ..............................................................................................................19

2.2

SINGLE

ADDRESS

PHASE.................................................................................................................20

2.3

DEVICE

SELECT

(DEVSEL#)

GENERATION ..................................................................................20

2.4

DATA

PHASE.......................................................................................................................................20

2.5

WRITE

TRANSACTIONS....................................................................................................................20

2.5.1

MEMORY WRITE TRANSACTIONS.........................................................................................21

2.5.2

MEMORY WRITE AND INVALIDATE .....................................................................................22

2.5.3

DELAYED WRITE TRANSACTIONS ........................................................................................22

2.5.4

WRITE TRANSACTION BOUNDARIES...................................................................................23

2.5.5

BUFFERING MULTIPLE WRITE TRANSACTIONS..............................................................23

2.5.6

FAST BACK-TO-BACK TRANSACTIONS ................................................................................23

2.6

READ

TRANSACTIONS .....................................................................................................................24

2.6.1

PREFETCHABLE READ TRANSACTIONS.............................................................................24

2.6.2

DYNAMIC PREFETCHING CONTROL....................................................................................24

2.6.3

NON-PREFETCHABLE READ TRANSACTIONS ...................................................................24

2.6.4

READ PREFETCH ADDRESS BOUNDARIES ........................................................................25

2.6.5

DELAYED READ REQUESTS ...................................................................................................25

2.6.6

DELAYED READ COMPLETION WITH TARGET .................................................................26

2.6.7

DELAYED READ COMPLETION ON INITIATOR BUS.........................................................26

2.6.8

FAST BACK-TO-BACK READ TRANSACTIONS ....................................................................27

2.7

CONFIGURATION

TRANSACTIONS................................................................................................27

2.7.1

TYPE 0 ACCESS TO PI7C8148A................................................................................................28

2.7.2

TYPE 1 TO TYPE 0 CONVERSION ...........................................................................................28

2.7.3

TYPE 1 TO TYPE 1 FORWARDING ..........................................................................................29

2.7.4

SPECIAL CYCLES.......................................................................................................................30

2.8

TRANSACTION

TERMINATION.......................................................................................................30

2.8.1

MASTER TERMINATION INITIATED BY PI7C8148A ..........................................................31

2.8.2

MASTER ABORT RECEIVED BY PI7C8148A .........................................................................32

2.8.3

TARGET TERMINATION RECEIVED BY PI7C8148A ...........................................................32

2.8.4

TARGET TERMINATION INITIATED BY PI7C8148A...........................................................34

ADDRESS DECODING..............................................................................................................................36

3.1

ADDRESS

RANGES ............................................................................................................................36

3.2

I/O

ADDRESS

DECODING..................................................................................................................36

3.2.1

I/O BASE AND LIMIT ADDRESS REGISTER .........................................................................37

3.2.2

ISA MODE ....................................................................................................................................37

3.3

MEMORY

ADDRESS

DECODING.....................................................................................................38

3.3.1

MEMORY-MAPPED I/O BASE AND LIMIT ADDRESS REGISTERS ..................................38

3.3.2

PREFETCHABLE MEMORY BASE AND LIMIT ADDRESS REGISTERS ..........................39

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

Page 6 of 90

JUNE 2004 Revision 1.04

3.4

VGA

SUPPORT ....................................................................................................................................40

3.4.1

VGA MODE ..................................................................................................................................40

3.4.2

VGA SNOOP MODE ....................................................................................................................40

TRANSACTION ORDERING ...................................................................................................................41

4.1

TRANSACTIONS

GOVERNED

ORDERING

RULES .................................................................41

4.2

GENERAL

ORDERING

GUIDELINES ...............................................................................................42

4.3

ORDERING

RULES .............................................................................................................................43

4.4

DATA

SYNCHRONIZATION .............................................................................................................44

ERROR HANDLING ..................................................................................................................................44

5.1

ADDRESS

PARITY

ERRORS..............................................................................................................44

5.2

DATA

PARITY

ERRORS.....................................................................................................................45

5.2.1

CONFIGURATION WRITE TRANSACTIONS TO CONFIGURATION SPACE ...................45

5.2.2

READ TRANSACTIONS .............................................................................................................45

5.2.3

DELAYED WRITE TRANSACTIONS ........................................................................................46

5.2.4

POSTED WRITE TRANSACTIONS ...........................................................................................48

5.3

DATA

PARITY

ERROR

REPORTING

SUMMARY...........................................................................49

5.4

SYSTEM

ERROR

(SERR#)

REPORTING ...........................................................................................52

PCI BUS ARBITRATION ..........................................................................................................................53

6.1

PRIMARY

PCI

BUS

ARBITRATION..................................................................................................53

6.2

SECONDARY

PCI

BUS

ARBITRATION............................................................................................53

6.2.1

PREEMPTION .............................................................................................................................53

6.2.2

BUS PARKING.............................................................................................................................54

CLOCKS ......................................................................................................................................................54

7.1

PRIMARY

CLOCK

INPUTS ................................................................................................................54

7.2

SECONDARY

CLOCK

OUTPUTS ......................................................................................................54

7.3

PCI

CLOCKRUN ..................................................................................................................................54

GENERAL PURPOSE I/O INTERFACE.................................................................................................55

8.1

GPIO

CONTROL

REGISTERS ............................................................................................................55

EEPROM INTERFACE .............................................................................................................................55

9.1

AUTO

MODE

EEPROM

ACCESS .......................................................................................................55

9.2

EEPROM

MODE

RESET................................................................................................................56

9.3

EEPROM

DATA

STRUCTURE ...........................................................................................................56

9.4

EEPROM

SPACE

ADDRESS

MAP......................................................................................................56

9.4.1

EEPROM CONTENT...................................................................................................................56

COMPACT PCI HOT SWAP.................................................................................................................58

PCI POWER MANAGEMENT .............................................................................................................58

RESET ......................................................................................................................................................59

12.1

PRIMARY

INTERFACE

RESET..........................................................................................................59

12.2

SECONDARY

INTERFACE

RESET ...................................................................................................59

12.3

CHIP

RESET .........................................................................................................................................60

SUPPORTED COMMANDS..................................................................................................................60

13.1

PRIMARY

INTERFACE ......................................................................................................................60

13.2

SECONDARY

INTERFACE ................................................................................................................61

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

Page 7 of 90

JUNE 2004 Revision 1.04

BRIDGE BEHAVIOR.............................................................................................................................62

14.1

BRIDGE

ACTIONS

FOR

VARIOUS

CYCLE

TYPES.........................................................................62

14.2

ABNORMAL

TERMINATION

(INITIATED

BRIDGE

MASTER) ..............................................63

14.2.1

MASTER ABORT.........................................................................................................................63

14.2.2

PARITY AND ERROR REPORTING .........................................................................................63

14.2.3

REPORTING PARITY ERRORS.................................................................................................63

14.2.4

SECONDARY IDSEL MAPPING................................................................................................63

CONFIGURATION REGISTERS.........................................................................................................64

15.1

TYPES ...............................................................................................................................64

15.2

CONFIGURATION

15.2.1

VENDOR ID REGISTER OFFSET 00h ..................................................................................65

15.2.2

DEVICE ID REGISTER OFFSET 00h....................................................................................65

15.2.3

COMMAND REGISTER OFFSET 04h ...................................................................................65

15.2.4

PRIMARY STATUS REGISTER OFFSET 04h ......................................................................66

15.2.5

REVISION ID REGISTER OFFSET 08h................................................................................67

15.2.6

CLASS CODE REGISTER OFFSET 08h................................................................................67

15.2.7

CACHE LINE REGISTER OFFSET 0Ch ...............................................................................67

15.2.8

PRIMARY LATENCY TIMER REGISTER OFFSET 0Ch.....................................................67

15.2.9

HEADER TYPE REGISTER OFFSET 0Ch ............................................................................67

15.2.10

PRIMARY BUS NUMBER REGISTER OFFSET 18h .......................................................67

15.2.11

SECONDARY BUS NUMBER REGISTER OFFSET 18h .................................................68

15.2.12

SUBORDINATE BUS NUMBER REGISTER OFFSET 18h .............................................68

15.2.13

SECONDARY LATENCY TIMER REGISTER OFFSET 18h ...........................................68

15.2.14

I/O BASE ADDRESS REGISTER OFFSET 1Ch................................................................68

15.2.15

I/O LIMIT ADDRESS REGISTER OFFSET 1Ch ..............................................................68

15.2.16

SECONDARY STATUS REGISTER OFFSET 1Ch............................................................69

15.2.17

MEMORY BASE ADDRESS REGISTER OFFSET 20h ....................................................69

15.2.18

MEMORY LIMIT ADDRESS REGISTER OFFSET 20h ...................................................70

15.2.19

PREFETCHABLE MEMORY BASE ADDRESS REGISTER OFFSET 24h....................70

15.2.20

PREFETCHABLE MEMORY LIMIT ADDRESS REGISTER OFFSET 24h ..................70

15.2.21

PREFETCHABLE MEMORY BASE ADDRESS UPPER 32-BITS REGISTER OFFSET

28h ...................................................................................................................................................70

15.2.22

PREFETCHABLE MEMORY LIMIT ADDRESS UPPER 32-BITS REGISTER OFFSET

2Ch ...................................................................................................................................................71

15.2.23

I/O BASE ADDRESS UPPER 16-BITS REGISTER OFFSET 30h ...................................71

15.2.24

I/O LIMIT ADDRESS UPPER 16-BITS REGISTER OFFSET 30h ..................................71

15.2.25

CAPABILITY POINTER REGISTER OFFSET 34h ..........................................................71

15.2.26

INTERRUPT LINE REGISTER OFFSET 3Ch ..................................................................71

15.2.27

INTERRUPT PIN REGISTER OFFSET 3Ch .....................................................................71

15.2.28

BRIDGE CONTROL REGISTER OFFSET 3Ch ................................................................72

15.2.29

DIAGNOSTIC/CHIP CONTROL REGISTER OFFSET 40h .............................................73

15.2.30

ARBITER CONTROL REGISTER OFFSET 40h ...............................................................74

15.2.31

EXTENDED CHIP CONTROL REGISTER OFFSET 48h ................................................74

15.2.32

SECONDARY BUS ARBITER PREEMPTION CONTROL REGISTER OFFSET 4Ch ..75

15.2.33

P_SERR# EVENT DISABLE REGISTER OFFSET 64h ...................................................76

15.2.34

SECONDARY CLOCK CONTROL REGISTER OFFSET 68h ..........................................77

15.2.35

P_SERR# STATUS REGISTER OFFSET 68h....................................................................77

15.2.36

CLKRUN REGISTER OFFSET 6Ch ...................................................................................78

15.2.37

PORT OPTION REGISTER OFFSET 74h..........................................................................78

15.2.38

CAPABILITY ID REGISTER OFFSET 80h .......................................................................80

15.2.39

NEXT ITEM POINTER REGISTER OFFSET 80h ............................................................80

15.2.40

POWER MANAGEMENT CAPABILITIES REGISTER OFFSET 80h ............................81

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

Page 8 of 90

JUNE 2004 Revision 1.04

15.2.41

POWER MANAGEMENT DATA REGISTER OFFSET 84h.............................................81

15.2.42

PPB SUPPORT EXTENSIONS OFFSET 84h ....................................................................81

15.2.43

DATA REGISTER OFFSET 84h..........................................................................................81

15.2.44

PRIMARY MASTER TIMEOUT COUNTER REGISTER OFFSET 88h..........................82

15.2.45

SECONDARY MASTER TIMEOUT COUNTER REGISTER OFFSET 88h ....................82

15.2.46

CAPABILITY ID REGISTER OFFSET 90h .......................................................................82

15.2.47

NEXT ITEM POINTER REGISTER OFFSET 90h ............................................................82

15.2.48

HOT SWAP CAPABILITY STRUCTURE REGISTER OFFSET 90h ...............................82

15.2.49

HOT SWAP SWITCH REGISTER OFFSET 94h ...............................................................83

15.2.50

VPD CAPABILITY ID REGISTER OFFSET A0h..............................................................83

15.2.51

NEXT ITEM POINTER REGISTER OFFSET A0h ...........................................................83

15.2.52

VPD REGISTER OFFSET A0h ...........................................................................................83

15.2.53

VPD DATA REGISTER OFFSET A4h................................................................................84

15.2.54

MISCELLANEOUS CONTROL REGISTER OFFSET C0h ..............................................84

15.2.55

GPIO CONTROL REGISTER OFFSET C4h ......................................................................84

15.2.56

EEPROM CONTROL REGISTER OFFSET C8h...............................................................85

15.2.57

EEPROM ADDRESS REGISTER OFFSET C8h................................................................85

15.2.58

EEPROM DATA REGISTER OFFSET C8h .......................................................................86

15.2.59

EEPROM TEST REGISTER OFFSET CCh .......................................................................86

15.2.60

SUBSYSTEM VENDOR ID REGISTER OFFSET F0h .....................................................86

15.2.61

SUBSYSTEM ID OFFSET F0h............................................................................................87

ELECTRICAL AND TIMING SPECIFICATIONS ............................................................................87

16.1

MAXIMUM

RATINGS.........................................................................................................................87

16.2

SPECIFICATIONS .........................................................................................................................87

16.3

SPECIFICATIONS .........................................................................................................................88

16.4

66MHZ

TIMING ...................................................................................................................................89

16.5

33MHZ

TIMING ...................................................................................................................................89

16.6

POWER

CONSUMPTION....................................................................................................................89

PACKAGE INFORMATION.................................................................................................................90

17.1

160-PIN

LFBGA

PACKAGE

OUTLINE ..............................................................................................90

17.2

PART

NUMBER

ORDERING

INFORMATION .................................................................................90

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

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JUNE 2004 Revision 1.04

LIST OF TABLES

ABLE

2-1.

PCI

RANSACTIONS

.............................................................................................................................19

ABLE

2-2.

RITE

RANSACTION

ORWARDING

..................................................................................................21

ABLE

2-3.

RITE

RANSACTION

ISCONNECT

DDRESS

OUNDARIES

..............................................................23

ABLE

2-4.

EAD

REFETCH

DDRESS

OUNDARIES

............................................................................................25

ABLE

2-5.

EAD

RANSACTION

REFETCHING

....................................................................................................25

ABLE

2-6.

EVICE

UMBER TO

IDSEL

S_AD

APPING

...............................................................................29

ABLE

2-7.

ELAYED

RITE

ARGET

ERMINATION

ESPONSE

..........................................................................33

ABLE

2-8.

ESPONSE TO

OSTED

RITE

ARGET

ERMINATION

........................................................................33

ABLE

2-9.

ESPONSE TO

ELAYED

EAD

ARGET

ERMINATION

.......................................................................34

ABLE

4-1.

UMMARY OF

RANSACTION

RDERING

.............................................................................................43

ABLE

5-1.

ETTING THE

RIMARY

NTERFACE

ETECTED

ARITY

RROR

....................................................49

ABLE

5-2.

ETTING

ECONDARY

NTERFACE

ETECTED

ARITY

RROR

......................................................49

ABLE

5-3.

ETTING

RIMARY

NTERFACE

ASTER

ATA

ARITY

RROR

ETECTED

..................................50

ABLE

5-4.

ETTING

ECONDARY

NTERFACE

ASTER

ATA

ARITY

RROR

ETECTED

..............................50

ABLE

5-5.

SSERTION OF

P_PERR#....................................................................................................................51

ABLE

5-6.

SSERTION OF

S_PERR#....................................................................................................................51

ABLE

5-7.

SSERTION OF

P_SERR#

FOR

ATA

ARITY

RRORS

........................................................................52

ABLE

11-1.

OWER

ANAGEMENT

RANSITIONS

................................................................................................59

LIST OF FIGURES

IGURE

16-1

PCI

IGNAL

IMING

EASUREMENT

ONDITIONS

.........................................................................88

IGURE

17-1

160-

LFBGA

PACKAGE OUTLINE

.................................................................................................90

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

Page 11 of 90

JUNE 2004 Revision 1.04

INTRODUCTION

Product Description

The PI7C8148A is Pericom Semiconductor's PCI-to-PCI Bridge, designed to be fully compliant with
the 32-bit, 66MHz implementation of the PCI Local Bus Specification, Revision 2.2. The PI7C8148A
supports synchronous bus transactions between devices on the Primary Bus and the Secondary Buses
operating up to 66MHz. Both primary and secondary buses must operate at the same frequency. The
primary and secondary buses can also operate in concurrent mode, resulting in added increase in system
performance.

Product Features

32-bit Primary and Secondary Ports run up to 66MHz

Compliant with the PCI Local Bus Specification, Revision 2.2

Compliant with PCI-to-PCI Bridge Architecture Specification, Revision 1.1.

- All I/O and memory commands
- Type 1 to Type 0 configuration conversion
- Type 1 to Type 1 configuration forwarding
- Type 1 configuration write to special cycle conversion

Compliant with the Advanced Configuration Power Interface (ACPI)

Compliant with the PCI Power Management Specification, Revision 1.1

Compliant with the PCI Mobile Design Guide, Revision 1.1

Provides internal arbitration for four secondary bus masters

- Programmable 2-level priority arbiter

Supports serial EEPROM interface for register auto-load and VPD access

Supports posted write buffers in all directions

Dynamic Prefetching Control

Four 128 byte FIFO's for delay transactions

Two 128 byte FIFO's for posted memory transactions

Enhanced address decoding

32-bit I/O address range

32-bit memory-mapped I/O address range

64-bit prefetchable address range

Extended commercial temperature range 0°C to 85°C

3.3V and 5V signaling

160-pin LFBGA package

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

Page 13 of 90

JUNE 2004 Revision 1.04

SIGNAL DEFINITIONS

1.1 SIGNAL TYPES

SIGNAL TYPE

DESCRIPTION

I Input

only

O Output

only

P Power
TS Tri-state

bi-directional

STS

Sustained tri-state. Active LOW signal must be pulled HIGH for 1 cycle
when deasserting.

OD Open

Drain

1.2 SIGNALS

Signals that end with "#" are active LOW.

1.2.1 PRIMARY BUS INTERFACE SIGNALS

Name Pin

Number

Type

Description

P_AD[31:0]

P10, N10, M10, P11,
N11, M11, P12, N12,
M14, L12, L13, L14,
K12, K13, K14, J12,
E14, E13, E12, D14,
D13, D12, C13, B14,
B12, A12, C11, B11,
A11, C10, A10, C9

Primary Address / Data: Multiplexed address and data bus.
Address is indicated by P_FRAME# assertion. Write data is
stable and valid when P_IRDY# is asserted and read data is
stable and valid when P_TRDY# is asserted. Data is transferred
on rising clock edges when both P_IRDY# and P_TRDY# are
asserted. During bus idle, PI7C8148A drives P_AD to a valid
logic level when P_GNT# is asserted.

P_CBE#[3:0]

P14, J13, F12, A13

Primary Command/Byte Enables: Multiplexed command field
and byte enable field. During address phase, the initiator drives
the transaction type on these pins. After that, the initiator drives
the byte enables during data phases. During bus idle, PI7C8148A
drives P_CBE#[3:0] to a valid logic level when P_GNT# is
asserted.

P_PAR F13

Primary Parity. Parity is even across P_AD[31:0],
P_CBE#[3:0], and P_PAR (i.e. an even number of 1's). P_PAR
is an input and is valid and stable one cycle after the address
phase (indicated by assertion of P_FRAME#) for address parity.
For write data phases, P_PAR is an input and is valid one clock
after P_IRDY# is asserted. For read data phase, P_PAR is an
output and is valid one clock after P_TRDY# is asserted. Signal
P_PAR is tri-stated one cycle after the P_AD lines are tri-stated.
During bus idle, PI7C8148A drives P_PAR to a valid logic level
when P_GNT# is asserted.

P_FRAME# J14

STS

Primary FRAME (Active LOW). Driven by the initiator of a
transaction to indicate the beginning and duration of an access.
The de-assertion of P_FRAME# indicates the final data phase
requested by the initiator. Before being tri-stated, it is driven to
a de-asserted state for one cycle.

P_IRDY# H12

STS

Primary IRDY (Active LOW). Driven by the initiator of a
transaction to indicate its ability to complete current data phase
on the primary side. Once asserted in a data phase, it is not de-
asserted until the end of the data phase. Before tri-stated, it is
driven to a de-asserted state for one cycle.

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

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Name Pin

Number

Type

Description

P_TRDY# H13

STS

Primary TRDY (Active LOW). Driven by the target of a
transaction to indicate its ability to complete current data phase
on the primary side. Once asserted in a data phase, it is not de-
asserted until the end of the data phase. Before tri-stated, it is
driven to a de-asserted state for one cycle.

P_DEVSEL# H14

STS

Primary Device Select (Active LOW). Asserted by the target
indicating that the device is accepting the transaction. As a
master, PI7C8148A waits for the assertion of this signal within 5
cycles of P_FRAME# assertion; otherwise, terminate with
master abort. Before tri-stated, it is driven to a de-asserted state
for one cycle.

P_STOP# G14

STS

Primary STOP (Active LOW). Asserted by the target
indicating that the target is requesting the initiator to stop the
current transaction. Before tri-stated, it is driven to a de-asserted
state for one cycle.

P_IDSEL N14

Primary ID Select. Used as a chip select line for Type 0
configuration access to PI7C8148A configuration space.

P_PERR# G12

STS

Primary Parity Error (Active LOW). Asserted when a data
parity error is detected for data received on the primary interface.
Before being tri-stated, it is driven to a de-asserted state for one
cycle.

P_SERR# F14

Primary System Error (Active LOW). Can be driven LOW by
any device to indicate a system error condition. PI7C8148A
drives this pin on:
!

Address parity error

Posted write data parity error on target bus

Secondary S_SERR# asserted

Master abort during posted write transaction

Target abort during posted write transaction

Posted write transaction discarded

Delayed write request discarded

Delayed read request discarded

Delayed transaction master timeout

This signal requires an external pull-up resistor for proper
operation.

P_REQ# M9

Primary Request (Active LOW): This is asserted by
PI7C8148A to indicate that it wants to start a transaction on the
primary bus. PI7C8148A de-asserts this pin for at least 2 PCI
clock cycles before asserting it again.

P_GNT# N9

Primary Grant (Active LOW): When asserted, PI7C8148A can
access the primary bus. During idle and P_GNT# asserted,
PI7C8148A will drive P_AD, P_CBE, and P_PAR to valid logic
levels.

P_RST# P8

Primary RESET (Active LOW): When P_RST# is active, all
PCI signals should be asynchronously tri-stated.

1.2.2 SECONDARY BUS INTERFACE SIGNALS

Name Pin

Number

Type

Description

S_AD[31:0]

M1, L3, L2, L1, K3,
K1, J3, J2, H3, H2,
H1, G1, G2, G3, F1,
F2, A3, C4, A4, C5,
B5, A5, C6, B6, C7,
B7, A7, A8, B8, C8,
A9, B9

Secondary Address/Data: Multiplexed address and data bus.
Address is indicated by S_FRAME# assertion. Write data is
stable and valid when S_IRDY# is asserted and read data is
stable and valid when S_TRDY# is asserted. Data is transferred
on rising clock edges when both S_IRDY# and S_TRDY# are
asserted. During bus idle, PI7C8148A drives S_AD to a valid
logic level when S_GNT# is asserted respectively.

S_CBE#[3:0]

J1, F3, A2, A6

Secondary Command/Byte Enables: Multiplexed command
field and byte enable field. During address phase, the initiator
drives the transaction type on these pins. The initiator then
drives the byte enables during data phases. During bus idle,
PI7C8148A drives S_CBE#[3:0] to a valid logic level when the
internal grant is asserted.

