Motorola MVME2300 Series - Manual (Page 78)

2-8 Computer Group Literature Center Web Site
Raven PCI Bridge ASIC
2
MPC Write Posting
The MPC write FIFO stores up to eight data beats in any combination of
single- and four-beat (burst) transactions. If write-posting is enabled,
Raven stores the data necessary to complete an MPC write transfer to the
PCI bus and immediately acknowledges the transaction on the MPC bus.
This frees the MPC bus from waiting for the potentially long PCI
arbitration and transfer. The MPC bus may be used for more useful work
while the Raven manages the completion of the write-posted transaction
on PCI.
All transactions will be completed on the PCI bus in the same order that
they are completed on the MPC bus. A read or a compelled write
transaction will force all previously issued write-posted transactions to be
flushed from the FIFO. All write-posted transfers will be completed before
a non-write-posted read or write is begun, to assure that all transfers are
completed in the order issued. All write-posted transfers will also be
completed before any access to the Raven’s registers is begun.
MPC Master
The MPC master will attempt to move data using burst transfers wherever
possible. A 64-bit-by-16 entry FIFO is used to hold data between the PCI
slave and the MPC master to ensure that optimum data throughput is
maintained. While the PCI slave is filling the FIFO with one cache line
worth of data, the MPC master can be moving another cache line worth
onto the MPC bus. This will allow the PCI slave to receive long block
transfers without stalling.
When programmed in “read ahead” mode (the RAEN bit in the PSATTx
register is set) and the PCI slave receives a Memory Read Line or Memory
Read Multiple command, the MPC master will fetch data in bursts and
store it in the FIFO. The contents of the FIFO will then be used to attempt
to satisfy the data requirements for the remainder of the PCI block
transaction. If the data requested is not in the FIFO, the MPC master will
read another cache line. The contents of the FIFO are “invalidated” at the
end of each PCI block transaction.