2-18
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Raven PCI Host Bridge & Multi-Processor Interrupt Controller Chip
2
The PCI master can support Critical Word First (CWF) burst transfers. The
PCI master will divide this transaction into two parts. The first part will
start on the address presented with the CWF transfer request and continue
up to the end of the current cache line. The second transfer will start at the
beginning of the associated cache line and work its way up to (but not
including) the word addressed by the CWF request.
It should be noted that even though the master can support burst
transactions, a majority of the transaction types handled are single-beat
transfers. Typically PCI space is not configured as cacheable, therefore
burst transactions to PCI space would not naturally occur. It must be
supported since it is conceivable that bursting could happen. For example,
nothing prevents the processor from loading up a cache line with PCI write
data and manually flushing the cache line.
The following paragraphs identify some associations between the
operation of the PCI master and the PCI 2.0 Local Bus Specification
requirements.
Command Types:
The PCI Command Codes generated by the PCI master depend on the type
of transaction being performed on the MPC bus. Please refer to
for a further description of MPC bus read and MPC bus write.
summarizes the command types supported and how they are
generated.
Table 2-4. PCI Master Command Codes
Entity Addressed
MPC
Transfer Type
TBST*
MEM
C/BE
PCI Command
PIACK
Read
x
x
0000
Interrupt Acknowledge
CONADD/CONDAT
Write
x
x
0001
Special Cycle
MPC Mapped PCI Space
Read
x
0
0010
I/O Read
Write
x
0
0011
I/O Write
-- Unsupported --
0100
Reserved
-- Unsupported --
0101
Reserved
MPC Mapped PCI Space
Read
1
1
0110
Memory Read
Write
x
1
0111
Memory Write