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

Page 15 of 90

JUNE 2004 Revision 1.04

Name Pin

Number

Type

Description

S_PAR B1

Secondary Parity: Parity is even across S_AD[31:0],
S_CBE#[3:0], and S_PAR (i.e. an even number of 1's). S_PAR
is an input and is valid and stable one cycle after the address
phase (indicated by assertion of S_FRAME#) for address parity.
For write data phases, S_PAR is an input and is valid one clock
after S_IRDY# is asserted. For read data phase, S_PAR is an
output and is valid one clock after S_TRDY# is asserted. Signal
S_PAR is tri-stated one cycle after the S_AD lines are tri-stated.
During bus idle, PI7C8148A drives S_PAR to a valid logic level
when the internal grant is asserted.

S_FRAME# E2

STS

Secondary FRAME (Active LOW): Driven by the initiator of a
transaction to indicate the beginning and duration of an access.
The de-assertion of S_FRAME# indicates the final data phase
requested by the initiator. Before being tri-stated, it is driven to
a de-asserted state for one cycle.

S_IRDY# E3

STS

Secondary IRDY (Active LOW): Driven by the initiator of a
transaction to indicate its ability to complete current data phase
on the secondary side. Once asserted in a data phase, it is not de-
asserted until the end of the data phase. Before tri-stated, it is
driven to a de-asserted state for one cycle.

S_TRDY# D1

STS

Secondary TRDY (Active LOW): Driven by the target of a
transaction to indicate its ability to complete current data phase
on the secondary side. Once asserted in a data phase, it is not de-
asserted until the end of the data phase. Before tri-stated, it is
driven to a de-asserted state for one cycle.

S_DEVSEL# D2

STS

Secondary Device Select (Active LOW): Asserted by the target
indicating that the device is accepting the transaction. As a
master, PI7C8148A waits for the assertion of this signal within 5
cycles of S_FRAME# assertion; otherwise, terminate with
master abort. Before tri-stated, it is driven to a de-asserted state
for one cycle.

S_STOP# D3

STS

Secondary STOP (Active LOW): Asserted by the target
indicating that the target is requesting the initiator to stop the
current transaction. Before tri-stated, it is driven to a de-asserted
state for one cycle.

S_PERR# C1

STS

Secondary Parity Error (Active LOW): Asserted when a data
parity error is detected for data received on the secondary
interface. Before being tri-stated, it is driven to a de-asserted
state for one cycle.

S_SERR# C2

Secondary System Error (Active LOW): Can be driven LOW
by any device to indicate a system error condition.

S_REQ#[3:0] P2,

P1, N1, M2

Secondary Request (Active LOW): This is asserted by an
external device to indicate that it wants to start a transaction on
the secondary bus. The input is externally pulled up through a
resistor to VDD.

S_GNT#[3:0]

N4, M4, P3, N3

Secondary Grant (Active LOW): PI7C8148A asserts these
pins to allow external masters to access the secondary bus.
PI7C8148A de-asserts these pins for at least 2 PCI clock cycles
before asserting it again. During idle and S_GNT# deasserted,
PI7C8148A will drive S_AD, S_CBE, and S_PAR.

S_RST# P4

Secondary RESET (Active LOW): Asserted when any of the
following conditions are met:
1.

Signal P_RST# is asserted.

Secondary reset bit in bridge control register in
configuration space is set.

When asserted, all control signals are tri-stated and zeroes are
driven on S_AD, S_CBE, and S_PAR.

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1.2.3 CLOCK SIGNALS

Name Pin

Number

Type

Description

P_CLK M8

Primary Clock Input: Provides timing for all transactions on
the primary interface.

S_CLKIN M5

Secondary Clock Input: Provides timing for all transactions on
the secondary interface.

S_CLKOUT[4:0] M7,

P6, N6, M6, P5

Secondary Clock Output: Provides secondary clocks phase
synchronous with the P_CLK.

One of the clock outputs must be fed back to S_CLKIN. Unused
outputs may be disabled by:
1. Writing the secondary clock disable bits in the configuration
space
2. Terminating them electrically.

P_CLKRUN# A14

Primary Clock Run: Allows main system to stop the primary
clock based on the specifications in the PCI Mobile Design
Guide, Revision 1.0. If unused, this pin should be tied to ground
to signify that P_CLK is always running.

S_CLKRUN# B3

Secondary Clock Run: Allows main system to slow down or
stop the secondary clock and is controlled by the primary or
bit[4] offset 6Fh. If the secondary devices do not support
CLKRUN, this pin should be pulled LOW by a 300 ohm resistor.

1.2.4 MISCELLANEOUS SIGNALS

Name Pin

Number

Type

Description

ENUM# B4

Hot Swap Status Indicator: The output of ENUM# indicates to
the system that an insertion has occurred or that an extraction is
about to occur.

LOO B10

I/O

Hot Swap LED: The output of this pin lights an LED to indicate
insertion or removal ready status. This pin may also be used as a
input or detect pin. Every 500us, the pin tri-states for 8 primary
PCI clock cycles to sample the status.

EJECT C14

Hot Swap Switch. When driven LOW, this signal indicates that
the board ejector handle indicates an insertion or impending
extraction of a board.

EECLK G13

EEPROM Clock: Clock signal to the EEPROM interface

EEPD E1

EEPROM Data: Serial data interface to the EEPROM

P_VIO P9

Primary I/O Voltage: This pin is used to determine either 3.3V
or 5V signaling on the primary bus. P_VIO must be tied to 3.3V
only when all devices on the primary bus use 3.3V signaling.
Otherwise, P_VIO is tied to 5V.

S_VIO N5

Secondary I/O Voltage: This pin is used to determine either
3.3V or 5V signaling on the secondary bus. S_VIO must be tied
to 3.3V only when all devices on the secondary bus use 3.3V
signaling. Otherwise, S_VIO is tied to 5V.

SCAN_TM# P7

Full-Scan Test Mode Enable: For normal operation, pull
SCAN_TM# to HIGH. Manufacturing test pin.

SCAN_EN N7

I/O

Full-Scan Enable Control: For normal operation, SCAN_TM#
should be pulled HIGH and SCAN_EN becomes an output with
logic 0. Manufacturing test pin.

BPCEE A1

Bus/Power Clock Control Management Pin: When this pin is
tied HIGH and the PI7C8148A is placed in the D3

HOT

power

state, it enables the PI7C8148A to place the secondary bus in the
B2 power state. The secondary clocks are disabled and driven to
0. When this pin is tied LOW, there is no effect on the secondary
bus clocks when the PI7C8148A enters the D3

HOT

power state.

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1.3 PIN LIST 160-PIN LFBGA

Pin Number

Name

Type

Pin Number

Name

Type

A1 BPCEE I

S_CBE#[1]

A3 S_AD[15] TS

A4 S_AD[13] TS

A5 S_AD[10] TS

A6 S_CBE#[0] TS

A7 S_AD[5] TS

A8 S_AD[4] TS

A9 S_AD[1] TS A10 P_AD[1] TS

A11 P_AD[3] TS

A12 P_AD[6] TS

A13 P_CBE#[0] TS

A14 P_CLKRUN# TS

B1 S_PAR TS B2 VSS P
B3 S_CLKRUN# TS

ENUM#

B5 S_AD[11] TS

B6 S_AD[8] TS

B7 S_AD[6] TS

B8 S_AD[3] TS

B9 S_AD[0] TS B10 LOO I/O

B11 P_AD[4] TS

B12 P_AD[7] TS

B13 VSS P B14

P_AD[8]

C1 S_PERR# STS

C2 S_SERR# I

C3 VSS P C4

S_AD[14]

C5 S_AD[12] TS

C6 S_AD[9] TS

C7 S_AD[7] TS

C8 S_AD[2] TS

C9 P_AD[0] TS C10 P_AD[2] TS

C11 P_AD[5] TS

C12 VSS

C13 P_AD[9] TS

C14 EJECT I

D1 S_TRDY# STS

S_DEVSEL#

STS

D3 S_STOP# STS

D4 VSS

D5 VSS P D6 VDD P
D7 VDD P D8 VDD P
D9 VDD P D10 VSS P

D11 VSS P D12

P_AD[10]

D13 P_AD[11] TS

D14 P_AD[12] TS

E1 EEPD TS E2

S_FRAME#

STS

E3 S_IRDY# STS

E4 VSS

E11 VSS P E12

P_AD[13]

E13 P_AD[14] TS

E14 P_AD[15] TS

F1 S_AD[17] TS

F2 S_AD[16] TS

F3 S_CBE#[2] TS

VDD

F11 VDD P F12

P_CBE#[1]

F13 P_PAR TS F14 P_SERR# OD

G1 S_AD[20] TS

G2 S_AD[19] TS

G3 S_AD[18] TS

G4 VDD

G11 VDD P G12

P_PERR#

G12

G13 EECLK O

G14 P_STOP# I

H1 S_AD[21] TS

H2 S_AD[22] TS

H3 S_AD[23] TS

H4 VDD

H11 VDD

H12 P_IRDY# STS

H13 P_TRDY# STS

H14

P_DEVSEL# STS

J1 S_CBE#[3] TS

J2 S_AD[24] TS

J3 S_AD[25] TS

J4 VDD

J11 VDD P J12

P_AD[16]

J13 P_CBE#[2] TS

J14 P_FRAME# STS

K1 S_AD[26] TS

K2 GPIO[0] TS

S_AD[27]

TS K4 VSS P

K11 VSS P K12

P_AD[19]

K13 P_AD[18] TS

K14 P_AD[17] TS

L1 S_AD[28] TS

L2 S_AD[29] TS

L3 S_AD[30] TS

VSS

L5 VSS

P L6

VDD P

L7 VDD P L8 VDD P
L9 VDD P L10 VSS P

L11 VSS P L12

P_AD[22]

L13 P_AD[21] TS

L14 P_AD[20] TS

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Pin Number

Name

Type

Pin Number

Name

Type

M1 S_AD[31] TS

M2 S_REQ#[0] I

M3 VSS P M4

S_GNT#[2]

M5 S_CLKIN I

S_CLKOUT[1]

M7 S_CLKOUT[4] O

P_CLK

M9 P_REQ# TS M10

P_AD[29] TS

M11 P_AD[26] TS

M12

VSS

M13 GPIO[3] TS

M14 P_AD[23] TS

N1 S_REQ#[1] I

VSS

N3 S_GNT#[0] TS

N4 S_GNT#[3] TS

N5 S_VIO I

S_CLKOUT[2]

N7 SCAN_EN I/O

N8 GPIO[1] TS

N9 P_GNT# I

N10 P_AD[30] TS

N11 P_AD[27] TS

N12 P_AD[24] TS

N13 VSS P N14

P_IDSEL I

P1 S_REQ#[2] I

P2 S_REQ#[3] I

P3 S_GNT#[1] TS

P4 S_RST# O

P5 S_CLKOUT[0] O

P6 S_CLKOUT[3] O

P7 SCAN_TM# I

P8 P_RST#

P9 P_VIO I P10

P_AD[31]

P11 P_AD[28] TS

P12 P_AD[25] TS

P13 GPIO[2] TS

P14

P_CBE#[3] TS

PCI BUS OPERATION

This Chapter offers information about PCI transactions, transaction forwarding across the bridge, and
transaction termination. The bridge has two 128-byte FIFO's for buffering of upstream and
downstream transactions. These hold addresses, data, commands, and byte enables that are used for
write transactions. The bridge also has an additional four 128-byte FIFO's that hold addresses, data,
commands, and byte enables for read transactions.

2.1 TYPES OF TRANSACTIONS

This section provides a summary of PCI transactions performed by the bridge. Table 2-1 lists the
command code and name of each PCI transaction. The Master and Target columns indicate support for
each transaction when the bridge initiates transactions as a master, on the primary (P) and secondary (S)
buses, and when the bridge responds to transactions as a target, on the primary (P) and secondary (S)
buses.

Table 2-1. PCI Transactions

Types of Transactions

Initiates as Master

Responds as Target

Primary

Secondary

Primary

Secondary

0000 Interrupt

Acknowledge

0001 Special

Cycle

0010 I/O

Read

0011 I/O

Write

0100 Reserved

0101 Reserved

0110 Memory

Read

0111 Memory

Write

1000 Reserved

1001 Reserved

1010 Configuration

Read

1011

Configuration Write

Y (Type 1 only)

1100

Memory Read Multiple

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Types of Transactions

Initiates as Master

Responds as Target

Primary

Secondary

Primary

Secondary

1101

Dual Address Cycle

1110

Memory Read Line

1111

Memory Write and Invalidate

As indicated in Table 2-1, the following PCI commands are not supported by the bridge:

!

The bridge never initiates a PCI transaction with a reserved command code and, as a target, the

bridge ignores reserved command codes.

The bridge does not generate interrupt acknowledge transactions. The bridge ignores interrupt

acknowledge transactions as a target.

The bridge does not respond to special cycle transactions. The bridge cannot guarantee delivery of

a special cycle transaction to downstream buses because of the broadcast nature of the special cycle
command and the inability to control the transaction as a target. To generate special cycle
transactions on other PCI buses, either upstream or downstream, Type 1 configuration write must
be used.

The bridge neither generates Type 0 configuration transactions on the primary PCI bus nor

responds to Type 0 configuration transactions on the secondary PCI buses.

2.2 SINGLE ADDRESS PHASE

A 32-bit address uses a single address phase. This address is driven on P_AD[31:0], and the bus
command is driven on P_CBE[3:0]. The bridge supports the linear increment address mode only, which
is indicated when the lowest two address bits are equal to zero. If either of the lowest two address bits is
nonzero, the bridge automatically disconnects the transaction after the first data transfer.

2.3 DEVICE SELECT (DEVSEL#) GENERATION

The bridge always performs positive address decoding (medium decode) when accepting transactions
on either the primary or secondary buses. The bridge never does subtractive decode.

2.4 DATA PHASE

The address phase of a PCI transaction is followed by one or more data phases. A data phase is
completed when IRDY# and either TRDY# or STOP# are asserted. A transfer of data occurs only
when both IRDY# and TRDY# are asserted during the same PCI clock cycle. The last data phase of a
transaction is indicated when FRAME# is de-asserted and both TRDY# and IRDY# are asserted, or
when IRDY# and STOP# are asserted. See Section 2.8 for further discussion of transaction termination.

Depending on the command type, the bridge can support multiple data phase PCI transactions. For
detailed descriptions of how the bridge imposes disconnect boundaries, see Section 2.5.4 for write
address boundaries and Section 2.6.4 read address boundaries.

2.5 WRITE TRANSACTIONS

Write transactions are treated as either posted write or delayed write transactions. Table 2-2 shows the
method of forwarding used for each type of write operation.

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Table 2-2. Write Transaction Forwarding

Type of Transaction

Type of Forwarding

Memory Write

Posted (except VGA memory)

Memory Write and Invalidate

Posted

Memory Write to VGA memory

Delayed

I/O Write

Delayed

Type 1 Configuration Write

Delayed

2.5.1 MEMORY WRITE TRANSACTIONS

Posted write forwarding is used for "Memory Write" and "Memory Write and Invalidate" transactions.

When the bridge determines that a memory write transaction is to be forwarded across the bridge, the
bridge asserts DEVSEL# with medium timing and TRDY# in the next cycle, provided that enough
buffer space is available in the posted memory write queue for the address and at least one DWORD of
data. Under this condition, the bridge accepts write data without obtaining access to the target bus. The
bridge can accept one DWORD of write data every PCI clock cycle. That is, no target wait state is
inserted. The write data is stored in an internal posted write buffers and is subsequently delivered to the
target. The bridge continues to accept write data until one of the following events occurs:

!

The initiator terminates the transaction by de-asserting FRAME# and IRDY#.

An internal write address boundary is reached, such as a cache line boundary or an aligned 4KB

boundary, depending on the transaction type.

The posted write data buffer fills up.

When one of the last two events occurs, the bridge returns a target disconnect to the requesting initiator
on this data phase to terminate the transaction.

Once the posted write data moves to the head of the posted data queue, the bridge asserts its request on
the target bus. This can occur while the bridge is still receiving data on the initiator bus. When the
grant for the target bus is received and the target bus is detected in the idle condition, the bridge asserts
FRAME# and drives the stored write address out on the target bus. On the following cycle, the bridge
drives the first DWORD of write data and continues to transfer write data until all write data
corresponding to that transaction is delivered, or until a target termination is received. As long as write
data exists in the queue, the bridge can drive one DWORD of write data each PCI clock cycle; that is,
no master wait states are inserted. If write data is flowing through the bridge and the initiator stalls, the
bridge will signal the last data phase for the current transaction at the target bus if the queue empties.
The bridge will restart the follow-on transactions if the queue has new data.

The bridge ends the transaction on the target bus when one of the following conditions is met:

!

All posted write data has been delivered to the target.

The target returns a target disconnect or target retry (the bridge starts another transaction to deliver

the rest of the write data).

The target returns a target abort (the bridge discards remaining write data).

The master latency timer expires, and the bridge no longer has the target bus grant (the bridge starts

another transaction to deliver remaining write data).

Section 2.8.3.2 provides detailed information about how the bridge responds to target termination
during posted write transactions.

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2.5.2 MEMORY WRITE AND INVALIDATE

Posted write forwarding is used for Memory Write and Invalidate transactions.

If offset 74h bits [8:7] = 11, the bridge disconnects Memory Write and Invalidate commands at aligned
cache line boundaries. The cache line size value in the cache line size register gives the number of
DWORD in a cache line.

If offset 74h bits [8:7] = 00, the bridge converts Memory Write and Invalidate transactions to Memory
Write transactions at the destination.

If the value in the cache line size register does meet the memory write and invalidate conditions, the
bridge returns a target disconnect to the initiator on a cache line boundary.

2.5.3 DELAYED WRITE TRANSACTIONS

Delayed write forwarding is used for I/O write transactions and Type 1 configuration write transactions.

A delayed write transaction guarantees that the actual target response is returned back to the initiator
without holding the initiating bus in wait states. A delayed write transaction is limited to a single
DWORD data transfer.

When a write transaction is first detected on the initiator bus, and the bridge forwards it as a delayed
transaction, the bridge claims the access by asserting DEVSEL# and returns a target retry to the
initiator. During the address phase, the bridge samples the bus command, address, and address parity
one cycle later. After IRDY# is asserted, the bridge also samples the first data DWORD, byte enable
bits, and data parity. This information is placed into the delayed transaction queue. The transaction is
queued only if no other existing delayed transactions have the same address and command, and if the
delayed transaction queue is not full. When the delayed write transaction moves to the head of the
delayed transaction queue and all ordering constraints with posted data are satisfied. The bridge initiates
the transaction on the target bus. The bridge transfers the write data to the target. If the bridge receives
a target retry in response to the write transaction on the target bus, it continues to repeat the write
transaction until the data transfer is completed, or until an error condition is encountered.

If the bridge is unable to deliver write data after 2

(default) or 2

(maximum) attempts, the bridge will

report a system error. The bridge also asserts P_SERR# if the primary SERR# enable bit is set in the
command register. See Section 5.4 for information on the assertion of P_SERR#. When the initiator
repeats the same write transaction (same command, address, byte enable bits, and data), and the
completed delayed transaction is at the head of the queue, the bridge claims the access by asserting
DEVSEL# and returns TRDY# to the initiator, to indicate that the write data was transferred. If the
initiator requests multiple DWORD, the bridge also asserts STOP# in conjunction with TRDY# to
signal a target disconnect. Note that only those bytes of write data with valid byte enable bits are
compared. If any of the byte enable bits are turned off (driven HIGH), the corresponding byte of write
data is not compared.

If the initiator repeats the write transaction before the data has been transferred to the target, the bridge
returns a target retry to the initiator. The bridge continues to return a target retry to the initiator until
write data is delivered to the target, or until an error condition is encountered. When the write
transaction is repeated, the bridge does not make a new entry into the delayed transaction queue.
Section 2.8.3.1 provides detailed information about how the bridge responds to target termination
during delayed write transactions.

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The bridge implements a discard timer that starts counting when the delayed write completion is at the
head of the delayed transaction completion queue. The initial value of this timer can be set to the retry
counter register offset 88h.

If the initiator does not repeat the delayed write transaction before the discard timer expires, the bridge
discards the delayed write completion from the delayed transaction completion queue. The bridge also
conditionally asserts P_SERR# (see Section 5.4).

2.5.4 WRITE TRANSACTION BOUNDARIES

The bridge imposes internal address boundaries when accepting write data. The aligned address
boundaries are used to prevent the bridge from continuing a transaction over a device address boundary
and to provide an upper limit on maximum latency. The bridge returns a target disconnect to the
initiator when it reaches the aligned address boundaries under conditions shown in Table 2-3.

Table 2-3. Write Transaction Disconnect Address Boundaries

Type of Transaction

Condition Aligned

Address

Boundary

Delayed Write

All

Disconnects after one data transfer

Posted Memory Write

Memory write disconnect control bit = 0

(1)

4KB aligned address boundary

Posted Memory Write

Memory write disconnect control bit = 1

(1)

Disconnects at cache line boundary

Posted Memory Write and
Invalidate

Cache line size

1, 2, 4, 8, 16

4KB aligned address boundary

Posted Memory Write and
Invalidate

Cache line size = 1, 2, 4, 8, 16

Cache line boundary if posted memory
write data FIFO does not have enough
space for the cache line

Note 1. Memory write disconnect control bit is bit 1 of the chip control register at offset 44h in the configuration space.

2.5.5 BUFFERING MULTIPLE WRITE TRANSACTIONS

The bridge continues to accept posted memory write transactions as long as space for at least one
DWORD of data in the posted write data buffer remains. If the posted write data buffer fills before the
initiator terminates the write transaction, the bridge returns a target disconnect to the initiator.

Delayed write transactions are posted as long as at least one open entry in the delayed transaction queue
exists. Therefore, several posted and delayed write transactions can exist in data buffers at the same
time. See Chapter 5 for information about how multiple posted and delayed write transactions are
ordered.

2.5.6 FAST BACK-TO-BACK TRANSACTIONS

The bridge can recognize and post fast back-to-back write transactions. When the bridge cannot accept
the second transaction because of buffer space limitations, it returns a target retry to the initiator. The
fast back-to-back enable bit must be set in the command register for upstream write transactions, and in
the bridge control register for downstream write transactions.

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2.6 READ TRANSACTIONS

Delayed read forwarding is used for all read transactions crossing the bridge. Delayed read transactions
are treated as either prefetchable or non-prefetchable. Table 2-5 shows the read behavior, prefetchable
or non-prefetchable, for each type of read operation.

2.6.1 PREFETCHABLE READ TRANSACTIONS

A prefetchable read transaction is a read transaction where the bridge performs speculative DWORD
reads, transferring data from the target before it is requested from the initiator. This behavior allows a
prefetchable read transaction to consist of multiple data transfers. However, byte enable bits cannot be
forwarded for all data phases as is done for the single data phase of the non-prefetchable read
transaction. For prefetchable read transactions, the bridge forces all byte enable bits to be turned on for
all data phases.

Prefetchable behavior is used for memory read line and memory read multiple transactions, as well as
for memory read transactions that fall into prefetchable memory space.

The amount of data that is pre-fetched depends on the type of transaction. The amount of pre-fetching
may also be affected by the amount of free buffer space available in the bridge, and by any read address
boundaries encountered.

Pre-fetching should not be used for those read transactions that have side effects in the target device,
that is, control and status registers, FIFO's, and so on. The target device's base address register or
registers indicate if a memory address region is prefetchable.

2.6.2 DYNAMIC PREFETCHING CONTROL

For prefetchable reads described in the previous section, the prefetching length is normally predefined
and cannot be changed once it is set. This may cause some inefficiency as the prefetching length
determined could be larger or smaller than the actual data being prefetched. To make prefetching more
efficient, PI7C8148A incorporates dynamic prefetching control logic. This logic regulates the different
PCI memory read commands (MR memory read, MRL memory read line, and MRM memory
read multiple) to improve memory read burst performance. The bridge tracks every memory read burst
transaction and tallies the status. By using the status information, the bridge can determine to increase,
reduce, or keep the same cache line length to be prefetched. Over time, the bridge can better match the
correct cache line setting to the length of data being requested. The dynamic prefetching control logic is
set with bits[3:2] offset 48h.

