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21 lines
938 B
Markdown
21 lines
938 B
Markdown
## Known differences between SimH, 11/70, and w11a
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### SimH: traced `WAIT` has J11 behavior
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On an 11/70 (and an 11/45) a traced `WAIT` will wait until an interrupt happens
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and finish without raising a trace trap because the interrupt has higher
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service precedence. The trace trap related to the `WAIT` will happen when the
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interrupt driver exits with an `RTI`.
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See also [trap and interrupt service order](simh_diff_service-order.md).
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On a J11 and other PDP-11 models, a traced `WAIT` falls through and raises a
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trace trap immediately. This is consistent with trace traps having higher
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precedence in those models.
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SimH uses the J11 service order with interrupts having the lowest priority for
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all PDP-11 models, and consequently, a traced `WAIT` falls through and raises
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a trace trap immediately.
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xxdp `ekbbf0` test 63 verifies the 11/70 behavior and is skipped.
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The w11 implements the proper 11/70 service order and `WAIT` behavior.
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