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- pdp11_sequencer.vhd: CPUERR cleared by CRESET - mminki.mac: added, procedure to initialize MMU, kernel I space only - test_w11a_cpuerr.tcl: added, test cpuerr register - added more README's - editorial changes
29 lines
1.1 KiB
Markdown
29 lines
1.1 KiB
Markdown
# ECO-028: `PS` init fix (2016-12-26)
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### Scope
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- Was in w11a from the very beginning
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- Affects: all w11a systems
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### Symptom summary
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The `PS` was at start-up and after CPU reset initialized to `000340`, thus
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`psw.pri = 7`, thus with interrupts disabled. The real 11/70 actually started
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with `000000` and `psw.pri = 0`, thus with interrupts enabled.
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### Background
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The `PS` reset behavior in the w11a was simply copied from the `simh`
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simulator in 2007, which at this time initialized the `PS` with `000340`.
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Only in 2013 (!) it was realized by Bob Supnik that this was incorrect.
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See the full story in the exhaustive commit message for
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[simh commit f0d41f1](https://github.com/simh/simh/commit/f0d41f15d792b9abc31e8530ee275453c7440a8c).
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### Fixes
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`PS` now initialized with `000000` to stay in line with the real 11/70 and simh.
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### Side effects
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Hopefully none. All `ibus` devices come up with interrupts disabled, so there
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shouldn't be any spurious interrupts at start-up.
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### Hindsights
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Even a very plausible behavior like _"disable all interrupts at power on"_ can
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be the incorrect one.
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