2.6.3 NON-PREFETCHABLE READ TRANSACTIONS

A non-prefetchable read transaction is a read transaction where the bridge requests one and only one
DWORD from the target and disconnects the initiator after delivery of the first DWORD of read data.
Unlike prefetchable read transactions, the bridge forwards the read byte enable information for the data
phase.

Non-prefetchable behavior is used for I/O and configuration read transactions, as well as for memory
read transactions that fall into non-prefetchable memory space.

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If extra read transactions could have side effects, for example, when accessing a FIFO, use non-
prefetchable read transactions to those locations. Accordingly, if it is important to retain the value of the
byte enable bits during the data phase, use non-prefetchable read transactions. If these locations are
mapped in memory space, use the memory read command and map the target into non-prefetchable
(memory-mapped I/O) memory space to use non-prefetching behavior.

2.6.4 READ PREFETCH ADDRESS BOUNDARIES

The bridge imposes internal read address boundaries on read pre-fetched data. When a read transaction
reaches one of these aligned address boundaries, the bridge stops pre-fetched data, unless the target
signals a target disconnect before the read pre-fetched boundary is reached. When the bridge finishes
transferring this read data to the initiator, it returns a target disconnect with the last data transfer, unless
the initiator completes the transaction before all pre-fetched read data is delivered. Any leftover pre-
fetched data is discarded.

Prefetchable read transactions in flow-through mode pre-fetch to the nearest aligned 4KB address
boundary, or until the initiator de-asserts FRAME_L. Section 2.6.7 describes flow-through mode during
read operations.

Table 2-4 shows the read prefetch address boundaries for read transactions during non-flow-through
mode.

Table 2-4. Read Prefetch Address Boundaries

Type of Transaction

Address Space

Cache Line Size
(CLS)

Prefetch Aligned Address Boundary

Configuration Read

One DWORD (no prefetch)

I/O Read

One DWORD (no prefetch)

Memory Read

Non-Prefetchable

One DWORD (no prefetch)

Memory Read

Prefetchable

CLS = 0 or 16

16-DWORD aligned address boundary

Memory Read

Prefetchable

CLS = 1, 2, 4, 8, 16

Cache line address boundary

Memory Read Line

CLS = 0 or 16

16-DWORD aligned address boundary

Memory Read Line

CLS = 1, 2, 4, 8, 16

Cache line boundary

Memory Read Multiple

CLS = 0 or 16

32-DWORD aligned address boundary

Memory Read Multiple

CLS = 1, 2, 4, 8, 16

2X of cache line boundary

- does not matter if it is prefetchable or non-prefetchable
* don't care

Table 2-5. Read Transaction Prefetching

Type of Transaction

Read Behavior

I/O Read

Prefetching never allowed

Configuration Read

Prefetching never allowed
Downstream: Prefetching used if address is prefetchable space

Memory Read

Upstream: Prefetching used or programmable

Memory Read Line

Prefetching always used

Memory Read Multiple

Prefetching always used

See Section 3.3 for detailed information about prefetchable and non-prefetchable address spaces.

2.6.5 DELAYED READ REQUESTS

The bridge treats all read transactions as delayed read transactions, which means that the read request
from the initiator is posted into a delayed transaction queue. Read data from the target is placed in the

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read data queue directed toward the initiator bus interface and is transferred to the initiator when the
initiator repeats the read transaction.

When the bridge accepts a delayed read request, it first samples the read address, read bus command,
and address parity. When IRDY# is asserted, the bridge then samples the byte enable bits for the first
data phase. This information is entered into the delayed transaction queue. The bridge terminates the
transaction by signaling a target retry to the initiator. Upon reception of the target retry, the initiator is
required to continue to repeat the same read transaction until at least one data transfer is completed, or
until a target response (target abort or master abort) other than a target retry is received.

2.6.6 DELAYED READ COMPLETION WITH TARGET

When delayed read request reaches the head of the delayed transaction queue, the bridge arbitrates for
the target bus and initiates the read transaction only if all previously queued posted write transactions
have been delivered. The bridge uses the exact read address and read command captured from the
initiator during the initial delayed read request to initiate the read transaction. If the read transaction is a
non-prefetchable read, the bridge drives the captured byte enable bits during the next cycle. If the
transaction is a prefetchable read transaction, it drives all byte enable bits to zero for all data phases. If
the bridge receives a target retry in response to the read transaction on the target bus, it continues to
repeat the read transaction until at least one data transfer is completed, or until an error condition is
encountered. If the transaction is terminated via normal master termination or target disconnect after at
least one data transfer has been completed, the bridge does not initiate any further attempts to read more
data.

If the bridge is unable to obtain read data from the target after 2

(default) or 2

(maximum) attempts,

the bridge will report system error. The number of attempts is programmable. The bridge also asserts
P_SERR# if the primary SERR# enable bit is set in the command register. See Section 5.4 for
information on the assertion of P_SERR#.

Once the bridge receives DEVSEL# and TRDY# from the target, it transfers the data read to the
opposite direction read data queue, pointing toward the opposite inter-face, before terminating the
transaction. For example, read data in response to a downstream read transaction initiated on the
primary bus is placed in the upstream read data queue. The bridge can accept one DWORD of read data
each PCI clock cycle; that is, no master wait states are inserted. The number of DWORD's transferred
during a delayed read transaction depends on the conditions given in Table 2-4 (assuming no disconnect
is received from the target).

2.6.7 DELAYED READ COMPLETION ON INITIATOR BUS

When the transaction has been completed on the target bus, and the delayed read data is at the head of
the read data queue, and all ordering constraints with posted write transactions have been satisfied, the
bridge transfers the data to the initiator when the initiator repeats the transaction. For memory read
transactions, the bridge aliases the memory read, memory read line, and memory read multiple bus
commands when matching the bus command of the transaction to the bus command in the delayed
transaction queue. The bridge returns a target disconnect along with the transfer of the last DWORD of
read data to the initiator. If the bridge initiator terminates the transaction before all read data has been
transferred, the remaining read data left in data buffers is discarded.

When the master repeats the transaction and starts transferring prefetchable read data from data buffers
while the read transaction on the target bus is still in progress and before a read boundary is reached on
the target bus, the read transaction starts operating in flow-through mode. Because data is flowing

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through the data buffers from the target to the initiator, long read bursts can then be sustained. In this
case, the read transaction is allowed to continue until the initiator terminates the transaction, or until an
aligned 4KB address boundary is reached, or until the buffer fills, whichever comes first. When the
buffer empties, the bridge reflects the stalled condition to the initiator by disconnecting the initiator
with data. The initiator may retry the transaction later if data are needed. If the initiator does not need
any more data, the initiator will not continue the disconnected transaction. In this case, the bridge will
start the master timeout timer. The remaining read data will be discarded after the master timeout timer
expires. To provide better latency, if there are any other pending data for other transactions in the RDB
(Read Data Buffer), the remaining read data will be discarded even though the master timeout timer has
not expired.

The bridge implements a master timeout timer that starts counting when the delayed read completion is
at the head of the delayed transaction queue, and the read data is at the head of the read data queue. The
initial value of this timer is programmable through configuration register. If the initiator does not repeat
the read transaction and before the master timeout timer expires (2

default), the bridge discards the

read transaction and read data from its queues. The bridge also conditionally asserts P_SERR# (see
Section 5.4).

The bridge has the capability to post multiple delayed read requests, up to a maximum of four in each
direction. If an initiator starts a read transaction that matches the address and read command of a read
transaction that is already queued, the current read command is not posted as it is already contained in
the delayed transaction queue.

See Section 4 for a discussion of how delayed read transactions are ordered when crossing the bridge.

2.6.8 FAST BACK-TO-BACK READ TRANSACTIONS

The bridge can recognize fast back-to-back read transactions.

2.7 CONFIGURATION TRANSACTIONS

Configuration transactions are used to initialize a PCI system. Every PCI device has a configuration
space that is accessed by configuration commands. All registers are accessible in configuration space
only.

In addition to accepting configuration transactions for initialization of its own configuration space, the
bridge also forwards configuration transactions for device initialization in hierarchical PCI systems, as
well as for special cycle generation.

To support hierarchical PCI bus systems, two types of configuration transactions are specified: Type 0
and Type 1.

Type 0 configuration transactions are issued when the intended target resides on the same PCI bus as
the initiator. A Type 0 configuration transaction is identified by the configuration command and the
lowest two bits of the address set to 00b.

Type 1 configuration transactions are issued when the intended target resides on another PCI bus, or
when a special cycle is to be generated on another PCI bus. A Type 1 configuration command is
identified by the configuration command and the lowest two address bits set to 01b.

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The register number is found in both Type 0 and Type 1 formats and gives the DWORD address of the
configuration register to be accessed. The function number is also included in both Type 0 and Type 1
formats and indicates which function of a multifunction device is to be accessed. For single-function
devices, this value is not decoded. The addresses of Type 1 configuration transaction include a 5-bit
field designating the device number that identifies the device on the target PCI bus that is to be
accessed. In addition, the bus number in Type 1 transactions specifies the PCI bus to which the
transaction is targeted.

2.7.1 TYPE 0 ACCESS TO PI7C8148A

The configuration space is accessed by a Type 0 configuration transaction on the primary interface. The
configuration space cannot be accessed from the secondary bus. The bridge responds to a Type 0
configuration transaction by asserting P_DEVSEL# when the following conditions are met during the
address phase:

!

The bus command is a configuration read or configuration write transaction.

Lowest two address bits P_AD[1:0] must be 00b.

Signal P_IDSEL must be asserted.

The bridge limits all configuration access to a single DWORD data transfer and returns target-
disconnect with the first data transfer if additional data phases are requested. Because read transactions
to configuration space do not have side effects, all bytes in the requested DWORD are returned,
regardless of the value of the byte enable bits.

Type 0 configuration write and read transactions do not use data buffers; that is, these transactions are
completed immediately, regardless of the state of the data buffers. The bridge ignores all Type 0
transactions initiated on the secondary interface.

2.7.2 TYPE 1 TO TYPE 0 CONVERSION

Type 1 configuration transactions are used specifically for device configuration in a hierarchical PCI
bus system. A PCI-to-PCI bridge is the only type of device that should respond to a Type 1
configuration command. Type 1 configuration commands are used when the configuration access is
intended for a PCI device that resides on a PCI bus other than the one where the Type 1 transaction is
generated.

The bridge performs a Type 1 to Type 0 translation when the Type 1 transaction is generated on the
primary bus and is intended for a device attached directly to the secondary bus. The bridge must convert
the configuration command to a Type 0 format so that the secondary bus device can respond to it. Type
1 to Type 0 translations are performed only in the downstream direction; that is, the bridge generates a
Type 0 transaction only on the secondary bus, and never on the primary bus.

The bridge responds to a Type 1 configuration transaction and translates it into a Type 0 transaction on
the secondary bus when the following conditions are met during the address phase:

!

The lowest two address bits on P_AD[1:0] are 01b.

The bus number in address field P_AD[23:16] is equal to the value in the secondary bus number

The bus command on P_CBE[3:0] is a configuration read or configuration write transaction.

When the bridge translates the Type 1 transaction to a Type 0 transaction on the secondary
interface, it performs the following translations to the address:

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Sets the lowest two address bits on S_AD[1:0].

Decodes the device number and drives the bit pattern specified in Table 2-6 on S_AD[31:16] for

the purpose of asserting the device's IDSEL signal.

Sets S_AD[15:11] to 0.

Leaves unchanged the function number and register number fields.

The bridge asserts a unique address line based on the device number. These address lines may be used
as secondary bus IDSEL signals. The mapping of the address lines depends on the device number in the
Type 1 address bits P_AD[15:11]. presents the mapping that the bridge uses.

Table 2-6. Device Number to IDSEL S_AD Pin Mapping

Device Number

P_AD[15:11]

Secondary IDSEL S_AD[31:16]

S_AD

00000

0000 0000 0000 0001

00001

0000 0000 0000 0010

00010

0000 0000 0000 0100

00011

0000 0000 0000 1000

00100

0000 0000 0001 0000

00101

0000 0000 0010 0000

00110

0000 0000 0100 0000

00111

0000 0000 1000 0000

01000

0000 0001 0000 0000

01001

0000 0010 0000 0000

01010

0000 0100 0000 0000

01011

0000 1000 0000 0000

01100

0001 0000 0000 0000

01101

0010 0000 0000 0000

01110

0100 0000 0000 0000

01111

1000 0000 0000 0000

10h 1Eh

10000 11110

0000 0000 0000 0000

1Fh

11111

Generate special cycle (P_AD[7:2] > 00h)
0000 0000 0000 0000 (P_AD[7:2] = 00h)

The bridge can assert up to 16 unique address lines to be used as IDSEL signals for
up to 16 devices on the secondary bus, for device numbers ranging from 0 through 15. Because of
electrical loading constraints of the PCI bus, more than 9 IDSEL signals should not be necessary.
However, if device numbers greater than 15 are desired, some external method of generating IDSEL
lines must be used, and no upper address bits are then asserted. The configuration transaction is still
translated and passed from the primary bus to the secondary bus. If no IDSEL pin is asserted to a
secondary device, the transaction ends in a master abort.

The bridge forwards Type 1 to Type 0 configuration read or write transactions as delayed transactions.
Type 1 to Type 0 configuration read or write transactions are limited to a single 32-bit data transfer.

2.7.3 TYPE 1 TO TYPE 1 FORWARDING

Type 1 to Type 1 transaction forwarding provides a hierarchical configuration mechanism when two or
more levels of PCI-to-PCI bridges are used.

When the bridge detects a Type 1 configuration transaction intended for a PCI bus downstream from
the secondary bus, the bridge forwards the transaction unchanged to the secondary bus. Ultimately, this
transaction is translated to a Type 0 configuration command or to a special cycle transaction by a
downstream PCI-to-PCI bridge. Downstream Type 1 to Type 1 forwarding occurs when the following
conditions are met during the address phase:

!

The lowest two address bits are equal to 01b.

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The bus number falls in the range defined by the lower limit (exclusive) in the secondary bus

number register and the upper limit (inclusive) in the subordinate bus number register.

The bus command is a configuration read or write transaction.

The bridge also supports Type 1 to Type 1 forwarding of configuration write transactions upstream to
support upstream special cycle generation. A Type 1 configuration command is forwarded upstream
when the following conditions are met:

!

The lowest two address bits are equal to 01b.

The bus number falls outside the range defined by the lower limit (inclusive) in the secondary bus

number register and the upper limit (inclusive) in the subordinate bus number register.

The device number in address bits AD[15:11] is equal to 11111b.

The function number in address bits AD[10:8] is equal to 111b.

The bus command is a configuration write transaction.

The bridge forwards Type 1 to Type 1 configuration write transactions as delayed transactions. Type 1
to Type 1 configuration write transactions are limited to a single data transfer.

2.7.4 SPECIAL CYCLES

The Type 1 configuration mechanism is used to generate special cycle transactions in hierarchical PCI
systems. Special cycle transactions are ignored by acting as a target and are not forwarded across the
bridge. Special cycle transactions can be generated from Type 1 configuration write transactions in
either the upstream or the down-stream direction.

The birdge initiates a special cycle on the target bus when a Type 1 configuration write transaction is
being detected on the initiating bus and the following conditions are met during the address phase:

!

The lowest two address bits on AD[1:0] are equal to 01b.

The device number in address bits AD[15:11] is equal to 11111b.

The function number in address bits AD[10:8] is equal to 111b.

The register number in address bits AD[7:2] is equal to 000000b.

The bus number is equal to the value in the secondary bus number register in configuration space

for downstream forwarding or equal to the value in the primary bus number register in
configuration space for upstream forwarding.

The bus command on CBE# is a configuration write command.

When the bridge initiates the transaction on the target interface, the bus command is changed from
configuration write to special cycle. The address and data are for-warded unchanged. Devices that use
special cycles ignore the address and decode only the bus command. The data phase contains the special
cycle message. The transaction is forwarded as a delayed transaction, but in this case the target
response is not forwarded back (because special cycles result in a master abort). Once the transaction is
completed on the target bus, through detection of the master abort condition, the bridge responds with
TRDY# to the next attempt of the con-figuration transaction from the initiator. If more than one data
transfer is requested, the bridge responds with a target disconnect operation during the first data phase.

2.8 TRANSACTION TERMINATION

This section describes how bridge returns transaction termination conditions back to the initiator.

The initiator can terminate transactions with one of the following types of termination:

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Normal termination

Normal termination occurs when the initiator de-asserts FRAME# at the beginning of the last data
phase, and de-asserts IRDY# at the end of the last data phase in conjunction with either TRDY# or
STOP# assertion from the target.

Master abort

A master abort occurs when no target response is detected. When the initiator does not detect a
DEVSEL# from the target within five clock cycles after asserting FRAME#, the initiator terminates
the transaction with a master abort. If FRAME# is still asserted, the initiator de-asserts FRAME#
on the next cycle, and then de-asserts IRDY# on the following cycle. IRDY# must be asserted in
the same cycle in which FRAME# de-asserts. If FRAME# is already de-asserted, IRDY# can be
de-asserted on the next clock cycle following detection of the master abort condition.

The target can terminate transactions with one of the following types of termination:

Normal termination

TRDY# and DEVSEL# asserted in conjunction with FRAME# de-asserted and IRDY# asserted.

Target retry

STOP# and DEVSEL# asserted with TRDY# de-asserted during the first data phase. No data
transfers occur during the transaction. This transaction must be repeated.

Target disconnect with data transfer

STOP#, DEVSEL# and TRDY# asserted. It signals that this is the last data transfer of the
transaction.

Target disconnect without data transfer

STOP# and DEVSEL# asserted with TRDY# de-asserted after previous data transfers have been
made. Indicates that no more data transfers will be made during this transaction.

Target abort

STOP# asserted with DEVSEL# and TRDY# de-asserted. Indicates that target will never be able to
complete this transaction. DEVSEL# must be asserted for at least one cycle during the transaction
before the target abort is signaled.

2.8.1 MASTER TERMINATION INITIATED BY PI7C8148A

The bridge, as an initiator, uses normal termination if DEVSEL# is returned by target within five clock
cycles of the bridge's assertion of FRAME# on the target bus. As an initiator, the bridge terminates a
transaction when the following conditions are met:

!

During a delayed write transaction, a single DWORD is delivered.

During a non-prefetchable read transaction, a single DWORD is transferred from the target.

During a prefetchable read transaction, a pre-fetch boundary is reached.

For a posted write transaction, all write data for the transaction is transferred from data buffers to

the target.

For burst transfer, with the exception of "Memory Write and Invalidate" transactions, the master

latency timer expires and the bridge's bus grant is de-asserted.

The target terminates the transaction with a retry, disconnect, or target abort.

If the bridge is delivering posted write data when it terminates the transaction because the master
latency timer expires, it initiates another transaction to deliver the remaining write data. The address of
the transaction is updated to reflect the address of the current DWORD to be delivered.

If the bridge is pre-fetching read data when it terminates the transaction because the master latency
timer expires, it does not repeat the transaction to obtain more data.

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2.8.2 MASTER ABORT RECEIVED BY PI7C8148A

If the initiator initiates a transaction on the target bus and does not detect DEVSEL# returned by the
target within five clock cycles of the assertion of FRAME#, the bridge terminates the transaction with a
master abort. This sets the received-master-abort bit in the status register corresponding to the target
bus.

For delayed read and write transactions, the bridge is able to reflect the master abort condition back to
the initiator. When the bridge detects a master abort in response to a delayed transaction, and when the
initiator repeats the transaction, the bridge does not respond to the transaction with DEVSEL#, which
induces the master abort condition back to the initiator. The transaction is then removed from the
delayed transaction queue. When a master abort is received in response to a posted write transaction,
the bridge discards the posted write data and makes no more attempts to deliver the data. The bridge
sets the received-master-abort bit in the status register when the master abort is received on the primary
bus, or it sets the received master abort bit in the secondary status register when the master abort is
received on the secondary interface. When master abort is detected in posted write transaction with both
master-abort-mode bit (bit 5 of bridge control register) and the SERR# enable bit (bit 8 of command
register for secondary bus) are set, the bridge asserts P_SERR# if the master-abort-on-posted-write is
not set. The master-abort-on-posted-write bit is bit 4 of the P_SERR# event disable register (offset 64h).

Note: When the bridge performs a Type 1 to special cycle conversion, a master abort is the expected
termination for the special cycle on the target bus. In this case, the master abort received bit is not set,
and the Type 1 configuration transaction is disconnected after the first data phase.

2.8.3 TARGET TERMINATION RECEIVED BY PI7C8148A

When the bridge initiates a transaction on the target bus and the target responds with DEVSEL#, the
target can end the transaction with one of the following types of termination:

!

Normal termination (upon de-assertion of FRAME#)

Target retry

Target disconnect

Target abort

The bridge handles these terminations in different ways, depending on the type of transaction being
performed.

2.8.3.1 DELAYED WRITE TARGET TERMINATION RESPONSE

When the bridge initiates a delayed write transaction, the type of target termination received from the
target can be passed back to the initiator. Table 2-7 shows the response to each type of target
termination that occurs during a delayed write transaction.

The bridge repeats a delayed write transaction until one of the following conditions is met:

!

Bridge completes at least one data transfer.

Bridge receives a master abort.

Bridge receives a target abort.

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The bridge makes 2

(default) or 2

(maximum) write attempts resulting in a response of target retry.

Table 2-7. Delayed Write Target Termination Response

Target Termination

Response

Normal

Returning disconnect to initiator with first data transfer only if multiple data phases requested.

Target Retry

Returning target retry to initiator. Continue write attempts to target

Target Disconnect

Returning disconnect to initiator with first data transfer only if multiple data phases requested.

Target Abort

Returning target abort to initiator. Set received target abort bit in target interface status register.
Set signaled target abort bit in initiator interface status register.

After the bridge makes 2

(default) attempts of the same delayed write trans-action on the target bus,

the bridge asserts P_SERR# if the SERR# enable bit (bit 8 of command register for the secondary bus)
is set and the delayed-write-non-delivery bit is not set. The delayed-write-non-delivery bit is bit 5 of
P_SERR# event disable register (offset 64h). The bridge will report system error. See Section 5.4 for a
description of system error conditions.

2.8.3.2 POSTED WRITE TARGET TERMINATION RESPONSE

When the bridge initiates a posted write transaction, the target termination cannot be passed back to the
initiator. Table 2-8 shows the response to each type of target termination that occurs during a posted
write transaction.

Table 2-8. Response to Posted Write Target Termination

Target Termination

Repsonse

Normal

No additional action.

Target Retry

Repeating write transaction to target.

Target Disconnect

Initiate write transaction for delivering remaining posted write data.

Target Abort

Set received-target-abort bit in the target interface status register. Assert
P_SERR# if enabled, and set the signaled-system-error bit in primary status
register.

Note that when a target retry or target disconnect is returned and posted write data associated with that
transaction remains in the write buffers, the bridge initiates another write transaction to attempt to
deliver the rest of the write data. If there is a target retry, the exact same address will be driven as for
the initial write trans-action attempt. If a target disconnect is received, the address that is driven on a
subsequent write transaction attempt will be updated to reflect the address of the current DWORD. If
the initial write transaction is Memory-Write-and-Invalidate transaction, and a partial delivery of write
data to the target is performed before a target disconnect is received, the bridge will use the memory
write command to deliver the rest of the write data. It is because an incomplete cache line will be
transferred in the subsequent write transaction attempt.

