Pci/Mpc Contention Handling - Motorola MVME2600 Series Reference Manual

Raven PCI Host Bridge & Multi-Processor Interrupt Controller Chip

PCI/MPC Contention Handling

2
2-20
The Raven has a stall detection mechanism that detects when there is a
possible resource contention problem (i.e. deadlock) as a result of
overlapping MPC and PCI initiated transactions. The MPC Slave and the
PCI Slave functions contain the logic needed to implement this feature.
The PCI Slave function contributes to the stall detection mechanism by
issuing a stall signal to the MPC Slave function whenever it is currently
processing a transaction that must have control of the MPC bus before the
transaction can be completed. The events that activate this signal are:
PCI read cycle
PCI non-posted write cycle
PCI posted write cycle with flush-before-read (FLBRD) enabled
PCI posted write cycle and internal FIFO full
The MPC Slave function determines its future actions based on the stall
signal and the current MPC bus activity. If the MPC Slave function
determines there will be contention between a cycle completing on the
MPC bus and an incoming PCI cycle, the MPC Slave will issue a retry for
the current MPC transaction. This retry will free up the MPC bus and allow
the PCI initiated transaction to complete. An idle MPC bus obviously gives
immediate access to the pending PCI initiated transaction.
If the MPC bus is currently supporting a read cycle of any type, the cycle
will be terminated with a retry. Note that if the read cycle is across a mod-
4 address boundary (i.e. from address 0x...02, 3 bytes), it is possible that a
portion of the read could have been completed before the stall condition
was detected. The previously read data will be discarded and the current
transaction will be retried.
If the MPC bus is currently supporting a posted write transaction, the
transaction will be allowed to complete since this type of transaction is
guaranteed completion. If the MPC bus is currently supporting a non-
posted write transaction, the transaction will be terminated with a retry.
Note that a mod-4 non-posted write transaction could be interrupted