When using the PLB PIM with the MPMC, the Sl_MBusy signal is not asserted, even though the data has not been completely transferred to external memory. This can cause a port coherency issue when using EIEIO or Sync instructions to complete outstanding transactions before continuing instruction.
A manual workaround is to perform a read across the same port before continuing execution. This way the write will have completed across the memory, as all transactions across a particular port are in order.
This issue is planned to be resolved in the newest MPMC version in EDK 11.3.