After the bridge makes 2

(default) write transaction attempts and fails to deliver all posted write data

associated with that transaction, the bridge asserts P_SERR# if the primary SERR# enable bit is set (bit
8 of command register for secondary bus) and posted-write-non-delivery bit is not set. The posted-
write-non-delivery bit is the bit 2 of P_SERR# event disable register (offset 64h). The bridge will report
system error. See Section 5.4 for a discussion of system error conditions.

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2.8.3.3 DELAYED READ TARGET TERMINATION RESPONSE

When the bridge initiates a delayed read transaction, the abnormal target responses can be passed back
to the initiator. Other target responses depend on how much data the initiator requests. Table 2-9 shows
the response to each type of target termination that occurs during a delayed read transaction.

The bridge repeats a delayed read transaction until one of the following conditions is met:

!

Bridge completes at least one data transfer.

Bridge receives a master abort.

Bridge receives a target abort.

The bridge makes 2

(default) read attempts resulting in a response of target retry.

Table 2-9. Response to Delayed Read Target Termination

Target Termination

Response

Normal

If prefetchable, target disconnect only if initiator requests more data than read from target. If
non-prefetchable, target disconnect on first data phase.

Target Retry

Re-initiate read transaction to target

Target Disconnect

If initiator requests more data than read from target, return target disconnect to initiator.

Target Abort

Return target abort to initiator. Set received target abort bit in the target interface status
register. Set signaled target abort bit in the initiator interface status register.

After the bridge makes 2

(default) attempts of the same delayed read transaction on the target bus, the

bridge asserts P_SERR# if the primary SERR# enable bit is set (bit 8 of command register for
secondary bus) and the delayed-write-non-delivery bit is not set. The delayed-write-non-delivery bit is
bit 5 of P_SERR# event disable register (offset 64h). The bridge will report system error. See Section
5.4 for a description of system error conditions.

2.8.4 TARGET TERMINATION INITIATED BY PI7C8148A

The bridge can return a target retry, target disconnect, or target abort to an initiator for reasons other
than detection of that condition at the target interface.

2.8.4.1 TARGET RETRY

The bridge returns a target retry to the initiator when it cannot accept write data or return read data as a
result of internal conditions. The bridge returns a target retry to an initiator when any of the following
conditions is met:

For delayed write transactions:

!

The transaction is being entered into the delayed transaction queue.

Transaction has already been entered into delayed transaction queue, but target response has not yet

been received.

Target response has been received but has not progressed to the head of the return queue.

The delayed transaction queue is full, and the transaction cannot be queued.

A transaction with the same address and command has been queued.

A locked sequence is being propagated across the bridge, and the write transaction is not a locked

transaction.

The target bus is locked and the write transaction is a locked transaction.

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Use more than 16 clocks to accept this transaction.

For delayed read transactions:

!

The transaction is being entered into the delayed transaction queue.

The read request has already been queued, but read data is not yet available.

Data has been read from target, but it is not yet at head of the read data queue or a posted write
transaction precedes it.

The delayed transaction queue is full, and the transaction cannot be queued.

A delayed read request with the same address and bus command has already been queued.

A locked sequence is being propagated across the bridge, and the read transaction is not a locked
transaction.

The bridge is currently discarding previously pre-fetched read data.

The target bus is locked and the write transaction is a locked transaction.

Use more than 16 clocks to accept this transaction.

For posted write transactions:

!

The posted write data buffer does not have enough space for address and at least one DWORD of

write data.

A locked sequence is being propagated across the bridge, and the write transaction is not a locked

transaction.

When a target retry is returned to the initiator of a delayed transaction, the initiator must repeat the

transaction with the same address and bus command as well as the data if it is a write transaction,
within the time frame specified by the master timeout value. Otherwise, the transaction is discarded
from the buffers.

2.8.4.2 TARGET DISCONNECT

The bridge returns a target disconnect to an initiator when one of the following conditions is met:

!

Bridge hits an internal address boundary.

Bridge cannot accept any more write data.

Bridge has no more read data to deliver.

See Section 2.5.4 for a description of write address boundaries, and Section 2.6.4 for a description of
read address boundaries.

2.8.4.3 TARGET ABORT

The bridge returns a target abort to an initiator when one of the following conditions is met:

!

The bridge is returning a target abort from the intended target.

When the bridge returns a target abort to the initiator, it sets the signaled target abort bit in the

status register corresponding to the initiator interface.

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ADDRESS DECODING

The bridge uses three address ranges that control I/O and memory transaction forwarding. These
address ranges are defined by base and limit address registers in the configuration space. This chapter
describes these address ranges, as well as ISA-mode and VGA-addressing support.

3.1 ADDRESS RANGES

The bridge uses the following address ranges that determine which I/O and memory transactions are
forwarded from the primary PCI bus to the secondary PCI bus, and from the secondary bus to the
primary bus:

!

Two 32-bit I/O address ranges

Two 32-bit memory-mapped I/O (non-prefetchable memory) ranges

Two 32-bit prefetchable memory address ranges

Transactions falling within these ranges are forwarded downstream from the primary PCI bus to the
secondary PCI bus. Transactions falling outside these ranges are forwarded upstream from the
secondary PCI bus to the primary PCI bus.

No address translation is required in the bridge. The addresses that are not marked for downstream are
always forwarded upstream.

3.2 I/O ADDRESS DECODING

The bridge uses the following mechanisms that are defined in the configuration space to specify the I/O
address space for downstream and upstream forwarding:

!

I/O base and limit address registers

The ISA enable bit

The VGA mode bit

The VGA snoop bit

This section provides information on the I/O address registers and ISA mode. Section 3.4 provides
information on the VGA modes.

To enable downstream forwarding of I/O transactions, the I/O enable bit must be set in the command
register in configuration space. All I/O transactions initiated on the primary bus will be ignored if the
I/O enable bit is not set. To enable upstream forwarding of I/O transactions, the master enable bit must
be set in the command register. If the master-enable bit is not set, the bridge ignores all I/O and memory
transactions initiated on the secondary bus.

The master-enable bit also allows upstream forwarding of memory transactions if it is set.

CAUTION
If any configuration state affecting I/O transaction forwarding is changed by a configuration write
operation on the primary bus at the same time that I/O transactions are ongoing on the secondary bus,
the bridge response to the secondary bus I/O transactions is not predictable. Configure the I/O base
and limit address registers, ISA enable bit, VGA mode bit, and VGA snoop bit before setting I/O enable

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and master enable bits, and change them subsequently only when the primary and secondary PCI buses
are idle.

3.2.1 I/O BASE AND LIMIT ADDRESS REGISTER

The bridge implements one set of I/O base and limit address registers in configuration space that define
an I/O address range per port downstream forwarding. The bridge supports 32-bit I/O addressing, which
allows I/O addresses downstream of the bridge to be mapped anywhere in a 4GB I/O address space.

I/O transactions with addresses that fall inside the range defined by the I/O base and limit registers are
forwarded downstream from the primary PCI bus to the secondary PCI bus. I/O transactions with
addresses that fall outside this range are forwarded upstream from the secondary PCI bus to the primary
PCI bus.

The I/O range can be turned off by setting the I/O base address to a value greater than that of the I/O
limit address. When the I/O range is turned off, all I/O trans-actions are forwarded upstream, and no I/O
transactions are forwarded downstream. The I/O range has a minimum granularity of 4KB and is
aligned on a 4KB boundary. The maximum I/O range is 4GB in size. The I/O base register consists of
an 8-bit field at configuration address 1Ch, and a 16-bit field at address 30h. The top 4 bits of the 8-bit
field define bits [15:12] of the I/O base address. The bottom 4 bits read only as 1h to indicate that the
bridge supports 32-bit I/O addressing. Bits [11:0] of the base address are assumed to be 0, which
naturally aligns the base address to a 4KB boundary. The 16 bits contained in the I/O base upper 16 bits
register at configuration offset 30h define AD[31:16] of the I/O base address. All 16 bits are read/write.
After primary bus reset or chip reset, the value of the I/O base address is initialized to 0000 0000h.

The I/O limit register consists of an 8-bit field at configuration offset 1Dh and a 16-bit field at offset
32h. The top 4 bits of the 8-bit field define bits [15:12] of the I/O limit address. The bottom 4 bits read
only as 1h to indicate that 32-bit I/O addressing is supported. Bits [11:0] of the limit address are
assumed to be FFFh, which naturally aligns the limit address to the top of a 4KB I/O address block. The
16 bits contained in the I/O limit upper 16 bits register at configuration offset 32h define AD[31:16] of
the I/O limit address. All 16 bits are read/write. After primary bus reset or chip reset, the value of the
I/O limit address is reset to 0000 0FFFh.

Note: The initial states of the I/O base and I/O limit address registers define an I/O range of 0000 0000h
to 0000 0FFFh, which is the bottom 4KB of I/O space. Write these registers with their appropriate
values before setting either the I/O enable bit or the master enable bit in the command register in
configuration space.

3.2.2 ISA MODE

The bridge supports ISA mode by providing an ISA enable bit in the bridge control register in
configuration space. ISA mode modifies the response of the bridge inside the I/O address range in order
to support mapping of I/O space in the presence of an ISA bus in the system. This bit only affects the
response of the bridge when the transaction falls inside the address range defined by the I/O base and
limit address registers, and only when this address also falls inside the first 64KB of I/O space (address
bits [31:16] are 0000h). When the ISA enable bit is set, the bridge does not forward downstream any
I/O transactions addressing the top 768 bytes of each aligned 1KB block. Only those transactions
addressing the bottom 256 bytes of an aligned 1KB block inside the base and limit I/O address range
are forwarded downstream. Transactions above the 64KB I/O address boundary are forwarded as
defined by the address range defined by the I/O base and limit registers.

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Accordingly, if the ISA enable bit is set, the bridge forwards upstream those I/O transactions addressing
the top 768 bytes of each aligned 1KB block within the first 64KB of I/O space. The master enable bit
in the command configuration register must also be set to enable upstream forwarding. All other I/O
transactions initiated on the secondary bus are forwarded upstream only if they fall outside the I/O
address range.

When the ISA enable bit is set, devices downstream of the bridge can have I/O space mapped into the
first 256 bytes of each 1KB chunk below the 64KB boundary, or anywhere in I/O space above the
64KB boundary.

3.3 MEMORY ADDRESS DECODING

The bridge has three mechanisms for defining memory address ranges for forwarding of memory
transactions:

!

Memory-mapped I/O base and limit address registers

Prefetchable memory base and limit address registers

VGA mode

This section describes the first two mechanisms. Section 3.4.1 describes VGA mode. To enable
downstream forwarding of memory transactions, the memory enable bit must be set in the command
register in configuration space. To enable upstream forwarding of memory transactions, the master-
enable bit must be set in the command register. The master-enable bit also allows upstream forwarding
of I/O transactions if it is set.

CAUTION
If any configuration state affecting memory transaction forwarding is changed by a configuration write
operation on the primary bus at the same time that memory transactions are ongoing on the secondary
bus, response to the secondary bus memory transactions is not predictable. Configure the memory-
mapped I/O base and limit address registers, prefetchable memory base and limit address registers,
and VGA mode bit before setting the memory enable and master enable bits, and change them
subsequently only when the primary and secondary PCI buses are idle.

3.3.1 MEMORY-MAPPED I/O BASE AND LIMIT ADDRESS REGISTERS

Memory-mapped I/O is also referred to as non-prefetchable memory. Memory addresses that cannot
automatically be pre-fetched but that can be conditionally pre-fetched based on command type should
be mapped into this space. Read transactions to non-prefetchable space may exhibit side effects; this
space may have non-memory-like behavior. The bridge prefetches in this space only if the memory
read line or memory read multiple commands are used; transactions using the memory read command
are limited to a single data transfer.

The memory-mapped I/O base address and memory-mapped I/O limit address registers define an
address range that the bridge uses to determine when to forward memory commands. The bridge
forwards a memory transaction from the primary to the secondary interface if the transaction address
falls within the memory-mapped I/O address range. The bridge ignores memory transactions initiated
on the secondary interface that fall into this address range. Any transactions that fall outside this address
range are ignored on the primary interface and are forwarded upstream from the secondary interface
(provided that they do not fall into the prefetchable memory range or are not forwarded downstream by
the VGA mechanism).

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The memory-mapped I/O range supports 32-bit addressing only. The PCI-to-PCI Bridge Architecture
Specification does not provide for 64-bit addressing in the memory-mapped I/O space. The memory-
mapped I/O address range has a granularity and alignment of 1MB. The maximum memory-mapped I/O
address range is 4GB.

The memory-mapped I/O address range is defined by a 16-bit memory-mapped I/O base address
register at configuration offset 20h and by a 16-bit memory-mapped I/O limit address register at offset
22h. The top 12 bits of each of these registers correspond to bits [31:20] of the memory address. The
low 4 bits are hardwired to 0. The lowest 20 bits of the memory-mapped I/O base address are assumed
to be 0 0000h, which results in a natural alignment to a 1MB boundary. The lowest 20 bits of the
memory-mapped I/O limit address are assumed to be FFFFFh, which results in an alignment to the top
of a 1MB block.

Note: The initial state of the memory-mapped I/O base address register is 0000 0000h. The initial state
of the memory-mapped I/O limit address register is 000F FFFFh. Note that the initial states of these
registers define a memory-mapped I/O range at the bottom 1MB block of memory. Write these registers
with their appropriate values before setting either the memory enable bit or the master enable bit in the
command register in configuration space. To turn off the memory-mapped I/O address range, write the
memory-mapped I/O base address register with a value greater than that of the memory-mapped I/O
limit address register.

3.3.2 PREFETCHABLE MEMORY BASE AND LIMIT ADDRESS REGISTERS

Locations accessed in the prefetchable memory address range must have true memory-like behavior and
must not exhibit side effects when read. This means that extra reads to a prefetchable memory location
must have no side effects. The bridge prefetches for all types of memory read commands in this address
space.

The prefetchable memory base address and prefetchable memory limit address registers define an
address range that the bridge uses to determine when to forward memory commands. The bridge
forwards a memory transaction from the primary to the secondary interface if the transaction address
falls within the prefetchable memory address range. The bridge ignores memory transactions initiated
on the secondary interface that fall into this address range. The bridge does not respond to any
transactions that fall outside this address range on the primary interface and forwards those transactions
upstream from the secondary interface (provided that they do not fall into the memory-mapped I/O
range or are not forwarded by the VGA mechanism).

The prefetchable memory range supports 64-bit addressing and provides additional registers to define
the upper 32 bits of the memory address range, the prefetchable memory base address upper 32 bits
register, and the prefetchable memory limit address upper 32 bits register. For address comparison, a
single address cycle (32-bit address) prefetchable memory transaction is treated like a 64-bit address
transaction where the upper 32 bits of the address are equal to 0. This upper 32-bit value of 0 is
compared to the prefetchable memory base address upper 32 bits register and the prefetchable memory
limit address upper 32 bits register. The prefetchable memory base address upper 32 bits register must
be 0 to pass any single address cycle transactions downstream.

Prefetchable memory address range has a granularity and alignment of 1MB. Maximum memory
address range is 4GB when 32-bit addressing is being used. Prefetchable memory address range is
defined by a 16-bit prefetchable memory base address register at configuration offset 24h and by a 16-
bit prefetchable memory limit address register at offset 26h. The top 12 bits of each of these registers
correspond to bits [31:20] of the memory address. The lowest 4 bits are hardwired to 1h. The lowest 20
bits of the prefetchable memory base address are assumed to be 0 0000h, which results in a natural

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alignment to a 1MB boundary. The lowest 20 bits of the prefetchable memory limit address are
assumed to be FFFFFh, which results in an alignment to the top of a 1MB block.

Note: The initial state of the prefetchable memory base address register is 0000 0000h. The initial state
of the prefetchable memory limit address register is 000F FFFFh. Note that the initial states of these
registers define a prefetchable memory range at the bottom 1MB block of memory. Write these
registers with their appropriate values before setting either the memory enable bit or the master enable
bit in the command register in configuration space.

To turn off the prefetchable memory address range, write the prefetchable memory base address register
with a value greater than that of the prefetchable memory limit address register. The entire base value
must be greater than the entire limit value, meaning that the upper 32 bits must be considered.
Therefore, to disable the address range, the upper 32 bits registers can both be set to the same value,
while the lower base register is set greater than the lower limit register. Otherwise, the upper 32-bit base
must be greater than the upper 32-bit limit.

3.4 VGA SUPPORT

The bridge provides two modes for VGA support:

!

VGA mode, supporting VGA-compatible addressing

VGA snoop mode, supporting VGA palette forwarding

3.4.1 VGA MODE

When a VGA-compatible device exists downstream from the bridge, set the VGA mode bit in the
bridge control register in configuration space to enable VGA mode. When the bridge is operating in
VGA mode, it forwards downstream those transactions addressing the VGA frame buffer memory and
VGA I/O registers, regardless of the values of the base and limit address registers. The bridge ignores
transactions initiated on the secondary interface addressing these locations.

The VGA frame buffer consists of the following memory address range:

000A 0000h000B FFFFh

Read transactions to frame buffer memory are treated as non-prefetchable. The bridge requests only a
single data transfer from the target, and read byte enable bits are forwarded to the target bus.

The VGA I/O addresses are in the range of 3B0h3BBh and 3C0h3DFh I/O. These I/O addresses are
aliases every 1KB throughout the first 64KB of I/O space. This means that address bits <15:10> are not
decoded and can be any value, while address bits [31:16] must be all 0's. VGA BIOS addresses starting
at C0000h are not decoded in VGA mode.

3.4.2 VGA SNOOP MODE

The bridge provides VGA snoop mode, allowing for VGA palette write transactions to be forwarded
downstream. This mode is used when a graphics device downstream from the bridge needs to snoop or
respond to VGA palette write transactions. To enable the mode, set the VGA snoop bit in the command

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register in configuration space. Note that the bridge claims VGA palette write transactions by asserting
DEVSEL# in VGA snoop mode.

When VGA snoop bit is set, the bridge forwards downstream transactions within the 3C6h, 3C8h and
3C9h I/O addresses space. Note that these addresses are also forwarded as part of the VGA
compatibility mode previously described. Again, address bits <15:10> are not decoded, while address
bits <31:16> must be equal to 0, which means that these addresses are aliases every 1KB throughout the
first 64KB of I/O space.

Note: If both the VGA mode bit and the VGA snoop bit are set, the bridge behaves in the same way as
if only the VGA mode bit were set.

TRANSACTION ORDERING

To maintain data coherency and consistency, the bridge complies with the ordering rules set forth in the
PCI Local Bus Specification, Revision 2.2, for transactions crossing the bridge. This chapter describes
the ordering rules that control transaction forwarding across the bridge.

4.1 TRANSACTIONS GOVERNED BY ORDERING RULES

Ordering relationships are established for the following classes of transactions crossing the bridge:

Posted write transactions, comprised of memory write and memory write and invalidate
transactions.
Posted write transactions complete at the source before they complete at the destination; that is, data is
written into intermediate data buffers before it reaches the target.

Delayed write request transactions, comprised of I/O write and configuration write transactions.
Delayed write requests are terminated by target retry on the initiator bus and are queued in the delayed
transaction queue. A delayed write transaction must complete on the target bus before it completes on
the initiator bus.

Delayed write completion transactions, comprised of I/O write and configuration write
transactions.
Delayed write completion transactions complete on the target bus, and the target response is queued in
the buffers. A delayed write completion transaction proceeds in the direction opposite that of the
original delayed write request; that is, a delayed write completion transaction proceeds from the target
bus to the initiator bus.

Delayed read request transactions, comprised of all memory read, I/O read, and configuration
read transactions.
Delayed read requests are terminated by target retry on the initiator bus and are queued in the delayed
transaction queue.

Delayed read completion transactions, comprised of all memory read, I/O read, & configuration
read transactions.
Delayed read completion transactions complete on the target bus, and the read data is queued in the read
data buffers. A delayed read completion transaction proceeds in the direction opposite that of the
original delayed read request; that is, a delayed read completion transaction proceeds from the target
bus to the initiator bus.

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The bridge does not combine or merge write transactions:

!

The bridge does not combine separate write transactions into a single write transaction--this

optimization is best implemented in the originating master.

The bridge does not merge bytes on separate masked write transactions to the same DWORD

address--this optimization is also best implemented in the originating master.

The bridge does not collapse sequential write transactions to the same address into a single write

transaction--the PCI Local Bus Specification does not permit this combining of transactions.

4.2 GENERAL ORDERING GUIDELINES

Independent transactions on primary and secondary buses have a relationship only when those
transactions cross the bridge.

The following general ordering guidelines govern transactions crossing the bridge:

!

The ordering relationship of a transaction with respect to other transactions is determined when the

transaction completes, that is, when a transaction ends with a termination other than target retry.

Requests terminated with target retry can be accepted and completed in any order with respect to

other transactions that have been terminated with target retry. If the order of completion of delayed
requests is important, the initiator should not start a second delayed transaction until the first one
has been completed. If more than one delayed transaction is initiated, the initiator should repeat all
delayed transaction requests, using some fairness algorithm. Repeating a delayed transaction cannot
be contingent on completion of another delayed transaction. Otherwise, a deadlock can occur.

Write transactions flowing in one direction have no ordering requirements with respect to write

transactions flowing in the other direction. The bridge can accept posted write transactions on both
interfaces at the same time, as well as initiate posted write transactions on both interfaces at the
same time.

The acceptance of a posted memory write transaction as a target can never be contingent on the

completion of a non-locked, non-posted transaction as a master. This is true for the bridge and must
also be true for other bus agents. Otherwise, a deadlock can occur.

The bridge accepts posted write transactions, regardless of the state of completion of any delayed

transactions being forwarded across the bridge.

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4.3 ORDERING RULES

Table 4-1 shows the ordering relationships of all the transactions and refers by number to the ordering
rules that follow.

Table 4-1. Summary of Transaction Ordering

Pass

Posted Write

Delayed Read
Request

Delayed Write
Request

Delayed Read
Completion

Delayed Write
Completion

Posted Write

Yes

Delayed Read Request

Yes Yes Yes Yes

Delayed Write Request

Yes Yes Yes Yes

Delayed Read
Completion

Yes Yes Yes Yes

Delayed Write
Completion

Yes Yes Yes Yes Yes

Note: The superscript accompanying some of the table entries refers to any applicable ordering rule
listed in this section. Many entries are not governed by these ordering rules; therefore, the
implementation can choose whether or not the transactions pass each other.

The entries without superscripts reflect the bridge's implementation choices.

The following ordering rules describe the transaction relationships. Each ordering rule is followed by an
explanation, and the ordering rules are referred to by number in Table 4-1. These ordering rules apply to
posted write transactions, delayed write and read requests, and delayed write and read completion
transactions crossing the bridge in the same direction. Note that delayed completion transactions cross
the bridge in the direction opposite that of the corresponding delayed requests.

1. Posted write transactions must complete on the target bus in the order in which they were received
on the initiator bus. The subsequent posted write transaction can be setting a flag that covers the data in
the first posted write transaction; if the second transaction were to complete before the first transaction,
a device checking the flag could subsequently consume stale data.

2. A delayed read request traveling in the same direction as a previously queued posted write
transaction must push the posted write data ahead of it. The posted write transaction must complete on
the target bus before the delayed read request can be attempted on the target bus. The read transaction
can be to the same location as the write data, so if the read transaction were to pass the write
transaction, it would return stale data.

3. A delayed read completion must ``pull'' ahead of previously queued posted write data traveling in
the same direction. In this case, the read data is traveling in the same direction as the write data, and the
initiator of the read transaction is on the same side of the bridge as the target of the write transaction.
The posted write transaction must complete to the target before the read data is returned to the initiator.
The read transaction can be a reading to a status register of the initiator of the posted write data and
therefore should not complete until the write transaction is complete.

