wfjm.w11/doc/simh_diff_mmu_nxm_prio.md

Known differences between SimH, 11/70, and w11a

SimH: MMU aborts have priority over NXM aborts

Let's assume a case where two address errors are present:

• the MMU rejects the access
• the MMU translated physical address is located in non-existent memory

In the KB11-C processor, the NXM condition is handled before the MMU condition. This leads to the surprising situation that the access is aborted with a vector 4 flow rather than a vector 250 flow.

SimH verifies the MMU abort condition first. xxdp program ekbee1 test 122 verifies the 11/70 behavior and is modified (see patch).

w11 also doesn't support this behavior, this is documented as w11 known difference.

Tested with SimH V3.12-3.