
PRELIMINARY
77
A
82454KX/GX (PB)
3.9
PCI to Host Bus Command Translation
When a PCI bus command is directed at the bridge, the PB generates a BPRI# request or arbitrates for BPRI#
ownership if there are two bridges. The actual point in time when the BPRI# is issued depends on a number of
factors including whether the bridge accepted the PCI request or forced a retry to the PCI master, and when a
complete cache line is filled during a write command.
PCI bus commands that are directed at the PB and consequently to the host bus are converted into the
following appropriate host bus commands.
Central Agent
Reserved Transac-
tions with no data.
None
Reserved Encodings
These encodings are ignored. A bus time-out will complete the cycle
Memory Write
LEN: <= 8 bytes without all byte
enables asserted
Memory Write (one or two transactions)
LEN: <= 8 bytes with all byte
enables asserted
Memory Write (2 Dword burst starting with the
low address)
LEN: 16 bytes
Memory Write (4 Dword burst starting with the
low address)
LEN: 32 bytes
Memory Write and Invalidate or Memory Write
(8 Dword burst starting with the low address)
Table 12. PCI to Host Bus Command Translation
PCI Bus Command
Host Bus command
Memory Read
LEN:
≤ 8 or
LEN: 32 (When
CPU Line Read for PCI memory Read
Commands [Bit 8] is enabled in the PCI Read/Write Control
Register: 54-55h)
Memory Read Line
Memory Read
LEN:
≤ 8 or
LEN: 32 (When
CPU Line Reads for PCI Memory Read Line
Commands [Bit 3] is enabled in the PCI Read/Write Control
Register: 54-55h)
Memory Read Multiple
Memory Read
LEN:
≤ 8 or
LEN: 32 (When
CPU Line Read Multiple for PCI Memory Read
Multiple Commands [Bit 5] is enabled in the PCI Read/Write
Control Register: 54-55h)
Table 11. Host to PCI Bus Command Translation (Continued)
Host Bus Command
(ASZ = 36, DSZ=64)
Other Encoded Information
PCI Bus Command