4. Delayed write requests cannot pass previously queued posted write data. For posted memory write
transactions, the delayed write transaction can set a flag that covers the data in the posted write
transaction. If the delayed write request were to complete before the earlier posted write transaction, a
device checking the flag could subsequently consume stale data.

5. Posted write transactions must be given opportunities to pass delayed read and write requests and
completions. Otherwise, deadlocks may occur when some bridges which support delayed transactions
and other bridges which do not support delayed transactions are being used in the same system. A

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fairness algorithm is used to arbitrate between the posted write queue and the delayed transaction
queue.

4.4 DATA SYNCHRONIZATION

Data synchronization refers to the relationship between interrupt signaling and data delivery. The PCI
Local Bus Specification, Revision 2.2, provides the following alternative methods for synchronizing
data and interrupts:

!

The device signaling the interrupt performs a read of the data just written (software).

The device driver performs a read operation to any register in the interrupting device before

accessing data written by the device (software).

System hardware guarantees that write buffers are flushed before interrupts are forwarded.

The bridge does not have a hardware mechanism to guarantee data synchronization for posted write
transactions. Therefore, all posted write transactions must be followed by a read operation, either from
the device to the location just written (or some other location along the same path), or from the device
driver to one of the device registers.

ERROR HANDLING

The bridge checks, forwards, and generates parity on both the primary and secondary interfaces. To
maintain transparency, the bridge always tries to forward the existing parity condition on one bus to the
other bus, along with address and data. The bridge always attempts to be transparent when reporting
errors, but this is not always possible, given the presence of posted data and delayed transactions.

To support error reporting on the PCI bus, the bridge implements the following:

PERR# and SERR# signals on both the primary and secondary interfaces

Primary status and secondary status registers

The device-specific P_SERR# event disable register

This chapter provides detailed information about how the bridge handles errors. It also describes error
status reporting and error operation disabling.

5.1 ADDRESS PARITY ERRORS

The bridge checks address parity for all transactions on both buses, for all address and all bus
commands. When the bridge detects an address parity error on the primary interface, the following
events occur:

If the parity error response bit is set in the command register, the bridge does not claim the

transaction with P_DEVSEL#; this may allow the transaction to terminate in a master abort. If
parity error response bit is not set, the bridge proceeds normally and accepts the transaction if it
is directed to or across the bridge.

The bridge sets the detected parity error bit in the status register.

The bridge asserts P_SERR# and sets signaled system error bit in the status register, if both the

following conditions are met:

The SERR# enable bit is set in the command register.

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The parity error response bit is set in the command register.

When the bridge detects an address parity error on the secondary interface, the following events occur:

!

If the parity error response bit is set in the bridge control register, the bridge does not claim the

transaction with S_DEVSEL#; this may allow the transaction to terminate in a master abort. If
parity error response bit is not set, the bridge proceeds normally and accepts transaction if it is
directed to or across the bridge.

The bridge sets the detected parity error bit in the secondary status register.

The bridge asserts P_SERR# and sets signaled system error bit in status register, if both of the

following conditions are met:

The SERR# enable bit is set in the command register.

The parity error response bit is set in the bridge control register.

5.2 DATA PARITY ERRORS

When forwarding transactions, the bridge attempts to pass the data parity condition from one interface
to the other unchanged, whenever possible, to allow the master and target devices to handle the error
condition.

The following sections describe, for each type of transaction, the sequence of events that occurs when a
parity error is detected and the way in which the parity condition is forwarded across the bridge.

5.2.1 CONFIGURATION WRITE TRANSACTIONS TO CONFIGURATION

SPACE

When the bridge detects a data parity error during a Type 0 configuration write transaction to the bridge
configuration space, the following events occur:

If the parity error response bit is set in the command register, the bridge asserts P_TRDY# and writes
the data to the configuration register. The bridge also asserts P_PERR#. If the parity error response bit
is not set, the bridge does not assert P_PERR#.

The bridge sets the detected parity error bit in the status register, regardless of the state of the parity
error response bit.

5.2.2 READ TRANSACTIONS

When the bridge detects a parity error during a read transaction, the target drives data and data parity,
and the initiator checks parity and conditionally asserts PERR#. For downstream transactions, when the
bridge detects a read data parity error on the secondary bus, the following events occur:

!

Bridge asserts S_PERR# two cycles following the data transfer, if the secondary interface parity

error response bit is set in the bridge control register.

Bridge sets the detected parity error bit in the secondary status register.

Bridge sets the data parity detected bit in the secondary status register, if the secondary interface

parity error response bit is set in the bridge control register.

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Bridge forwards the bad parity with the data back to the initiator on the primary bus. If the data

with the bad parity is pre-fetched and is not read by the initiator on the primary bus, the data is
discarded and the data with bad parity is not returned to the initiator.

Bridge completes the transaction normally.

For upstream transactions, when the bridge detects a read data parity error on the primary bus, the
following events occur:

!

Bridge asserts P_PERR# two cycles following the data transfer, if the primary interface parity error

response bit is set in the command register.

Bridge sets the detected parity error bit in the primary status register.

Bridge sets the data parity detected bit in the primary status register, if the primary interface parity-

error-response bit is set in the command register.

Bridge forwards the bad parity with the data back to the initiator on the secondary bus. If the data

with the bad parity is pre-fetched and is not read by the initiator on the secondary bus, the data is
discarded and the data with bad parity is not returned to the initiator.

Bridge completes the transaction normally.

The bridge returns to the initiator the data and parity that was received from the target. When the
initiator detects a parity error on this read data and is enabled to report it, the initiator asserts PERR#
two cycles after the data transfer occurs. It is assumed that the initiator takes responsibility for handling
a parity error condition; therefore, when the bridge detects PERR# asserted while returning read data to
the initiator, the bridge does not take any further action and completes the transaction normally.

5.2.3 DELAYED WRITE TRANSACTIONS

When the bridge detects a data parity error during a delayed write transaction, the initiator drives data
and data parity, and the target checks parity and conditionally asserts PERR#.

For delayed write transactions, a parity error can occur at the following times:

!

During the original delayed write request transaction

When the initiator repeats the delayed write request transaction

When the bridge completes the delayed write transaction to the target

When a delayed write transaction is normally queued, the address, command, address parity, data, byte
enable bits, and data parity are all captured and a target retry is returned to the initiator. When the
bridge detects a parity error on the write data for the initial delayed write request transaction, the
following events occur:

!

If the parity-error-response bit corresponding to the initiator bus is set, the bridge asserts TRDY# to

the initiator and the transaction is not queued. If multiple data phases are requested, STOP# is also
asserted to cause a target disconnect. Two cycles after the data transfer, the bridge also asserts
PERR#.

If the parity-error-response bit is not set, the bridge returns a target retry. It queues the transaction

as usual. The bridge does not assert PERR#. In this case, the initiator repeats the transaction.

The bridge sets the detected-parity-error bit in the status register corresponding to the initiator bus,

regardless of the state of the parity-error-response bit.

Note: If parity checking is turned off and data parity errors have occurred for queued or subsequent
delayed write transactions on the initiator bus, it is possible that the initiator's re-attempts of the write
transaction may not match the original queued delayed write information contained in the delayed

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transaction queue. In this case, a master timeout condition may occur, possibly resulting in a system
error (P_SERR# assertion).

For downstream transactions, when the bridge is delivering data to the target on the secondary bus and
S_PERR# is asserted by the target, the following events occur:

!

The bridge sets the secondary interface data parity detected bit in the secondary status register, if

the secondary parity error response bit is set in the bridge control register.

The bridge captures the parity error condition to forward it back to the initiator on the primary bus.

Similarly, for upstream transactions, when the bridge is delivering data to the target on the primary bus
and P_PERR# is asserted by the target, the following events occur:

!

The bridge sets the primary interface data-parity-detected bit in the status register, if the primary

parity-error-response bit is set in the command register.

The bridge captures the parity error condition to forward it back to the initiator on the secondary

bus.

A delayed write transaction is completed on the initiator bus when the initiator repeats the write
transaction with the same address, command, data, and byte enable bits as the delayed write command
that is at the head of the posted data queue. Note that the parity bit is not compared when determining
whether the transaction matches those in the delayed transaction queues.

Two cases must be considered:

!

When parity error is detected on the initiator bus on a subsequent re-attempt of the transaction and

was not detected on the target bus

When parity error is forwarded back from the target bus

For downstream delayed write transactions, when the parity error is detected on the initiator bus and the
bridge has write status to return, the following events occur:

!

Bridge first asserts P_TRDY# and then asserts P_PERR# two cycles later, if the primary interface

parity-error-response bit is set in the command register.

Bridge sets the primary interface parity-error-detected bit in the status register.

Because there was not an exact data and parity match, the write status is not returned and the

transaction remains in the queue.

Similarly, for upstream delayed write transactions, when the parity error is detected on the initiator bus
and the bridge has write status to return, the following events occur:

!

Bridge first asserts S_TRDY# and then asserts S_PERR# two cycles later, if the secondary

interface parity-error-response bit is set in the bridge control register (offset 3Ch).

Bridge sets the secondary interface parity-error-detected bit in the secondary status register.

Because there was not an exact data and parity match, the write status is not returned and the

transaction remains in the queue.

For downstream transactions, where the parity error is being passed back from the target bus and the
parity error condition was not originally detected on the initiator bus, the following events occur:

!

Bridge asserts P_PERR# two cycles after the data transfer, if the following are both true:

The parity-error-response bit is set in the command register of the primary interface.

The parity-error-response bit is set in the bridge control register of the secondary interface.

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Bridge completes the transaction normally.

For upstream transactions, when the parity error is being passed back from the target bus and the parity
error condition was not originally detected on the initiator bus, the following events occur:

!

Bridge asserts S_PERR# two cycles after the data transfer, if the following are both true:

The parity error response bit is set in the command register of the primary interface.

The parity error response bit is set in the bridge control register of the secondary interface.

Bridge completes the transaction normally.

5.2.4 POSTED WRITE TRANSACTIONS

During downstream posted write transactions, when the bridge responds as a target, it detects a data
parity error on the initiator (primary) bus and the following events occur:

!

Bridge asserts P_PERR# two cycles after the data transfer, if the parity error response bit is set in

the command register of primary interface.

Bridge sets the parity error detected bit in the status register of the primary interface.

Bridge captures and forwards the bad parity condition to the secondary bus.

Bridge completes the transaction normally.

Similarly, during upstream posted write transactions, when the bridge responds as a target, it detects a
data parity error on the initiator (secondary) bus, the following events occur:

!

Bridge asserts S_PERR# two cycles after the data transfer, if the parity error response bit is set in

the bridge control register of the secondary interface.

Bridge sets the parity error detected bit in the status register of the secondary interface.

Bridge captures and forwards the bad parity condition to the primary bus.

Bridge completes the transaction normally.

During downstream write transactions, when a data parity error is reported on the target (secondary) bus
by the target's assertion of S_PERR#, the following events occur:

Bridge sets the data parity detected bit in the status register of secondary interface, if the parity

error response bit is set in the bridge control register of the secondary interface.

Bridge asserts P_SERR# and sets the signaled system error bit in the status register, if all the

following conditions are met:

The SERR# enable bit is set in the command register.

The posted write parity error bit of P_SERR# event disable register is not set.

The parity error response bit is set in the bridge control register of the secondary interface.

The parity error response bit is set in the command register of the primary interface.

Bridge has not detected the parity error on the primary (initiator) bus which the parity

error is not forwarded from the primary bus to the secondary bus.

During upstream write transactions, when a data parity error is reported on the target (primary) bus by
the target's assertion of P_PERR#, the following events occur:

!

Bridge sets the data parity detected bit in the status register, if the parity error response bit is set in

the command register of the primary interface.

Bridge asserts P_SERR# and sets the signaled system error bit in the status register, if all the

following conditions are met:

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The SERR# enable bit is set in the command register.

The parity error response bit is set in the bridge control register of the secondary interface.

The parity error response bit is set in the command register of the primary interface.

Bridge has not detected the parity error on the secondary (initiator) bus, which the parity

error is not forwarded from the secondary bus to the primary bus.

Assertion of P_SERR# is used to signal the parity error condition when the initiator does not know that
the error occurred. Because the data has already been delivered with no errors, there is no other way to
signal this information back to the initiator. If the parity error has forwarded from the initiating bus to
the target bus, P_SERR# will not be asserted.

5.3 DATA PARITY ERROR REPORTING SUMMARY

In the previous sections, the responses of the bridge to data parity errors are presented according to the
type of transaction in progress. This section organizes the responses of the bridge to data parity errors
according to the status bits that the bridge sets and the signals that it asserts. Table 5-1 shows setting
the detected parity error bit in the status register, corresponding to the primary interface. This bit is set
when the bridge detects a parity error on the primary interface.

Table 5-1. Setting the Primary Interface Detected Parity Error Bit

Primary Detected
Parity Error Bit

Transaction Type

Direction

Bus Where Error

Was Detected

Primary/ Secondary Parity

Error Response Bits

Read

Downstream

Primary

x / x

Read

Downstream

Secondary

x / x

Read

Upstream

Primary

x / x

Read

Upstream

Secondary

x / x

Posted Write

Downstream

Primary

x / x

Posted Write

Downstream

Secondary

x / x

Posted Write

Upstream

Primary

x / x

Posted Write

Upstream

Secondary

x / x

Delayed Write

Downstream

Primary

x / x

Delayed Write

Downstream

Secondary

x / x

Delayed Write

Upstream

Primary

x / x

Delayed Write

Upstream

Secondary

x / x

= don't care

Table 5-2 shows setting the detected parity error bit in the secondary status register, corresponding to
the secondary interface. This bit is set when the bridge detects a parity error on the secondary interface.

Table 5-2. Setting Secondary Interface Detected Parity Error Bit

Secondary
Detected Parity
Error Bit

Transaction Type

Direction

Bus Where Error

Was Detected

Primary/ Secondary Parity

Error Response Bits

Read

Downstream

Primary

x / x

Read

Downstream

Secondary

x / x

Read

Upstream

Primary

x / x

Read

Upstream

Secondary

x / x

Posted Write

Downstream

Primary

x / x

Posted Write

Downstream

Secondary

x / x

Posted Write

Upstream

Primary

x / x

Posted Write

Upstream

Secondary

x / x

Delayed Write

Downstream

Primary

x / x

Delayed Write

Downstream

Secondary

x / x

Delayed Write

Upstream

Primary

x / x

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Secondary
Detected Parity
Error Bit

Transaction Type

Direction

Bus Where Error

Was Detected

Primary/ Secondary Parity

Error Response Bits

Delayed Write

Upstream

Secondary

x / x

= don't care

Table 5-3 shows setting data parity detected bit in the primary interface's status register. This bit is set
under the following conditions:

!

Bridge must be a master on the primary bus.

The parity error response bit in the command register, corresponding to the primary interface, must

be set.

The P_PERR# signal is detected asserted or a parity error is detected on the primary bus.

Table 5-3. Setting Primary Interface Master Data Parity Error Detected Bit

Primary Data
Parity Bit

Transaction Type

Direction

Bus Where Error

Was Detected

Primary / Secondary Parity

Error Response Bits

Read

Downstream

Primary

x / x

Read

Downstream

Secondary

x / x

Read

Upstream

Primary

1 / x

Read

Upstream

Secondary

x / x

Posted Write

Downstream

Primary

x / x

Posted Write

Downstream

Secondary

x / x

Posted Write

Upstream

Primary

1 / x

Posted Write

Upstream

Secondary

x / x

Delayed Write

Downstream

Primary

x / x

Delayed Write

Downstream

Secondary

x / x

Delayed Write

Upstream

Primary

1 / x

Delayed Write

Upstream

Secondary

x / x

= don't care

Table 5-4 shows setting the data parity detected bit in the status register of secondary interface. This bit
is set under the following conditions:

!

The bridge must be a master on the secondary bus.

The parity error response bit must be set in the bridge control register of secondary interface.

The S_PERR# signal is detected asserted or a parity error is detected on the secondary bus.

Table 5-4. Setting Secondary Interface Master Data Parity Error Detected Bit

Secondary
Detected Parity
Detected Bit

Transaction Type

Direction

Bus Where Error

Was Detected

Primary / Secondary Parity

Error Response Bits

Read

Downstream

Primary

x / x

Read

Downstream

Secondary

x / 1

Read

Upstream

Primary

x / x

Read

Upstream

Secondary

x / x

Posted Write

Downstream

Primary

x / x

Posted Write

Downstream

Secondary

x / 1

Posted Write

Upstream

Primary

x / x

Posted Write

Upstream

Secondary

x / x

Delayed Write

Downstream

Primary

x / x

Delayed Write

Downstream

Secondary

x / 1

Delayed Write

Upstream

Primary

x / x

Delayed Write

Upstream

Secondary

x / x

X= don't care

Table 5-5 shows assertion of P_PERR#. This signal is set under the following conditions:

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The bridge is either the target of a write transaction or the initiator of a read transaction on the

primary bus.

The parity-error-response bit must be set in the command register of primary interface.

The bridge detects a data parity error on the primary bus or detects S_PERR# asserted during the

completion phase of a downstream delayed write transaction on the target (secondary) bus.

Table 5-5. Assertion of P_PERR#

P_PERR# Transaction

Type

Direction

Bus Where Error

Was Detected

Primary/ Secondary Parity

Error Response Bits

1 (de-asserted)

Read

Downstream

Primary

x / x

Read

Downstream

Secondary

x / x

0 (asserted)

Read

Upstream

Primary

1 / x

Read

Upstream

Secondary

x / x

Posted Write

Downstream

Primary

1 / x

Posted Write

Downstream

Secondary

x / x

Posted Write

Upstream

Primary

x / x

Posted Write

Upstream

Secondary

x / x

Delayed Write

Downstream

Primary

1 / x

Delayed Write

Downstream

Secondary

1 / 1

Delayed Write

Upstream

Primary

x / x

Delayed Write

Upstream

Secondary

x / x

= don't care

The parity error was detected on the target (secondary) bus but not on the initiator (primary) bus.

Table 5-6 shows assertion of S_PERR# that is set under the following conditions:

!

The bridge is either the target of a write transaction or the initiator of a read transaction on the

secondary bus.

The parity error response bit must be set in the bridge control register of secondary interface.

Bridge detects a data parity error on the secondary bus or detects P_PERR# asserted during the

completion phase of an upstream delayed write transaction on the target (primary) bus.

Table 5-6. Assertion of S_PERR#

S_PERR# Transaction

Type

Direction

Bus Where Error

Was Detected

Primary/ Secondary Parity

Error Response Bits

1 (de-asserted)

Read

Downstream

Primary

x / x

0 (asserted)

Read

Downstream

Secondary

x / 1

Read

Upstream

Primary

x / x

Read

Upstream

Secondary

x / x

Posted Write

Downstream

Primary

x / x

Posted Write

Downstream

Secondary

x / x

Posted Write

Upstream

Primary

x / x

Posted Write

Upstream

Secondary

x / 1

Delayed Write

Downstream

Primary

x / x

Delayed Write

Downstream

Secondary

x / x

Delayed Write

Upstream

Primary

1 / 1

Delayed Write

Upstream

Secondary

x / 1

= don't care

The parity error was detected on the target (secondary) bus but not on the initiator (primary) bus.

Table 5-7 shows assertion of P_SERR#. This signal is set under the following conditions:

!

The bridge has detected P_PERR# asserted on an upstream posted write transaction or S_PERR#

asserted on a downstream posted write transaction.

The bridge did not detect the parity error as a target of the posted write transaction.

The parity error response bit on the command register and the parity error response bit on the

bridge control register must both be set.

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The SERR# enable bit must be set in the command register.

Table 5-7. Assertion of P_SERR# for Data Parity Errors

P_SERR# Transaction

Type

Direction

Bus Where Error

Was Detected

Primary / Secondary Parity

Error Response Bits

1 (de-asserted)

Read

Downstream

Primary

x / x

Read

Downstream

Secondary

x / x

Read

Upstream

Primary

x / x

Read

Upstream

Secondary

x / x

Posted Write

Downstream

Primary

x / x

(asserted)

Posted Write

Downstream

Secondary

1 / 1

Posted Write

Upstream

Primary

1 / 1

Posted Write

Upstream

Secondary

x / x

Delayed Write

Downstream

Primary

x / x

Delayed Write

Downstream

Secondary

x / x

Delayed Write

Upstream

Primary

x / x

Delayed Write

Upstream

Secondary

x / x

= don't care

The parity error was detected on the target (secondary) bus but not on the initiator (primary) bus.

The parity error was detected on the target (primary) bus but not on the initiator (secondary) bus.

5.4 SYSTEM ERROR (SERR#) REPORTING

The bridge uses the P_SERR# signal to report conditionally a number of system error conditions in
addition to the special case parity error conditions described in Section 5.2.3.

Whenever assertion of P_SERR# is discussed in this document, it is assumed that the following
conditions apply:

!

For the bridge to assert P_SERR# for any reason, the SERR# enable bit must be set in the

command register.

Whenever the bridge asserts P_SERR#, the bridge must also set the signaled system error bit in the

status register.

In compliance with the PCI-to-PCI Bridge Architecture Specification, the bridge asserts P_SERR#
when it detects the secondary SERR# input, S_SERR#, asserted and the SERR# forward enable bit is
set in the bridge control register. In addition, the bridge also sets the received system error bit in the
secondary status register.

The bridge also conditionally asserts P_SERR# for any of the following reasons:

!

Target abort detected during posted write transaction

Master abort detected during posted write transaction

Posted write data discarded after 2

(default) attempts to deliver (2

target retries received)

Parity error reported on target bus during posted write transaction (see previous section)

Delayed write data discarded after 2

(default) attempts to deliver (2

target retries received)

Delayed read data cannot be transferred from target after 2

(default) attempts (2

target retries

received)

Master timeout on delayed transaction

The device-specific P_SERR# status register reports the reason for the assertion of P_SERR#. Most of
these events have additional device-specific disable bits in the P_SERR# event disable register that
make it possible to mask out P_SERR# assertion for specific events. The master timeout condition has a

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SERR# enable bit for that event in the bridge control register and therefore does not have a device-
specific disable bit.

PCI BUS ARBITRATION

The bridge must arbitrate for use of the primary bus when forwarding upstream transactions. Also, it
must arbitrate for use of the secondary bus when forwarding downstream transactions. The arbiter for
the primary bus resides external to the bridge, typically on the motherboard. For the secondary PCI bus,
the bridge implements an internal arbiter. This arbiter can be disabled, and an external arbiter can be
used instead. This chapter describes primary and secondary bus arbitration.

6.1 PRIMARY PCI BUS ARBITRATION

The bridge implements a request output pin, P_REQ#, and a grant input pin, P_GNT#, for primary PCI
bus arbitration. The bridge asserts P_REQ# when forwarding transactions upstream; that is, it acts as
initiator on the primary PCI bus. As long as at least one pending transaction resides in the queues in the
upstream direction, either posted write data or delayed transaction requests, the bridge keeps P_REQ#
asserted. However, if a target retry, target disconnect, or a target abort is received in response to a
transaction initiated by the bridge on the primary PCI bus, the bridge de-asserts P_REQ# for two PCI
clock cycles.

For all cycles through the bridge, P_REQ# is not asserted until the transaction request has been
completely queued. When P_GNT# is asserted LOW by the primary bus arbiter after the bridge has
asserted P_REQ#, the bridge initiates a transaction on the primary bus during the next PCI clock cycle.
When P_GNT# is asserted to the bridge when P_REQ# is not asserted, the bridge parks P_AD, P_CBE,
and P_PAR by driving them to valid logic levels. When the primary bus is parked at the bridge and the
bridge has a transaction to initiate on the primary bus, the bridge starts the transaction if P_GNT# was
asserted during the previous cycle.

