MVME5100 Single Board Computer Programmer's Reference Guide

2
Hawk PCI Host Bridge & Multi-Processor Interrupt Controller
AACK_ and TA_ allows the PPC Slave to assert a retry to the processor in
the event that the transaction is unable to complete on the PCI side. It
should be noted that any transaction that crosses a PCI word boundary
could be disrupted after only having a portion of the data transferred.
The PPC Slave cannot perform compelled burst write transactions. The
PPC bus protocol mandates that the qualified retry window must occur no
later than the assertion of the first TA_ of a burst transaction. If the PHB
was to attempt a compelled linkage for all beats within a burst write, there
is a possibility that the transaction could be interrupted. The interruption
would occur at a time past the latest qualified retry window and the PPC
Slave would be unable to retry the transaction. Therefore, all burst write
transactions are posted regardless of the write posting attribute within the
associated map decoder register.
If the PPC Slave is servicing a posted write transaction and the PPC FIFO
can accept the transaction, the assertion of AACK_ and TA_ occurs as soon
as the PPC Slave decode logic settles out and the PPC bus protocol allows
for the assertion. If the PPC FIFO is full, the PPC Slave holds the processor
with wait states (AACK_ will not be asserted) until there is room within the
PPC FIFO to store the pending transaction.
The PPC Slave divides PPC command types into three categories: address
only, write, and read. If a command type is an address only and the address
presented at the time of the command is a valid PHB address, the PPC
slave will respond immediately by asserting AACK_. The PHB will not
respond to address only cycles where the address presented is not a PHB
address. The response of the PPC Slave to command types is listed in
Table 2-1.
Table 2-1. PPC Slave Response Command Types
PPC Transfer Type
Transfer
Encoding
Transaction
Clean Block 00000 Addr Only
Flush Block 00100 Addr Only
SYNC 01000 Addr Only
Kill Block 01100 Addr Only
EIEIO 10000 Addr Only
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