1023 B
Known differences between SimH, 11/70, and w11a
SimH: SPL doesn't have 11/70 behavior
On an 11/70, the SPL instruction in the 11/70 always fetches the next
instruction regardless of current mode, pending device, or even console
interrupts. This behavior is used in some xxdp diagnostic codes to prepare
a situation suitable for interrupt response testing.
SimH does not implement this behavior, SPL behaves like all other
instructions, and interrupts or traps are honored after it completes.
xxdp program ekbbf0 test 032 depends on the 11/70 behavior and is skipped
(see patch).
The w11 implements 11/70 behavior for SPL in kernel mode only. In supervisor
or user mode SPL is a nop and honors traps and interrupts, see
SPL on w11.
Several tcodes utilize the SPL behavior and
are skipped when executed on SimH
(see cpu_basics.mac test F2.3).
Tested with SimH V3.12-3.