6.2 SECONDARY PCI BUS ARBITRATION

The bridge implements an internal secondary PCI bus arbiter. This arbiter supports four external
masters on the secondary bus in addition to the PI7C8148A. The secondary arbiter supports a
programmable 2-level rotating algorithm. If the bridge detects that an initiator has failed to assert
S_FRAME# after 16 cycles of both grant assertion and a secondary idle bus condition, the arbiter de-
asserts the grant.

To prevent bus contention, if the secondary PCI bus is idle, the arbiter never asserts one grant signal in
the same PCI cycle in which it de-asserts another. It de-asserts one grant and asserts the next grant, no
earlier than one PCI clock cycle later. If the secondary PCI bus is busy, that is, S_FRAME# or
S_IRDY# is asserted, the arbiter can be de-asserted one grant and asserted another grant during the
same PCI clock cycle.

6.2.1 PREEMPTION

Preemption can be programmed to be either on or off, with the default to on (offset 4Ch, bit [31:28]).
Time-to-preempt can be programmed to 0, 1, 2, 4, 8, 16, 32, or 64 (default is 0) clocks. If the current

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master occupies the bus and other masters are waiting, the current master will be preempted by
removing its grant (GNT#) after the next master waits for the time-to-preempt.

6.2.2 BUS PARKING

Bus parking refers to driving the AD[31:0], CBE[3:0], and PAR lines to a known value while the bus is
idle. In general, the device implementing the bus arbiter is responsible for parking the bus or assigning
another device to park the bus. A device parks the bus when the bus is idle, its bus grant is asserted, and
the device's request is not asserted. The AD and CBE signals should be driven first, with the PAR
signal driven one cycle later.

The bridge parks the primary bus only when P_GNT# is asserted, P_REQ# is de-asserted, and the
primary PCI bus is idle. When P_GNT# is de-asserted, the bridge 3-states the P_AD, P_CBE, and
P_PAR signals on the next PCI clock cycle. If the bridge is parking the primary PCI bus and wants to
initiate a transaction on that bus, then the bridge can start the transaction on the next PCI clock cycle by
asserting P_FRAME# if P_GNT# is still asserted.

If the internal secondary bus arbiter is enabled, the secondary bus is always parked at the last master
that used the PCI bus. That is, the bridge keeps the secondary bus grant asserted to a particular master
until a new secondary bus request comes along. After reset, the bridge parks the secondary bus at itself
until transactions start occurring on the secondary bus. Offset 48h, bit [1], can be set to 1 to park the
secondary bus at PI7C8148A. By default, offset 48h, bit [1], is set to 0.

CLOCKS

This chapter provides information about the clocks.

7.1 PRIMARY CLOCK INPUTS

The bridge implements a primary clock input for the PCI interface. The primary interface is
synchronized to the primary clock input, P_CLK, and the secondary interface is synchronized to the
secondary clock. In synchronous mode, the secondary clock is derived internally from the primary
clock, P_CLK. The bridge operates at a maximum frequency of 66 MHz.

7.2 SECONDARY CLOCK OUTPUTS

The bridge has 4 secondary clock outputs, S_CLKOUT[3:0] that can be used as clock inputs for up to
four external secondary bus devices. The S_CLKOUT[3:0] outputs are derived from P_CLK. The
secondary clock edges are delayed from P_CLK edges by a minimum of 0ns.

7.3 PCI CLOCKRUN

The bridge supports the PCI clock run protocol defined in the PCI Mobile Design Guide 1.0.
P_CLKRUN# is set HIGH when the system's central resource initiates to stop the primary clock
(P_CLK). The bridge will then signal that it allows the PCI clock to be stopped by keeping

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P_CLKRUN# HIGH, or it will initiate P_CLK to remain running by driving P_CLKRUN# LOW for 2
clocks. After the 2 clocks have elapsed, the system's central resource will keep P_CLKRUN# LOW.
There are 3 conditions where the bridge will keep the primary clock running:

!

Bit [26] offset 6Ch is set to 1

There is a pending transaction running through the bridge

A secondary device requires the clock

The secondary clock run protocol is enabled by bit [25] offset 6Ch. The primary is responsible for the
initiation of stopping or slowing down the secondary clock. The exception to this is if bit[28] offset
6Ch is set to 1. In this situation, the secondary clock will be stopped when the bus is idle and there are
no other cycles from the primary bus.

GENERAL PURPOSE I/O INTERFACE

The PI7C8148A implements a 4-pin general purpose I/O interface. During normal operation, device
specific configuration registers control the GPIO interface.

8.1 GPIO CONTROL REGISTERS

During normal operation, the GPIO Control Register (bits[23:8] offset C4h) controls the GPIO
interface.

Each GPIO pin can be configured to be either an input or an output pin. All GPIO pins can be read or
written to at any time using either a type 0 configuration read or type 0 configuration write. Please see
section 15.2.55 for more information on the GPIO Control Register.

EEPROM INTERFACE

The EEPROM interface consists of two pins: EECLK (EEPROM clock output) and EEPD (EEPROM
bi-directional serial data). The bridge may control an ISSI IS24C02 or compatible part, which is
organized into 256x8 bits. The EEPROM is used to initialize a select number of registers. This is
accomplished after PRST# is deasserted, at which time the data from the EEPROM will be loaded. The
EEPROM interface is organized into a 16-bit base, and the bridge supplies a 7-bit EEPROM word
address. The bridge does not control the EEPROM address input. It can only access the EEPROM
with address input set to 0.

9.1 AUTO MODE EEPROM ACCESS

The bridge may access the EEPROM in a WORD format by utilizing the auto mode through a hardware
sequencer. The EEPROM start control, address, and read/write commands can be accessed through the
configuration register. Before each access, the software should check the Start EEPROM bit before
issuing the next start.

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9.2 EEPROM MODE AT RESET

During a reset, the bridge will autoload information/data from the EEPROM if the automatic load
condition is met. The first offset in the EEPROM contains a signature. If the signature is recognized, the
autoload will initiate right after the reset.

During the autoload, the bridge will read sequential words from the EEPROM and write to the
appropriate registers. Before the bridge registers can be accessed through the host, the autoload
condition should be verified by reading bit[3] offset C8h (EEPROM Autoload Success). The host
access is allowed only after the status of this bit becomes '1' which signifies that the autoload
initialization sequence has completed successfully.

9.3 EEPROM DATA STRUCTURE

The bridge will access the EEPROM one WORD at a time. The bit order during the address phase is
reverse that of the data phase. The data order starts with the MSB to the LSB during the address phase,
but starts with the LSB to the MSB during the data phase.

9.4 EEPROM SPACE ADDRESS MAP

15 8

7 - 0

WORD ADDRESS

EEPROM Signature (1516h)

00h

Secondary Clock Enable

Region Enable

02h

Subsystem Vendor ID

04h

Subsystem ID

06h

Test Mode / Chip Control / ISA Enable

Arbiter Control

08h

Vendor ID

0Ah

Device ID

0Ch

Secondary Bus Arbiter Pre-emption Control

Extended Chip Control

0Eh

Power Management Capability

10h

PM Data Register

Reserved

12h

Port Option

14h

9.4.1 EEPROM CONTENT

Address

PCI Configuration

Offset

Description

1:0

8148 EEPROM Signature

Autoload will only proceed if a value of 1516h is read on the first WORD loaded.
Any other value read will disable the autoload.

Region Enable Enables or disables certain regions of the configuration space
register from being loaded by the EEPROM

Bit[0]: Reserved

Bit[4:1]: 0000 stop autoload at address 02h

0001 stop autoload at address 04h

0011 stop autoload at address 07h

0111 stop autoload at address 11h

1111 autoload all EEPROM loadable registers

others combinations are undefined

Bit[7:5]: Reserved

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Address

PCI Configuration

Offset

Description

68h

68h Bit[1:0]
68h Bit[3:2]
68h Bit[5:4]
68h Bit[7:6]
68h Bit[8]

Secondary Clock Enable Provides a means to disable the secondary clocks

Bit[0]: set, S_CLKOUT[0] disable
Bit[1]: set, S_CLKOUT[1] disable
Bit[2]: set, S_CLKOUT[2] disable
Bit[3]: set, S_CLKOUT[3] disable
Bit[4]: set, S_CLKOUT[4] disable
Bit[7:5]: Reserved

5:4

F0 F1h

Subsystem Vendor ID

7:6

F2 F3h

Subsystem ID

40h

40h Bit[16]
40h Bit[17]
40h Bit[18]
40h Bit[19]

40h Bit[25]

Arbiter Control

Bit[0]: set, S_REQ#[0] will be HIGH priority on the secondary bus
Bit[1]: set, S_REQ#[1] will be HIGH priority on the secondary bus
Bit[2]: set, S_REQ#[2] will be HIGH priority on the secondary bus
Bit[3]: set, S_REQ#[3] will be HIGH priority on the secondary bus
Bit[6:4]: Reserved
Bit[7]: set, Bridge port will be HIGH priority on the secondary bus

C0h, 40h

C0h Bit[8]

40h Bit[1]
40h Bit[4]

40h Bit[9]
40h Bit[11:10]

40h Bit[12]

Test Mode / Chip Control / ISA Enable

Bit[0]: set, legacy ISA I/O enable
Bit[1]: Reserved
Bit[2]: set, memory write disconnects at cache line aligned address boundary
Bit[3]: set, bridge requests only 1 DWORD from the target and forwards read

byte enable bits during upstream memory read

Bit[4]: set, minimum 1 free space in data FIFO to accept memory burst write
Bit[6:5]: Bridge Behavior Control

00 Enable the out of transaction order between all 4 DTR requests

01 Accept 3 DTR requests simultaneously and they may be out of
transaction order

10 Only the 2 DTR requests at the top of the 2 FIFO's may be
allowed to out of transaction order

11 No out of order transactions allowed for all DTR requests

Bit[7]: set, 2 memory write transactions can be accepted at a time

0B:0A

00 01h

Vendor ID

0D:0C

02 03h

Device ID

48h

48h Bit[0]
48h Bit[1]
48h Bit[2]
48h Bit[3]
48h Bit[4]

Extended Chip Control

Bit[0]: set, memory read flow through enable
Bit[1]: set, park to bridge port on secondary bus
Bit[2]: set, downstream memory read prefetching dynamic control disable
Bit[3]: set, upstream memory read prefetching dynamic control disable
Bit[4]: set, memory read underflow control
Bit[7:5]: Reserved

4Ch

4Ch Bit[31:28]

Secondary Bus Arbiter Pre-emption Control

Bit[3:0]: Reserved
Bit[7:4]: Controls the number of clock cycles after FRAME is asserted before
pre-emption is enabled
1xxx Pre-emption off
0000 Pre-emption enabled after 0 clock cycles after FRAME asserted
0001 Pre-emption enabled after 1 clock cycle after FRAME asserted
0010 Pre-emption enabled after 2 clock cycles after FRAME asserted
0011 - Pre-emption enabled after 4 clock cycles after FRAME asserted
0100 Pre-emption enabled after 8 clock cycles after FRAME asserted
0101 Pre-emption enabled after 16 clock cycles after FRAME asserted
0110 Pre-emption enabled after 32 clock cycles after FRAME asserted
0111 Pre-emption enabled after 64 clock cycles after FRAME asserted

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Address

PCI Configuration

Offset

Description

80h

80h Bit[18:16]

80h Bit[21]

80h Bit[25]
80h Bit[26]

80h Bit[31:27]

Power Management Capability

Bit[2:0]: read only as 010 to indicate the device is compliant to Revision 1.1 of

PCI Power Management Interface Specifications

Bit[4:3]: Reserved
Bit[5]: read only as 0 to indicate bridge does not have device specific utilization

requirements

Bit[8:6]: Reserved
Bit[9]: read only as 1 to indicate bridge supports the D1 power management state
Bit[10]: read only as 1 to indicate bridge supports the D2 power management

state

Bit[14:11]: read only as 0 to indicate bridge does not support the PME# pin
Bit[15]: Reserved

Reserved

84h

84h Bit[31:24]

Power Management Data

Bit[15:8]: read only as Data Register

74h

Port Option Register

Bit[0]: Reserved
Bit[1]: set, primary memory read command alias enable
Bit[2]: set, primary memory write command alias enable
Bit[3]: set, secondary memory read command alias enable
Bit[4]: set, secondary memory write command alias enable
Bit[5]: set, primary memory read line/multiple alias enable
Bit[6]: set, secondary memory read line/multiple alias enable
Bit[7]: set, primary memory write & invalidate command alias disable
Bit[8]: set, secondary memory write & invalidate command alias disable
Bit[9]: set, enable long request for LOCK cycle
Bit[10]: set, enable secondary to hold request longer
Bit[11]: set, enable primary to hold request longer
Bit[15:12]: Reserved

10 COMPACT PCI HOT SWAP

Compact PCI (cPCI) Hot Swap (PICMG 2.1, R1.0) defines a process for installing and removing PCI
boards form a Compact PCI system without powering down the system. The PI7C8148A is Hot Swap
Friendly silicon that supports all the cPCI Hot Swap Capable features and adds support for Software
Connection Control. Being Hot Swap Friendly, the bridge supports the following:

!

Compliance with PCI Specification 2.2

Tolerates V

from Early Power

Asynchronous Reset

Tolerates Precharge Voltage

I/O Buffers Meet Modified V/I Requirements

Limited I/O Pin Leakage at Precharge Voltage

The bridge provides two pins to support hot swap: ENUM# and LOO. The ENUM# output indicates to
the system that an insertion event occurred or that an extraction is about to occur. The LOO output
lights an LED to signal insertion- and removal-ready status.

11 PCI POWER MANAGEMENT

The bridge

incorporates functionality that meets the requirements of the PCI Power Management

Specification, Revision 1.1. These features include:

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PCI Power Management registers using the Enhanced Capabilities Port (ECP) address mechanism

Support for D0, D3

hot

and D3

cold

power management states

Support for D0, D1, D2, D3

hot

, and D3

cold

power management states for devices behind the bridge

Support of the B2 secondary bus power state when in the D3

hot

power management state

Table 11-1

shows the states and related actions that the bridge performs during power management

transitions. (No other transactions are permitted.)

Table 11-1. Power Management Transitions

Current Status

Next State

Action

D3cold

Power has been removed from bridge. A power-up reset must be performed to
bring bridge to D0.

D3hot

If enabled to do so by the BPCCE pin, bridge will disable the secondary clocks
and drive them LOW.

Unimplemented power state. bridge will ignore the write to the power state
bits (power state remains at D0).

D3hot

Bridge enables secondary clock outputs and performs an internal chip reset.
Signal S_RST# will not be asserted. All registers will be returned to the reset
values and buffers will be cleared.

D3hot

D3cold

Power has been removed from bridge. A power-up reset must be performed to
bring bridge to D0.

D3cold

Power-up reset. Bridge performs the standard power-up reset functions as
described in Section 12.

PME# signals are routed from downstream devices around PCI-to-PCI bridges. PME# signals do not
pass through PCI-to-PCI bridges.

12 RESET

This chapter describes the primary interface, secondary interface, and chip reset mechanisms.

12.1 PRIMARY INTERFACE RESET

The bridge has a reset input, P_RST#. When P_RST# is asserted, the following events occur:

!

Bridge immediately tri-states all primary and secondary PCI interface signals.

Bridge performs a chip reset.

Registers that have default values are reset.

P_RST# asserting and de-asserting edges can be asynchronous to P_CLK and S_CLKOUT. The bridge
is not accessible during P_RST#. After P_RST# is de-asserted, the bridge remains inaccessible for 16
PCI clocks before the first configuration transaction can be accepted.

12.2 SECONDARY INTERFACE RESET

The bridge is responsible for driving the secondary bus reset signals, S_RST#. The bridge asserts
S_RST# when any of the following conditions are met:

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Signal P_RST# is asserted. Signal S_RST# remains asserted as long as P_RST# is asserted and does
not de-assert until P_RST# is de-asserted.

The secondary reset bit in the bridge control register is set. Signal S_RST# remains asserted until a
configuration write operation clears the secondary reset bit.

S_RST# pin is asserted. When S_RST# is asserted, the bridge immediately 3-states all the secondary
PCI interface signals associated with the secondary port. The S_RST# in asserting and de-asserting
edges can be asynchronous to P_CLK.

When S_RST# is asserted, all secondary PCI interface control signals, including the secondary grant
outputs, are immediately 3-stated. Signals S1_AD, S1_CBE#[3:0], S_PAR are driven low for the
duration of S_RST# assertion. All posted write and delayed transaction data buffers are reset.
Therefore, any transactions residing inside the buffers at the time of secondary reset are discarded.

When S_RST# is asserted by means of the secondary reset bit, the bridge remains accessible during
secondary interface reset and continues to respond to accesses to its configuration space from the
primary interface.

12.3 CHIP RESET

The chip reset bit in the diagnostic control register can be used to reset the bridge and the secondary
bus.

When the chip reset bit is set, all registers and chip state are reset and all signals are tristated. S_RST#
is asserted and the secondary reset bit is automatically set. S_RST# remains asserted until a
configuration write operation clears the secondary reset bit and the serial clock mask has been shifted
in. Within 20 PCI clock cycles after completion of the configuration write operation, the bridge's reset
bit automatically clears and the bridge is ready for configuration.

During reset, the bridge is inaccessible.

13 SUPPORTED COMMANDS

The PCI command set is given below for the primary and secondary interfaces.

13.1 PRIMARY INTERFACE

P_CBE [3:0]

Command

Action

0000 Interrupt

Acknowledge

Ignore

0001

Special Cycle

Do not claim. Ignore.

0010

I/O Read

1. If address is within pass through I/O range, claim and pass through.

2. Otherwise, do not pass through and do not claim for internal access.

0011

I/O Write

Same as I/O Read.

0100 Reserved

-----

0101 Reserved

-----

0110

Memory Read

1. If address is within pass through memory range, claim and pass
through.

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P_CBE [3:0]

Command

Action

2. If address is within pass through memory mapped I/O range, claim and
pass through.

3. Otherwise, do not pass through and do not claim for internal access.

0111

Memory Write

Same as Memory Read.

1000 Reserved

-----

1001 Reserved

-----

1010 Configuration

Read

Type 0 Configuration Read:
If the bridge's IDSEL line is asserted, perform function decode and claim
if target function is implemented. Otherwise, ignore. If claimed, permit
access to target function's configuration registers. Do not pass through
under any circumstances.

Type 1 Configuration Read:
1. If the target bus is the bridge's secondary bus: claim and pass through
as a Type 0 Configuration Read.

2. If the target bus is a subordinate bus that exists behind the bridge (but
not equal to the secondary bus): claim and pass through as a Type 1
Configuration Read.

3. Otherwise, ignore.

1011 Configuration

Write

Type 0 Configuration Write: same as Configuration Read.

Type 1 Configuration Write (not special cycle request):
1. If the target bus is the bridge's secondary bus: claim and pass through
as a Type 0 Configuration Write

2. If the target bus is a subordinate bus that exists behind the bridge (but
not equal to the secondary bus): claim and pass through unchanged as a
Type 1 Configuration Write.

3. Otherwise, ignore.

Configuration Write as Special Cycle Request
(device = 1Fh, function = 7h)
1. If the target bus is the bridges secondary bus: claim and pass through
as a special cycle.

2. If the target bus is a subordinate bus that exists behind the bridge (but
not equal to the secondary bus): claim and pass through unchanged as a
type 1 Configuration Write.

3. Otherwise ignore

1100 Memory

Read

Multiple

Same as Memory Read

1101

Dual Address Cycle

Supported

1110

Memory Read Line

Same as Memory Read

1111

Memory Write and
Invalidate

Same as Memory Read

13.2 SECONDARY INTERFACE

S_CBE[3:0] Command

Action

0000 Interrupt

Acknowledge

Ignore

0001

Special Cycle

Do not claim. Ignore.

0010

I/O Read

Same as Primary Interface

0011

I/O Write

Same as I/O Read.

0100 Reserved

-----

0101 Reserved

-----

0110

Memory Read

Same as Primary Interface

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S_CBE[3:0] Command

Action

0111

Memory Write

Same as Memory Read.

1000 Reserved

-----

1001 Reserved

-----

1010 Configuration

Read

Ignore

1011 Configuration

Write

I. Type 0 Configuration Write: Ignore

II. Type 1 Configuration Write (not special cycle request):Ignore

III. Configuration Write as Special Cycle Request (device = 1Fh,
function = 7h):
1. If the target bus is the bridge's primary bus: claim and pass through as
a Special Cycle

2. If the target bus is neither the primary bus nor is it in range of buses
defined by the bridge's secondary and subordinate bus registers: claim
and pass through unchanged as a Type 1 Configuration Write.

3. If the target bus is not the bridge's primary bus, but is in range of buses
defined by the bridge's secondary and subordinate bus registers: ignore.

1100 Memory

Read

Multiple

Same as Memory Read

1101

Dual Address Cycle

Supported

1110

Memory Read Line

Same as Memory Read

1111 Memory

Write

and

Invalidate

Same as Memory Read

14 BRIDGE BEHAVIOR

A PCI cycle is initiated by asserting the FRAME# signal. In a bridge, there are a number of
possibilities. Those possibilities are summarized in the table below:

14.1 BRIDGE ACTIONS FOR VARIOUS CYCLE TYPES

Initiator Target Response
Master on Primary

Target on Primary

Bridge does not respond. It detects this situation by
decoding the address as well as monitoring the
P_DEVSEL# for other fast and medium devices on the
Primary Port.

Master on Primary

Target on Secondary

Bridge asserts P_DEVSEL#, terminates the cycle
normally if it is able to be posted, otherwise return
with a retry. It then passes the cycle to the appropriate
port. When the cycle is complete on the target port, it
will wait for the initiator to repeat the same cycle and
end with normal termination.

Master on Primary

Target not on Primary nor
Secondary Port

Bridge does not respond and the cycle will terminate
as master abort.

Master on Secondary

Target on the same
Secondary Port

Bridge does not respond.

Master on Secondary

Target on Primary or the
other Secondary Port

Bridge asserts S_DEVSEL#, terminates the cycle
normally if it is able to be posted, otherwise returns
with a retry. It then passes the cycle to the appropriate
port. When cycle is complete on the target port, it will
wait for the initiator to repeat the same cycle and end
with normal termination.

Master on Secondary

Target not on Primary nor
the other Secondary Port

Bridge does not respond.

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14.2 ABNORMAL TERMINATION (INITIATED BY BRIDGE

MASTER)

14.2.1 MASTER ABORT

Master abort indicates that when the bridge acts as a master and receives no response (i.e., no target
asserts DEVSEL# or S_DEVSEL#) from a target, the bridge de-asserts FRAME# and then deasserts
IRDY#.

14.2.2 PARITY AND ERROR REPORTING

Parity must be checked for all addresses and write data. Parity is defined on the P_PAR, and S_PAR
signals. Parity should be even (i.e. an even number of`1's) across AD, CBE, and PAR. Parity
information on PAR is valid the cycle after AD and CBE are valid. For reads, even parity must be
generated using the initiators CBE signals combined with the read data. Again, the PAR signal
corresponds to read data from the previous data phase cycle.

14.2.3 REPORTING PARITY ERRORS

For all address phases, if a parity error is detected, the error should be reported on the P_SERR# signal
by asserting P_SERR# for one cycle and then 3-stating two cycles after the bad address. P_SERR# can
only be asserted if bit 6 and 8 in the Command Register are both set to 1. For write data phases, a parity
error should be reported by asserting the P_PERR_L signal two cycles after the data phase and should
remain asserted for one cycle when bit 6 in the Command register is set to a 1. The target reports any
type of data parity errors during write cycles, while the master reports data parity errors during read
cycles.

