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c9d447f2be
- rtl/w11a - pdp11_sequencer.vhd: tbit logic overhaul 2, now fully 11/70 compatible - tools/tcode - cpu_details.mac: add A4.4 part 0,8,9,10 - cpu_mmu.mac: use m*pd
27 lines
1.1 KiB
Markdown
27 lines
1.1 KiB
Markdown
## Known differences between SimH, 11/70, and w11a
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### SimH: trap and interrupt service order has J11 behavior
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The 11/70 (and the 11/45) differ from all other PDP-11 models in the order in
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which interrupts and traps are honored after the successful completion of an
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instruction. On the 11/70, interrupts have precedence over T-bit trace traps,
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on all other models interrupts have the lowest priority.
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As consequence, `RTI` _can_ be used on an 11/70 to exit from an interrupt driver,
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and exactly one trace trap will happen when an interrupt is honored after
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a traced instruction. On all other models, `RTT` _can_ be used to exit from
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an interrupt driver to prevent a double trace trap, one before the interrupt
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and one after the hander exit.
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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.
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The w11 implements the 11/70 service order.
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This is verified in a [tcode](../tools/tcode/README.md), the test is
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modified when executed on SimH
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(see [cpu_details.mac](../tools/tcode/cpu_details.mac) test A4.4 part 3).
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See also [traced `WAIT`](simh_diff_traced-wait.md).
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Tested with SimH V3.12-3.
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