
76
PRELIMINARY
82454KX/GX (PB)
A
3.8
Host to PCI Bus Command Translation
If a valid Pentium Pro processor bus command is directed at the bridge, the PB generates a PCI bus request.
When the PB is granted the PCI bus, it issues a PCI command after the commit point of the Pentium Pro
processor bus transaction. Pentium Pro processor bus commands that are directed at the PB and conse-
quently to the PCI bus must be converted into appropriate PCI bus commands. The PB is a non-caching agent
on the host bus; however, it must respond appropriately to Pentium Pro processor commands that are cache
oriented.
Table 11. Host to PCI Bus Command Translation
Host Bus Command
(ASZ = 36, DSZ=64)
Other Encoded Information
PCI Bus Command
Deferred Reply
don’t care
none
INTA
LEN: <= 8 bytes
Interrupt Acknowledge with BE[0] asserted.
Special Cycles
BE: Shutdown
none
BE: Stop Clock Acknowledge
PCI Special Cycle - Stop Clock Grant
BE: all others
none
I/O Read
LEN: <= 8 bytes
up to 4 BEs asserted
I/O Read (one or two transactions)
Branch Trace
Message
none
I/O Write
LEN: <= 8 bytes
up to 4 BEs asserted
I/O Write (one or two transactions)
Read Invalidate
don’t care
Memory Read Line (8 Dword burst starting
with the low address)
Code Read
LEN: <= 8 bytes without all byte
enables asserted
Memory Read (one or two transactions)
LEN: <= 8 bytes with all byte
enables asserted
Memory Read (2 Dword burst starting with the
low address)
LEN: 16 bytes
Memory Read (4 Dword burst starting with the
low address)
LEN: 32 bytes
Memory Read Line (8 Dword burst starting
with the low address)
Memory Read
LEN: <= 8 bytes without all byte
enables asserted
Memory Read (one or two transactions)
LEN: <= 8 bytes with all byte
enables asserted
Memory Read (2 Dword burst starting with the
low address)
LEN: 16 bytes
Memory Read (4 Dword burst starting with the
low address)
LEN: 32 bytes
Memory Read Line (8 Dword burst starting
with the low address)