User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 8: PCI Bus and HyperTransport Fabric Page
233
any PCI access will be issued with a retry. Software on the part should do initial configuration of the map
registers and set the subsystem information before writing a zero to the rd_host bit and flush the write to the
interface by following it with a dummy read that will return UNPREDICTABLE data. To be compliant with the
PCI specification this must be done within 1 second (0.55 on a 66 MHz bus) of the PCI reset being deasserted.
While the system is running with the rd_host bit clear ZBbus writes may be done to the map entries and the
SignaINTA register. Writes to the SubSysSet register will result in the SubSystem ID being updated, but the
results of changing this after device enumeration is system specific: the subsystem information may never be
read again or the operating system may assert an error because static information changes. Reads to any of
the PCI configuration registers will return UNPREDICTABLE data. The rd_host bit may be set to give read
access to the map entries, SubSysSet and SignalINTA, but while the bit is set any read requests from the PCI
bus will be issued retries (read access will probably only be needed for debugging).
Table 131 summarizes access to the PCI configuration registers.
Table 126: PCI CSR Access Rules
Register
ZBbus Read
ZBbus Write
PCI Read
PCI Write
Host Mode
Device/Vendor ID (
0
)
Class/Revision (
8
)
Valid data
Ignored
Unpredictable
Unpredictable
Map Entries (
44-80
)
SubSysSet (
8C
)
SignalINTA (
90
)
Valid data
Write register
Unpredictable
Unpredictable
Interface revision 3 or later
VendorIdSet (
9C
)
ClassRevSet (
A0
)
Valid data
Write register
Unpredictable
Unpredictable
Others
Valid data
Write register
Unpredictable
Unpredictable
Device mode with rd_host = 1
Device/Vendor ID (
0
)
Class/Revision (
8
)
Valid data
Ignored
Retried
Unpredictable
Map Entries (
44-80
)
SubSysSet (
8C
)
SignalINTA (
90
)
Valid data
Write register
Retried
Ignored
Interface revision 3 or later
VendorIdSet (
9C
)
ClassRevSet (
A0
)
Valid data
Write register
Retried
Ignored
Others
Unpredictable
Unpredictable
Retried
Unpredictable
Device mode with rd_host = 0
Device/Vendor ID (
0
)
Class/Revision (
8
)
Unpredictable
Unpredictable
Valid data
Ignored
Map Entries (
44-80
)
SubSysSet (
8C
)
SignalINTA (
90
)
Unpredictable
Write register
Unpredictable
Unpredictable
Interface revision 3 or later
VendorIdSet (
9C
)
ClassRevSet (
A0
)
Unpredictable
Write register
Unpredictable
Unpredictable
Others
Unpredictable
Unpredictable
Valid data
Write register