
Hawk PCI Host Bridge & Multi-Processor Interrupt Controller
MVME5100 Single Board Computer Programmer’s Reference (6806800H17B
)
86
2.3.3.4
PCI Master
The PCI Master, in conjunction with the capabilities of the PPC Slave, attempts to move data in
either single beat or four-beat (burst) transactions. The PCI Master supports 32-bit and 64-bit
transactions in the following manner:
All PPC60x single beat transactions, regardless of the byte count, are subdivided into one
or two 32-bit transfers, depending on the alignment and the size of the transaction. This
includes single beat 8-byte transactions.
All PPC60x burst transactions are transferred in 64-bit mode if the PCI bus has 64-bit mode
enabled. If at any time during the transaction the PCI target indicates it can not support
64-bit mode, the PCI Master continues to transfer the remaining data within that
transaction in 32-bit mode.
The PCI Master can support Critical Word First (CWF) burst transfers. The PCI Master divides
this transaction into two parts. The first part starts on the address presented with the CWF
transfer request and continues up to the end of the current cache line. The second transfer
starts at the beginning of the associated cache line and works its way up to (but not including)
the word addressed by the CWF request.
It should be noted that even though the PCI 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 2.1 Local Bus Specification requirements.
Table 2-9 PCI Master Command Codes
Entity Addressed
PPC
Transfer Type
TBST*
MEM
C/BE
PCI Command
PIACK
Read
x
x
0000
Interrupt Acknowledge
CONADD/CONDAT
Write
x
x
0001
Special Cycle
PPC Mapped PCI Space
Read
x
0
0010
I/O Read
Write
x
0
0011
I/O Write
Summary of Contents for MVME5100
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