When using the MPMC in a Spartan-3 design in a dual-rank design, the chipselect is asserted too late after a read when switching banks. This could cause an activate failure and data corruption. In simulation, a memory model error similar to the following would occur:
ERROR: Activate Failure. Bank 1 must be Precharged.
This issue is planned to be fixed starting in MPMC v4.03.a and later, to be released in EDK 10.1, Service Pack 3.