On an 11/70 (and an 11/45), a traced WAIT will wait until an interrupt happens
and finish without raising a trace trap because the interrupt has higher
service precedence. The trace trap related to the WAIT will happen when the
interrupt driver exits with an RTI.
See also trap and interrupt service order.
On a J11 and other PDP-11 models, a traced WAIT falls through and raises a
trace trap immediately. This is consistent with trace traps having higher
precedence in those models.
SimH uses the J11 service order with interrupts having the lowest priority for
all PDP-11 models, and consequently, a traced WAIT falls through and raises
a trace trap immediately.
xxdp program ekbbf0 test 063 verifies the 11/70 behavior and is skipped
(see patch).
The w11 implements the 11/70 service order and WAIT behavior.
This is verified in a tcode, the WAIT test is
skipped when executed on SimH
(see cpu_details.mac test A4.4 part 4).
Tested with SimH V3.12-3.