Detection of an address parity error will cause the PCI-to-PCI Bridge target to not claim the bus
(P_DEVSEL# remains inactive) and the cycle will then terminate with a Master Abort. When the bridge
is acting as master, a data parity error during a read cycle results in the bridge master initiating a Master
Abort.

14.2.4 SECONDARY IDSEL MAPPING

When the bridge detects a Type 1 configuration transaction for a device connected to the secondary, it
translates the Type 1 transaction to Type 0 transaction on the downstream interface. Type 1
configuration format uses a 5-bit field at P_AD[15:11] as a device number. This is translated to
S_AD[31:16] by the bridge.

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15 CONFIGURATION REGISTERS

PCI configuration defines a 64-byte DWORD to define various attributes of PI7C8148A as shown
below.

15.1 REGISTER TYPES

REGISTER TYPE

DEFINITION

RO Read

Only

Read / Write

RWC

Read / Write 1 to Clear

RWR

Read / Write 1 to Reset (for about 20 clocks)

RWS

Read / Write 1 to Set

15.2 CONFIGURATION REGISTER

31 24

23 16

15 8

7 0

DWORD ADDRESS

Device ID

Vendor ID

00h

Primary Status

Command

04h

Class Code

Revision ID

08h

Reserved Header

Type

Primary Latency

Timer

Cache Line Size

0Ch

Reserved

10h 14h

Secondary Latency

Timer

Subordinate Bus

Number

Secondary Bus

Number

Primary Bus

Number

18h

Secondary Status

I/O Limit Address

I/O Base Address

1Ch

Memory Limit Address

Memory Base Address

20h

Prefetchable Memory Limit Address

Prefetchable Memory Base Address

24h

Prefetchable Memory Base Address Upper 32-bit

28h

Prefetchable Memory Limit Address Upper 32-bit

2Ch

I/O Limit Address Upper 16-bit

I/O Base Address Upper 16-bit

30h

Reserved Capability

Pointer

34h

Reserved 38h

Bridge Control

Interrupt Pin

Reserved

3Ch

Arbiter Control

Diagnostic / Chip Control

40h

Reserved 44h

Reserved

Extended Chip Control

48h

Secondary Bus

Arbiter Preemption

Control

Reserved 4Ch

Reserved

50h 60h

Reserved

P_SERR# Event

Disable

64h

Reserved

P_SERR# Status

Secondary Clock Control

68h

CLKRUN Reserved

6Ch

Reserved 70h

Reserved Port

Option

74h

Reserved

78h 7Ch

Power Management Capabilities

Next Item Pointer

Capability ID

80h

PM Data

PPB Support

Extensions

Power Management Data

84h

Secondary Master Timeout Counter

Primary Master Timeout Counter

88h

Reserved 8Ch

Reserved

HSCSR

Next Item Pointer

Capability ID

90h

Reserved

Hot Swap Switch

94h

Reserved

98h 9Fh

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VPD Register

Next Item Pointer

Capability ID

A0h

VPD Data Register

A4h

Reserved

A8h BFh

Reserved

Miscellaneous

Control

Reserved C0h

Reserved GPIO

Control

Reserved

C4h

EEPROM Data

EEPROM Address

EEPROM Control

C8h

EEPROM Test

Reserved CCh

Reserved

D0h Efh

Subsystem ID

Subsystem Vendor ID

F0h

Reserved

F4h - FFh

15.2.1 VENDOR ID REGISTER OFFSET 00h

Bit Function

Type

Description

15:0

Vendor ID

Identifies Pericom as the vendor of this device. Hardwired as 12D8h.

15.2.2 DEVICE ID REGISTER OFFSET 00h

Bit Function

Type

Description

31:16

Device ID

Identifies this device as the PI7C8148A. Reset to 8148h.

15.2.3 COMMAND REGISTER OFFSET 04h

Bit Function

Type

Description

I/O Space
Enable

0: ignore I/O transactions on the primary interface

1: enable response to I/O transactions on the primary interface

Reset to 0

Memory Space
Enable

0: ignore memory transactions on the primary interface

1: enable response to memory transactions on the primary interface

Reset to 0

Bus Master
Enable

0: do not initiate memory or I/O transactions on the primary interface and disable
response to memory and I/O transactions on the secondary interface

1: enables bridge to operate as a master on the primary interfaces for memory and
I/O transactions forwarded from the secondary interface

Reset to 0

Special Cycle
Enable

No special cycles defined.
Bit is defined as read only and returns 0 when read

Memory Write
And Invalidate
Enable

Bridge does not generate memory write and invalidate transactions except for
forwarding a transaction for another master.

Bit is implemented as read only and returns 0 when read (unless forwarding a
transaction for another master)

VGA Palette
Snoop Enable

0: ignore VGA palette accesses on the primary

1: enable positive decoding response to VGA palette writes on the primary
interface with I/O address bits AD[9:0] equal to 3C6h, 3C8h, and 3C9h (inclusive
of ISA alias; AD[15:10] are not decoded and may be any value)

Reset to 0

Parity Error

0: bridge may ignore any parity errors that it detects and continue normal

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Bit Function

Type

Description

Response operation

1: bridge must take its normal action when a parity error is detected

Reset to 0

Wait Cycle
Control

Read as 0 to indicate PI7C8148A does not perform address / data stepping.

Reset to 0

P_SERR#
enable

0: disable the P_SERR# driver

1: enable the P_SERR# driver

Reset to 0

Fast Back-to-
Back Enable

0: disable bridge's ability to initiate fast back-to-back transactions on the primary

1: enable bridge's ability to initiate fast back-to-back transactions on the primary

Reset to 0

15:10

Reserved

Returns 000000 when read

15.2.4 PRIMARY STATUS REGISTER OFFSET 04h

Bit Function

Type

Description

19:16

Reserved

Reset to 0000

20 Capabilities

List

Set to 1 to enable support for the capability list (offset 34h is the pointer to the
data structure)

Reset to 1

21 66MHz

Capable

Set to 1 to indicate the primary may be run at 66MHz operation

Reset to 1

Reserved

Reset to 0

23 Fast

Back-to-

Back Capable

Set to 1 to enable decoding of fast back-to-back transactions on the primary
interface to different targets

Reset to 1

24 Data

Parity

Error Detected

RWC

0: No parity error detected on the primary (bridge is the primary bus master)

1: Parity error detected on the primary (bridge is the primary bus master)

Reset to 0

26:25 DEVSEL#

timing

DEVSEL# timing (medium decoding)

01: medium DEVSEL# decoding

Reset to 01

27 Signaled

Target

Abort

RWC

Set to 1 (by a target device) whenever a target abort cycle occurs

Reset to 0

28 Received

Target Abort

RWC

Set to 1 (by a master device) whenever transactions are terminated with target
aborts

Reset to 0

29 Received

Master Abort

RWC

Set to 1 (by a master) when transactions are terminated with Master Abort

Reset to 0

30 Signaled

System Error

RWC

Set to 1 when P_SERR# is asserted

Reset to 0

31 Detected

Parity

Error

RWC

Set to 1 when address or data parity error is detected on the primary interface

Reset to 0

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15.2.5 REVISION ID REGISTER OFFSET 08h

Bit Function

Type

Description

7:0

Revision

Indicates revision number of device. Hardwired to 00h

15.2.6 CLASS CODE REGISTER OFFSET 08h

Bit Function

Type

Description

15:8 Programming

Interface

Read as 00h to indicate no programming interfaces have been defined for PCI-to-
PCI bridges

23:16

Sub-Class Code

Read as 04h to indicate device is PCI-to-PCI bridge

31:24 Base

Class

Code

Read as 06h to indicate device is a bridge device

15.2.7 CACHE LINE REGISTER OFFSET 0Ch

Bit Function

Type

Description

7:0 Cache

Line

Size

Designates the cache line size for the system and is used when terminating
memory write and invalidate transactions and when prefetching memory read
transactions.
Only cache line sizes (in units of 4-byte) which are a power of two are valid (only
one bit can be set in this register; only 00h, 01h, 02h, 04h, 08h, and 10h are valid
values).

Reset to 0

15.2.8 PRIMARY LATENCY TIMER REGISTER OFFSET 0Ch

Bit Function

Type

Description

15:8 Primary

Latency timer

This register sets the value for the Master Latency Timer, which starts counting
when the master asserts FRAME#.

Reset to 0

15.2.9 HEADER TYPE REGISTER OFFSET 0Ch

Bit Function

Type

Description

23:16

Header Type

Read as 01h to indicate that the register layout conforms to the standard PCI-to-
PCI bridge layout.

15.2.10 PRIMARY BUS NUMBER REGISTER OFFSET 18h

Bit Function

Type

Description

7:0 Primary

Bus

Number

Indicates the number of the PCI bus to which the primary interface is connected.
The value is set in software during configuration.

Reset to 0

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15.2.11 SECONDARY BUS NUMBER REGISTER OFFSET 18h

Bit Function

Type

Description

15:8 Secondary

Bus

Number

Indicates the number of the PCI bus to which the secondary interface is
connected. The value is set in software during configuration.

Reset to 0

15.2.12 SUBORDINATE BUS NUMBER REGISTER OFFSET 18h

Bit Function

Type

Description

23:16 Subordinate

Bus Number

Indicates the number of the PCI bus with the highest number that is subordinate to
the bridge. The value is set in software during configuration.

Reset to 0

15.2.13 SECONDARY LATENCY TIMER REGISTER OFFSET 18h

Bit Function

Type

Description

31:24 Secondary

Latency Timer

Latency timer for secondary. Indicates the number of PCI clocks from the
assertion of S_FRAME# to the expiration of the timer when the bridge is acting
as a master on the secondary.

0: Bridge ends the transaction after the first data transfer when the bridge's
secondary bus grant has been deasserted, with the exception of memory write and
invalidate transactions.

Reset to 0

15.2.14 I/O BASE ADDRESS REGISTER OFFSET 1Ch

Bit Function

Type

Description

3:0

32-bit Indicator

Read as 01h to indicate 32-bit I/O addressing

7:4 I/O

Base

Address [15:12]

Defines the bottom address of the I/O address range for the bridge to determine
when to forward I/O transactions from one interface to the other. The upper 4 bits
correspond to address bits [15:12] and are writable. The lower 12 bits
corresponding to address bits [11:0] are assumed to be 0. The upper 16 bits
corresponding to address bits [31:16] are defined in the I/O base address upper 16
bits address register

Reset to 0

15.2.15 I/O LIMIT ADDRESS REGISTER OFFSET 1Ch

Bit Function

Type

Description

11:8

32-bit Indicator

Read as 01h to indicate 32-bit I/O addressing

15:12 I/O

Limit

Address
[15:12]

Defines the top address of the I/O address range for the bridge to determine when
to forward I/O transactions from one interface to the other. The upper 4 bits
correspond to address bits [15:12] and are writable. The lower 12 bits
corresponding to address bits [11:0] are assumed to be FFFh. The upper 16 bits
corresponding to address bits [31:16] are defined in the I/O limit address upper 16
bits address register

Reset to 0

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15.2.16 SECONDARY STATUS REGISTER OFFSET 1Ch

Bit Function

Type

Description

20:16

Reserved

Reset to 0

21 66MHz

Capable

Set to 1 to indicate bridge is capable of 66MHz operation on the secondary
interface

Reset to 1

Reserved

Reset to 0

Fast Back-to-
Back Capable

Set to 1 to indicate bridge is capable of decoding fast back-to-back transactions
on the secondary interface to different targets

Reset to 1

Data Parity
Error Detected

RWC

Set to 1 when S_PERR# is asserted and bit 6 of command register is set

Reset to 0

26:25

DEVSEL_L
timing

DEVSEL# timing (medium decoding)

01: medium DEVSEL# decoding

Reset to 01

Signaled Target
Abort

RWC

Set to 1 (by a target device) whenever a target abort cycle occurs on its secondary
interface

Reset to 0

Received
Target Abort

RWC

Set to 1 (by a master device) whenever transactions on its secondary interface are
terminated with target abort

Reset to 0

Received
Master Abort

RWC

Set to 1 (by a master) when transactions on its secondary interface are terminated
with Master Abort

Reset to 0

Received
System Error

RWC

Set to 1 when S_SERR# is asserted

Reset to 0

Detected Parity
Error

RWC

Set to 1 when address or data parity error is detected on the secondary interface

Reset to 0

15.2.17 MEMORY BASE ADDRESS REGISTER OFFSET 20h

Bit Function

Type

Description

3:0

Reserved

Reset to 0

15:4 Memory

Base

Address [15:4]

Defines the bottom address of an address range for the bridge to determine when
to forward memory transactions from one interface to the other. The upper 12
bits correspond to address bits [31:20] and are writable. The lower 20 bits
corresponding to address bits [19:0] are assumed to be 0.

Reset to 0

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15.2.18 MEMORY LIMIT ADDRESS REGISTER OFFSET 20h

Bit Function

Type

Description

19:16

Reserved

Reset to 0

31:20 Memory

Limit

Address [31:20]

Defines the top address of an address range for the bridge to determine when to
forward memory transactions from one interface to the other. The upper 12 bits
correspond to address bits [31:20] and are writable. The lower 20 bits
corresponding to address bits [19:0] are assumed to be FFFFFh.

15.2.19 PREFETCHABLE MEMORY BASE ADDRESS REGISTER OFFSET 24h

Bit Function

Type

Description

3:0 64-bit

addressing

Indicates 64-bit addressing

0001: 64-bit addressing

Reset to 1

15:4 Prefetchable

Memory Base
Address [31:20]

Defines the bottom address of an address range for the bridge to determine when
to forward memory read and write transactions from one interface to the other.
The upper 12 bits correspond to address bits [31:20] and are writable. The lower
20 bits are assumed to be 0. The memory base register upper 32 bits contains the
upper half of the base address.

15.2.20 PREFETCHABLE MEMORY LIMIT ADDRESS REGISTER OFFSET 24h

Bit Function

Type

Description

19:16 64-bit

addressing

Indicates 64-bit addressing

0001: 64-bit addressing

Reset to 1

31:20 Prefetchable

Memory Limit
Address [31:20]

Defines the top address of an address range for the bridge to determine when to
forward memory read and write transactions from one interface to the other. The
upper 12 bits correspond to address bits [31:20] and are writable. The lower 20
bits are assumed to be FFFFFh. The memory limit upper 32 bits register contains
the upper half of the limit address.

15.2.21 PREFETCHABLE MEMORY BASE ADDRESS UPPER 32-BITS REGISTER

 OFFSET 28h

Bit Function

Type

Description

31:0 Prefetchable

Memory Base
Address, Upper
32-bits [63:32]

Defines the upper 32-bits of a 64-bit bottom address of an address range for the
bridge to determine when to forward memory read and write transactions from
one interface to the other.

Reset to 0

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15.2.22 PREFETCHABLE MEMORY LIMIT ADDRESS UPPER 32-BITS REGISTER

 OFFSET 2Ch

Bit Function

Type

Description

31:0 Prefetchable

Memory Limit
Address, Upper
32-bits [63:32]

Defines the upper 32-bits of a 64-bit top address of an address range for the
bridge to determine when to forward memory read and write transactions from
one interface to the other.

Reset to 0

15.2.23 I/O BASE ADDRESS UPPER 16-BITS REGISTER OFFSET 30h

Bit Function

Type

Description

15:0 I/O

Base

Address, Upper
16-bits [31:16]

Defines the upper 16-bits of a 32-bit bottom address of an address range for the
bridge to determine when to forward I/O transactions from one interface to the
other.

Reset to 0

15.2.24 I/O LIMIT ADDRESS UPPER 16-BITS REGISTER OFFSET 30h

Bit Function

Type

Description

31:16 I/O

Limit

Address, Upper
16-bits [31:16]

Defines the upper 16-bits of a 32-bit top address of an address range for the
bridge to determine when to forward I/O transactions from one interface to the
other.

Reset to 0

15.2.25 CAPABILITY POINTER REGISTER OFFSET 34h

Bit Function

Type

Description

7:0 Capability

Pointer

Pointer points to the PCI power management registers (80h).

Reset to 80h

15.2.26 INTERRUPT LINE REGISTER OFFSET 3Ch

Bit Function

Type

Description

7:0

Interrupt Line

Bridge does not implement an interrupt signal, so POST programs FFh to this
register.

15.2.27 INTERRUPT PIN REGISTER OFFSET 3Ch

Bit Function

Type

Description

15:8

Interrupt Pin

Bridge does not implement interrupt signal pins.

Reset to 0

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15.2.28 BRIDGE CONTROL REGISTER OFFSET 3Ch

Bit Function

Type

Description

16 Parity

Error

Response

0: ignore address and data parity errors on the secondary interface

1: enable parity error reporting and detection on the secondary interface

Reset to 0

17 S_SERR#

enable

0: disable the forwarding of S_SERR# to primary interface

1: enable the forwarding of S_SERR# to primary interface

Reset to 0

ISA enable

Modifies the bridge's response to ISA I/O addresses, applying only to those
addresses falling within the I/O base and limit address registers and within the
first 64KB of PCI I/O space.

0: forward all I/O addresses in the range defined by the I/O base and I/O limit
registers

1: blocks forwarding of ISA I/O addresses in the range defined by the I/O base
and I/O limit registers that are in the first 64KB of I/O space that address the last
768 bytes in each 1KB block. Secondary I/O transactions are forwarded upstream
if the address falls within the last 768 bytes in each 1KB block

Reset to 0

VGA enable

0: does not forward VGA compatible memory and I/O addresses from primary to
secondary

1: forward VGA compatible memory and I/O addresses from primary to
secondary regardless of other settings

Reset to 0

Reserved

R/O

Reserved. Returns 0 when read. Reset to 0

21 Master

Abort

Mode

0: does not report master aborts (returns FFFF_FFFFh on reads and discards data
on writes)

1: reports master aborts by signaling target abort if possible or by the assertion of
P_SERR# if enabled

Reset to 0

22 Secondary

Interface Reset

0: does not force the assertion of S_RESET# pin

1: forces the assertion of S_RESET#

Reset to 0

23 Fast

Back-to-

Back Enable

Controls bridge's ability to generate fast back-to-back transactions to different
devices on the secondary interface.

0: does not generate fast back-to-back transactions on the secondary

1: enables fast back-to-back transaction generation on the secondary

Reset to 0

24 Primary

Master

Timeout

R/W

Determines the maximum number of PCI clock cycles the bridge waits for an
initiator on the primary interface to repeat a delayed transaction request.

0: Primary discard timer counts 2

PCI clock cycles.

1: Primary discard timer counts 2

PCI clock cycles.

Reset to 0

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Bit Function

Type

Description

25 Secondary

Master Timeout

Determines the maximum number of PCI clock cycles the bridge waits for an
initiator on the secondary interface to repeat a delayed transaction request.

0: Secondary discard timer counts 2

PCI clock cycles.

1: Secondary discard timer counts 2

PCI clock cycles.

Reset to 0

26 Master

Timeout

Status

RWC

This bit is set to 1 when either the primary master timeout counter or secondary
master timeout counter expires.

Reset to 0

27 Discard

Timer

P_SERR#
enable

This bit is set to 1 and P_SERR# is asserted when either the primary discard timer
or the secondary discard timer expire.

0: P_SERR# is not asserted on the primary interface as a result of the expiration
of either the Primary Discard Timer or the Secondary Discard Timer.

1: P_SERR# is asserted on the primary interface as a result of the expiration of
either the Primary Discard Timer or the Secondary Discard Timer.

Reset to 0

31-28

Reserved

Reserved. Returns 0 when read. Reset to 0.

15.2.29 DIAGNOSTIC/CHIP CONTROL REGISTER OFFSET 40h

Bit Function

Type

Description

0 Reserved RO

Reserved.

Returns 0 when read. Reset to 0

1 Memory

Write

Disconnect

0: Memory write disconnects at 4KB aligned address boundary

1: Memory write disconnects at cache line aligned address boundary

Reset to 0

3:2 Reserved

RO Reserved.

Returns 00 when read. Reset to 00

4 Secondary

Bus

Prefetch
Disable

0: Bridge prefetches and does not forward byte enable bits during upstream
memory read

1: Bridge requests only 1 DWORD from the target and forwards read byte enable
bits during upstream memory read

Reset to 0

7:5 Reserved

RO Reserved.

Returns 00 when read. Reset to 00

Chip Reset

RWR

0: Bridge is ready for operation

1: Forces Bridge to do a reset

Reset to 0

Test Mode 1:
Bridge behavior
control

0: Minimum 8 free spaces in data FIFO to accept memory burst writes

1: Minimum 1 free space in data FIFO to accept memory burst writes

Reset to 0

11:10

Test Mode 2:
Bridge behavior
control

00: Enable the out of transaction order between all 4 DTR requests

01: Accept 3 DTR requests simultaneously and they may be out of transaction
order

10: Only the 2 DTR requests at the top of the 2 FIFO's may be allowed to be out
of transaction order

11: No out of order transactions allowed for all DTR requests.

Reset to 00

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Bit Function

Type

Description

Test Mode 3:
Bridge behavior
control

0: 4 memory write transactions may be accepted at a time

1: 2 memory write transactions may be accepted at a time

Reset to 0

15:13

Reserved

Reserved. Returns 000 when read. Reset to 000

15.2.30 ARBITER CONTROL REGISTER OFFSET 40h

Bit Function

Type

Description

16 S_REQ#[0]

priority

S_REQ#[0] priority on secondary bus

0: low priority
1: high priority

Reset to 0

17 S_REQ#[1]

priority

S_REQ#[1] priority on secondary bus

0: low priority
1: high priority

Reset to 0

18 S_REQ#[2]

priority

S_REQ#[2] priority on secondary bus

0: low priority
1: high priority

Reset to 0

19 S_REQ#[3]

priority

S_REQ#[3] priority on secondary bus

0: low priority
1: high priority

Reset to 0

24:20 Reserved

RO Reserved.

Returns 00000 when read. Reset to 00000

25 HPG_SM,

bridge port

Secondary REQ priority

0: low priority
1: high priority

Reset to 1

31:26 Reserved

RO Reserved.

Returns 0 when read. Reset to 0

15.2.31 EXTENDED CHIP CONTROL REGISTER OFFSET 48h

Bit Function

Type

Description

Memory Read
Flow Through
Enable

0: Disable flow through during a memory read transaction

1: Enable flow through during a memory read transaction

Reset to 0

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Bit Function

Type

Description

1 Park

Controls bus arbiter's park function

0: Park to last master

1: Park to the bridge secondary port

Reset to 0

Downstream
Dynamic
Prefetching
Control

Controls the downstream (P to S) memory read line and memory read multiple
prefetching dynamic control

0: Enable the downstream memory read line and memory read multiple
prefetching dynamic control

1: Disable the downstream memory read line and memory read multiple
prefetching dynamic control

Reset to 0

Upstream
Dynamic
Prefetching
Control

Controls the upstream (S to P) memory read line and memory read multiple
prefetching dynamic control

0: Enable the upstream memory read line and memory read multiple prefetching
dynamic control

1: Disable the upstream memory read line and memory read multiple prefetching
dynamic control

Reset to 0

Memory Read
Data Buffer
Control

Ability to control bridge's behavior when the data buffer is empty

0: start returning memory read data right away and inserts wait states if the data
buffer is empty

1: start returning memory read data after 1 cache line of data and disconnects the
master if the data buffer is empty

Reset to 0

15:5

Reserved

Reserved. Returns 0 when read. Reset to 0

15.2.32 SECONDARY BUS ARBITER PREEMPTION CONTROL REGISTER 

OFFSET 4Ch

Bit Function

Type

Description

31:28

Secondary bus
arbiter
preemption
control

Controls the number of clock cycles after frame is asserted before preemption is
enabled.

