You haven't given enough information to know if there will be a problem.
Depending on when A does its invalidate it could miss the second update.
A will read the correct messages, but it needs to know when they have arrived. Without synchronization A could miss an update, just as Jim said.
Thanks for your replies. I should have mentioned that A polls the MPB sections where B and C write into.
Just to be sure: Assume that the following pseudo-code is executed, does A get 0xBEAF from B and 0xCAFE from C?
/* A polls; t = 0 */
A: memcpy(read_buffer_B, local_mpb, 2); memcpy(read_buffer_C, local_mpb + 0x2, 2);
/* B and C send their messages; t = 1 */
B: my_message = 0xBEAF; memcpy(remote_mpb_A, &my_message, 2);
C: my_message = 0xCAFE; memcpy(remote_mpb_A + 0x2, &my_message, 2);
/* A polls again; data transfer from B and C to local MPB of A is already complete */
A: memcpy(read_buffer_B, local_mpb, 2); memcpy(read_buffer_C, local_mpb + 0x2, 2);
Remarks: memcpy(destination, source, size), according CL1FLUSHMBs omitted
Have you considered the write combine buffer in your code?
If you don't write 32 contiguous and alligned bytes, the WCB may delay the writes as an optimization (it's an optimization if you assume a single core system, like the p54c PCs were).