1xxx: Preemption off

0000: Preemption enabled after 0 clock cycles after FRAME asserted

0001: Preemption enabled after 1 clock cycle after FRAME asserted

0010: Preemption enabled after 2 clock cycles after FRAME asserted

0011: Preemption enabled after 4 clock cycles after FRAME asserted

0100: Preemption enabled after 8 clock cycles after FRAME asserted

0101: Preemption enabled after 16 clock cycles after FRAME asserted

0110: Preemption enabled after 32 clock cycles after FRAME asserted

0111: Preemption enabled after 64 clock cycles after FRAME asserted

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15.2.33 P_SERR# EVENT DISABLE REGISTER OFFSET 64h

Bit Function

Type

Description

Reserved

Reserved. Returns 0 when read. Reset to 0

Posted Write
Parity Error

Controls bridge's ability to assert P_SERR# when it is unable to transfer any read
data from the target after 2

attempts.

0: P_SERR# is asserted if this event occurs and the SERR# enable bit in the
command register is set.

1: P_SERR# is not asserted if this event occurs.

Reset to 0

Posted Write
Non-Delivery

Controls bridge's ability to assert P_SERR# when it is unable to transfer delayed
write data after 2

attempts.

0: P_SERR# is asserted if this event occurs and the SERR# enable bit in the
command register is set

1: P_SERR# is not asserted if this event occurs

Reset to 0

Target Abort
During Posted
Write

Controls bridge's ability to assert P_SERR# when it receives a target abort when
attempting to deliver posted write data.

0: P_SERR# is asserted if this event occurs and the SERR# enable bit in the
command register is set

1: P_SERR# is not asserted if this event occurs

Reset to 0

Master Abort
On Posted
Write

Controls bridge's ability to assert P_SERR# when it receives a master abort when
attempting to deliver posted write data.

0: P_SERR# is asserted if this event occurs and the SERR# enable bit in the
command register is set

1: P_SERR# is not asserted if this event occurs

Reset to 0

Delayed Write
Non-Delivery

Controls bridge's ability to assert P_SERR# when it is unable to transfer delayed
write data after 2

attempts.

0: P_SERR# is asserted if this event occurs and the SERR# enable bit in the
command register is set

1: P_SERR# is not asserted if this event occurs

Reset to 0

Delayed Read
No Data From
Target

Controls bridge's ability to assert P_SERR# when it is unable to transfer any read
data from the target after 2

attempts.

0: P_SERR# is asserted if this event occurs and the SERR# enable bit in the
command register is set

1: P_SERR# is not asserted if this event occurs

Reset to 0

Reserved

Reserved. Returns 0 when read. Reset to 0

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15.2.34 SECONDARY CLOCK CONTROL REGISTER OFFSET 68h

Bit Function

Type

Description

1:0

S_CLKOUT[0]
disable

S_CLKOUT[0] (slot 0) Enable

00: enable S_CLKOUT[0]
01: enable S_CLKOUT[0]
10: enable S_CLKOUT[0]
11: disable S_CLKOUT[0] and driven LOW

Reset to 00

3:2

Clock 1 disable

S_CLKOUT[1] (slot 1) Enable

00: enable S_CLKOUT[1]
01: enable S_CLKOUT[1]
10: enable S_CLKOUT[1]
11: disable S_CLKOUT[1] and driven LOW

Reset to 00

5:4

Clock 2 disable

S_CLKOUT[2] (slot 2) Enable

00: enable S_CLKOUT[2]
01: enable S_CLKOUT[2]
10: enable S_CLKOUT[2]
11: disable S_CLKOUT[2] and driven LOW

Reset to 00

7:6

Clock 3 disable

S_CLKOUT[3] (slot 3) Enable

00: enable S_CLKOUT[3]
01: enable S_CLKOUT[3]
10: enable S_CLKOUT[3]
11: disable S_CLKOUT[3] and driven LOW

Reset to 00

Clock 4 disable

S_CLKOUT[4] (device 1) clock enable

0: enable S_CLKOUT[4]
1: disable S_CLKOUT[4] and driven LOW

Reset to 0

13:9 Reserved

RO Reserved. Reset to 1Fh

15:14 Reserved

RO Reserved. Reset to 00

15.2.35 P_SERR# STATUS REGISTER OFFSET 68h

Bit Function

Type

Description

Address Parity
Error

RWC

1: Signal P_SERR# was asserted because an address parity error was detected on
P or S bus.

Reset to 0

Posted Write
Data Parity
Error

RWC

1: Signal P_SERR# was asserted because a posted write data parity error was
detected on the target bus.

Reset to 0

Posted Write
Non-delivery

RWC

1: Signal P_SERR# was asserted because the bridge was unable to deliver post
memory write data to the target after 2

attempts.

Reset to 0

Target Abort
during Posted
Write

RWC

1: Signal P_SERR# was asserted because the bridge received a target abort when
delivering post memory write data.

Reset to 0.

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Bit Function

Type

Description

Master Abort
during Posted
Write

RWC

1: Signal P_SERR# was asserted because the bridge received a master abort when
attempting to deliver post memory write data

Reset to 0.

Delayed Write
Non-delivery

RWC

1: Signal P_SERR# was asserted because the bridge was unable to deliver
delayed write data after 2

attempts.

Reset to 0

Delayed Read
No Data from
Target

RWC

1: Signal P_SERR# was asserted because the bridge was unable to read any data
from the target after 2

attempts.

Reset to 0.

Delayed
Transaction
Master Timeout

RWC

1: Signal P_SERR# was asserted because a master did not repeat a read or write
transaction before master timeout.

Reset to 0.

15.2.36 CLKRUN REGISTER OFFSET 6Ch

Bit Function

Type

Description

Secondary
Clock Stop
Status

0: Secondary clock not stopped

1: Secondary clock stopped.

Reset to 0

Secondary
CLKRUN
Enable

0: Disable secondary CLKRUN

1: Enable secondary CLKRUN

Reset to 0

Primary Clock
Stop

0: Allow primary clock to stop if secondary clock is stopped

1: Always keep primary clock running

Reset to 0

Primary
CLKRUN
Enable

0: Disable primary CLKRUN

1: Enable primary CLKRUN

Reset to 0

CLKRUN
mode

0: Stop the secondary clock only on request from the primary bus

1: Stop the secondary clock whenever the secondary bus is idle and there are no
requests from the primary bus

Reset to 0

31:29

Reserved

Reserved. Reset to 0.

15.2.37 PORT OPTION REGISTER OFFSET 74h

Bit Function

Type

Description

Reserved

Reserved. Reset to 0

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Bit Function

Type

Description

Primary
Memory Read
Command
Alias Enable

Controls bridge's detection mechanism for matching memory read retry cycles
from the initiator on the primary interface

0: exact matching memory read retry cycles from initiator on the primary
interface

1: alias MEMRL or MEMRM to MEMR for memory read retry cycles from the
initiator on the primary interface

Reset to 1

Primary
Memory Write
Command
Alias Enable

Controls bridge's detection mechanism for matching non-posted memory write
retry cycles from the initiator on the primary interface

0: exact matching for non-posted memory read retry cycles from initiator on the
primary interface

1: alias MEMWI to MEMW for non-posted memory read retry cycles from
initiator on the primary interface

Reset to 0

Secondary
Memory Read
Command
Alias Enable

Controls bridge's detection mechanism for matching memory read retry cycles
from the initiator on the secondary

0: exact matching for memory read retry cycles from initiator on the secondary
interface

1: alias MEMRL or MEMRM to MEMR for memory read retry cycles from
initiator on the secondary interface

Reset to 1

Secondary
Memory Write
Command
Alias Enable

Controls bridge's detection mechanism for matching non-posted memory write
retry cycles from the initiator on the primary interface

0: exact matching for non-posted memory write retry cycles from initiator on the
secondary interface

1: alias MEMWI to MEMW for non-posted memory write retry cycles from
initiator on the secondary interface

Reset to 0

Primary
Memory Read
Line/Multiple
Alias Enable

Control's bridge's detection mechanism for matching memory read line/multiple
cycles from the initiator on the primary interface

0: exact matching for memory read line/multiple retry cycles from the initiator on
the primary interface

1: alias MEMRL to MEMRM or MEMRM to MEMRL for memory read retry
cycles from the initiator on the primary interface

Reset to 1

Secondary
Memory Read
Line/Multiple
Alias Enable

Control's bridge's detection mechanism for matching memory read line/multiple
cycles from the initiator on the secondary interface

0: exact matching for memory read line/multiple retry cycles from the initiator on
the secondary interface

1: alias MEMRL to MEMRM or MEMRM to MEMRL for memory read retry
cycles from the initiator on the secondary interface

Reset to 1

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Bit Function

Type

Description

Primary
Memory Write
and Invalidate
Command
Alias Disable

Controls bridge's detection mechanism for matching non-posted memory write
and invalidate cycles from the initiator on the primary interface

0: When accepting MEMWI command at the primary interface, bridge converts
MEMWI to MEMW command on the destination interface

1: When accepting MEMWI command at the primary interface, bridge does not
convert MEMWI to MEMW command on the destination interface

Reset to 0

Secondary
Memory Write
and Invalidate
Command
Alias Disable

Controls bridge's detection mechanism for matching non-posted memory write
and invalidate cycles from the initiator on the secondary interface

0: When accepting MEMWI command at the secondary interface, bridge converts
MEMWI to MEMW command on the destination interface

1: When accepting MEMWI command at the secondary interface, bridge does not
convert MEMWI to MEMW command on the destination interface

Reset to 0

Enable Long
Request

Controls bridge's ability to enable long requests for lock cycles

0: normal lock operation

1: enable long request for lock cycle

Reset to 0

Enable
Secondary To
Hold Request
Longer

Control's bridge's ability to enable the secondary bus to hold requests longer.

0: internal secondary master will release REQ# after FRAME# assertion

1: internal secondary master will hold REQ# until there is no transactions pending
in FIFO or until terminated by target

Reset to 1

Enable Primary
To Hold
Request Longer

Control's bridge's ability to hold requests longer at the Primary Port.

0: internal Primary master will release REQ# after FRAME# assertion

1: internal Primary master will hold REQ# until there is no transactions pending
in FIFO or until terminated by target

Reset to 1

15:12

Reserved

Reserved. Returns 0 when read. Reset to 0.

15.2.38 CAPABILITY ID REGISTER OFFSET 80h

Bit Function

Type

Description

7:0

Enhanced
Capabilities ID

Read as 01h to indicate that these are power management enhanced capability
registers.

15.2.39 NEXT ITEM POINTER REGISTER OFFSET 80h

Bit Function

Type

Description

15:8

Next Item
Pointer

Read as 90h. Pointer points to the Hot Swap Capability Register.

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15.2.40 POWER MANAGEMENT CAPABILITIES REGISTER OFFSET 80h

Bit Function

Type

Description

18:16

Power
Management
Revision

Read as 010 to indicate the device is compliant to Revision 1.1 of PCI Power
Management Interface Specifications.

PME# Clock

Read as 0 to indicate bridge does not support the PME# pin.

Auxiliary
Power

Read as 0 to indicate bridge does not support the PME# pin or an auxiliary power
source.

Device Specific
Initialization

Read as 0 to indicate bridge does not have device specific initialization
requirements.

24:22

Reserved

Read as 0

D1 Power State
Support

Read as 1 to indicate bridge supports the D1 power management state.

D2 Power State
Support

Read as 1 to indicate bridge supports the D2 power management state.

31:27

PME# Support

Read as 0 to indicate bridge does not support the PME# pin.

15.2.41 POWER MANAGEMENT DATA REGISTER OFFSET 84h

Bit Function

Type

Description

1:0 Power

State RW

Indicates the current power state of the bridge. If an unimplemented power state
is written to this register, the bridge completes the write transaction, ignores the
write data, and does not change the value of the field. Writing a value of D0
when the previous state was D3 cause a chip reset without asserting S_RESET#

00: D0 state
01: D1 state
10: D2 state
11: D3 state

Reset to 0

7:2

Reserved

Read as 0

PME# Enable

Read as 0 as the bridge does not support the PME# pin.

12:9

Data Select

Read as 0 as the data register is not implemented.

14:13

Data Scale

Read as 0 as the data register is not implemented.

PME status

Read as 0 as the PME# pin is not implemented.

15.2.42 PPB SUPPORT EXTENSIONS OFFSET 84h

Bit Function

Type

Description

21:16 Reserved

RO Reserved.

Returns 0 when read. Reset to 0

B2_B3 Support
for D3

HOT

0: when BPCCE pin is tied LOW

1: when BPCEE pin is tied HIGH, driving secondary clock outputs LOW

Bus Power /
Clock Control
Enable

0: when BPCCE pin is tied LOW

1: when BPCCE pin is tied HIGH

15.2.43 DATA REGISTER OFFSET 84h

Bit Function

Type

Description

31:24 Data

Data Register.

Reset to 0

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

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15.2.44 PRIMARY MASTER TIMEOUT COUNTER REGISTER OFFSET 88h

Bit Function

Type

Description

15:0

Primary
Timeout

Primary timeout occurs after 2

PCI clocks.

Reset to 8000h.

15.2.45 SECONDARY MASTER TIMEOUT COUNTER REGISTER OFFSET 88h

Bit Function

Type

Description

31:16

Secondary
Timeout

Secondary timeout occurs after 2

PCI clocks.

Reset to 8000h.

15.2.46 CAPABILITY ID REGISTER OFFSET 90h

Bit Function

Type

Description

7:0

Enhanced
Capabilities ID

Read as 06h to indicate that these are power management enhanced capability
registers.

15.2.47 NEXT ITEM POINTER REGISTER OFFSET 90h

Bit Function

Type

Description

15:8

Next Item
Pointer

Read as A0h. Pointer points to the VPD Capability Register.

15.2.48 HOT SWAP CAPABILITY STRUCTURE REGISTER OFFSET 90h

Bit Function

Type

Description

Device Hide
Active

0: Device is not hidden and PCI transactions are allowed during extraction state

1: Device is hidden and PCI transactions are not allowed during extraction state

Reset to 0

ENUM# Signal
Mask

0: Enable ENUM# signal

1: Mask ENUM# signal

Reset to 0

Reserved

Reserved. Reset to 0

19 LED

On/Off RW

0: LED off

1: LED on

Reset to 1

21:20

Reserved

Reserved. Reset to 00

Extraction
Status

RWC

Assertion of ENUM# based on a device being extracted

0: ENUM# asserted

1: ENUM# not asserted

Reset to 0

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

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Bit Function

Type

Description

23 Insertion

Status

RWC

Assertion of ENUM# based on a device being inserted

0: ENUM# not asserted

1: ENUM# asserted

Reset to 0

15.2.49 HOT SWAP SWITCH REGISTER OFFSET 94h

Bit Function

Type

Description

Soft Hot Swap
Extraction
Switch

0: Pending extraction of board

1: Board is in the inserted state

7:1

Reserved

Reserved. Reset to 0.

15.2.50 VPD CAPABILITY ID REGISTER OFFSET A0h

Bit Function

Type

Description

7:0

Enhanced
Capabilities ID

Read as 03h to indicate that these are VPD enhanced capability registers.

15.2.51 NEXT ITEM POINTER REGISTER OFFSET A0h

Bit Function

Type

Description

15:8

Next Item
Pointer

Read as 0h. No other ECP registers.

15.2.52 VPD REGISTER OFFSET A0h

Bit Function

Type

Description

17:16

Reserved

Read as 00

23:18 VPD

Address RW

Contains the DWORD address that is used to generate read or write cycles to the
VPD tables store in the EEPROM

30:24

Reserved

Read as 0

31 VPD

Operation

0: Performs VPD read command to VPD table at the location as specified in the
VPD address. This bit is kept "0" and then set to "1" automatically after the
EEPROM cycle is finished.

1: Performs VPD write command to VPD table at the location as specified in the
VPD address. This bit is kept "1" and then set to "0" automatically after the
EERPOM cycled is finished.

Reset to 0

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15.2.53 VPD DATA REGISTER OFFSET A4h

Bit Function

Type

Description

31:0 VPD

Data

For reads, it returns the last data read from the VPD table at the location as
specified in the VPD address.

For writes, it places the current data in to the VPD table at the location as
specified in the VPD address.

15.2.54 MISCELLANEOUS CONTROL REGISTER OFFSET C0h

Bit Function

Type

Description

Legacy ISA I/O
Enable

0: The following I/O addresses will not be claimed by the bridge and will not be
forwarded on to the secondary bus

1: The following I/O addresses will be forwarded on to the secondary bus

Game port: 0200h 0207h
FM: 0388h 038bh
Audio: 0220h 0233h
MIDI: 0330h 0331h

Reset to 0

15:9

Reserved

Reserved. Reset to 0

15.2.55 GPIO CONTROL REGISTER OFFSET C4h

Bit Function

Type

Description

7:0 Reserved

RO Reserved.

Returns 00 when read. Reset to 00

GPIO[0] Input

State of GPIO[0] pin

GPIO[0]
Output Enable

0: GPIO[0] is an input pin

1: GPIO[0] is an output pin

Reset to 0

GPIO[0]
Output Register

Value of this bit will be output to GPIO[0] pin if GPIO[0] is configured as an
output pin

Reset to 0

11 Reserved

RO Reserved

GPIO[1] Input

State of GPIO[1] pin

GPIO[1]
Output Enable

0: GPIO[1] is an input pin

1: GPIO[1] is an output pin

Reset to 0

GPIO[1]
Output Register

Value of this bit will be output to GPIO[1] pin if GPIO[1] is configured as an
output pin

Reset to 0

15 Reserved

RO Reserved

GPIO[2] Input

State of GPIO[2] pin

GPIO[2]
Output Enable

0: GPIO[2] is an input pin

1: GPIO[2] is an output pin

Reset to 0

PI7C8148A

2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

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Bit Function

Type

Description

GPIO[2]
Output Register

Value of this bit will be output to GPIO[2] pin if GPIO[2] is configured as an
output pin

Reset to 0

19 Reserved

RO Reserved

GPIO[3] Input

State of GPIO[3] pin

GPIO[3]
Output Enable

0: GPIO[3] is an input pin

1: GPIO[3] is an output pin

Reset to 0

GPIO[3]
Output Register

Value of this bit will be output to GPIO[3] pin if GPIO[3] is configured as an
output pin

Reset to 0

23 Reserved

RO Reserved

15.2.56 EEPROM CONTROL REGISTER OFFSET C8h

Bit Function

Type

Description

0 EEPROM

Start

Starts the EEPROM read or write cycle

During non-autoload periods, the bridge sets this bit to read/write data from/to the
EEPROM. This bit is kept asserted until the command has been delivered to the
EEPROM. Software must check to see if the Start bit becomes deasserted before
issuing the next command.

Reset to 0

EEPROM
Command

Sends the command to the EEPROM

0: EEPROM read

1: EEPROM write

Reset to 0

EEPROM Error
Status

1: EEPROM acknowledge was not received during the EEPROM cycle.

Reset to 0

EEPROM
Autoload
Success

0: EEPROM autoload was unsuccessful or is disabled

1: EEPROM autolad occurred successfully after RESET. Configuration registers
were loaded with values in the EEPROM.

Reset to 0

5:4

Reserved

Returns 00 when read. Reset to 00

7:6

EEPROM
Clock Rate

Determines the frequency of the EEPROM clock, which is derived from the
primary clock

00: Reserved
01: PCLK / 256 (33MHz PCI operation)
10: PCLK / 128
11: Reserved

Reset to 01

15.2.57 EEPROM ADDRESS REGISTER OFFSET C8h

Bit Function

Type

Description

15:8

EEPROM
Address

Contains the EEPROM address

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15.2.58 EEPROM DATA REGISTER OFFSET C8h

Bit Function

Type

Description

31:16 EEPROM

Data RW

Contains the data to be written to the EEPROM. After completion of a read
cycle, this register will contain the data from the EEPROM.

15.2.59 EEPROM TEST REGISTER OFFSET CCh

Bit Function

Type

Description

31:30

Reserved

Returns 00 when read. Reset to 00

EEPROM
MSB/LSB
Switch

Controls the order of the data bit stream

0: data bit stream in Most Significant Bit order (Test purposes only)

1: data bit stream in Least Significant Bit order

Reset to value of S_GNT#[2] pin during reset

EEPROM Fast
Autoload

Controls the autoload speed

0: Autoload in fast speed

1: Autoload in normal speed (Test purposes only)

Reset to value of S_GNT#[1] pin during reset

EEPROM
Autoload
Bypass Enable

Allows the EEPROM autoload to be bypassed

0: EEPROM autoload bypassed (Test purposes only)

1: EEPROM autoload not bypassed

Reset to value of S_GNT#[0] pin during reset

EEPROM
Autoload Status

EEPROM autoload status

0: EEPROM autoload was unsuccessful or is disabled

1: EEPROM autolad occurred successfully after RESET. Configuration registers
were loaded with values in the EEPROM.

Reset to 0

25 Reserved

RO Returns

when read. Reset to 0

EEPROM
Autoload
Disable

0: EEPROM autoload enabled

1: EEPROM autoload disabled

Reset to 1

15.2.60 SUBSYSTEM VENDOR ID REGISTER OFFSET F0h

Bit Function

Type

Description

15:0

Subsystem
Vendor ID

Returns 12d8h when read. Can be changed by EEPROM autoload

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2-PORT PCI-TO-PCI BRIDGE

ADVANCE INFORMATION

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JUNE 2004 Revision 1.04

15.2.61 SUBSYSTEM ID OFFSET F0h

Bit Function

Type

Description

31:16

Subsystem ID

Returns 8148h when read. Can be changed by EEPROM autoload.

16 ELECTRICAL AND TIMING SPECIFICATIONS

16.1 MAXIMUM RATINGS

(Above which the useful life may be impaired. For user guidelines not tested).

Storage Temperature

-65

°C to 150°C

Ambient Temperature with Power Applied

°C to 85°C

Supply Voltage to Ground Potentials (AV

and V

only]

-0.3V to 3.6V

Voltage at Input Pins

-0.5V to 5.5V

Note:
Stresses greater than those listed under MAXIMUM RATINGS may cause permanent damage to the
device. This is a stress rating only and functional operation of the device at these or any conditions
above those indicated in the operational sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.

16.2 DC SPECIFICATIONS

Symbol Parameter

Condition

Min.

Max.

Units Notes

Supply Voltage

3.6

Input HIGH Voltage

0.5 V

+ 0.5

3, 4

Input LOW Voltage

-0.5

0.3 V

V 3,

CMOS Input HIGH Voltage

0.7 V

+ 0.5

1, 4

CMOS Input LOW Voltage

-0.5

0.3 V

V 1,

ipu

Input Pull-up Voltage

0.7 V

V 3

Input Leakage Current

0 < V

< V

±10

µA

Output

HIGH

Voltage I

out

= -500

µA

0.9V

Output LOW Voltage

out

= 1500

µA

0.1

CMOS Output HIGH Voltage

out

= -500

µA

0.5

CMOS Output LOW Voltage

out

= 1500

µA

0.5

Input Pin Capacitance

CLK

CLK Pin Capacitance

IDSEL

IDSEL Pin Capacitance

Inductance

20 nH

Notes:
1. CMOS Input pins: SCAN_EN, SCAN_TM#

2. PCI pins: P_AD[31:0], P_CBE[3:0], P_PAR, P_FRAME#, P_IRDY#, P_TRDY#, P_DEVSEL#,
P_STOP#, P_LOCK#, P_IDSEL, P_PERR#, P_SERR#, P_REQ#, P_GNT#, P_RST, S_AD[31:0],
S_CBE[3:0], S_PAR, S_FRAME#, S_IRDY#, S_TRDY#, S_DEVSEL#, S_STOP#, S_LOCK#,
S_PERR#, S_SERR#, S_REQ#[3:0], S_GNT#[3:0], S_RST#, LOO, ENUM#.

3. V

is in reference to the V

of the input device.

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