[Simh] Which PDP-11 to choose

[Eric Smith]

On Mon, Jul 1, 2019 at 3:10 PM Seth J. Morabito <web at loomcom.com> wrote:

> An interesting question! It's true that none of the simulators currently
> do microcode simulation, but I don't see why they couldn't. Certain
> assumptions about clock calibration may be in question, but I'm not
> sure. Even if they were, I think it's a surmountable problem and not
> fundamentally impossible given SIMH's architecture.


I've done microcode level simulation of various systems including four
generations of HP calculators.

I've done some work toward microcode level simulation of the LSI-11,
Western Digital WD16, and Western Digital Pascal Microengine, all of which
use the same chipset with different microcode and macroinstruction decode
PLAs.  I got to the point where the Pascal Microengine can successfully
execute the first few p-code instructions of a boot ROM. (Note that the
most common versions of the WD Pascal Microengine don't actually have a
boot ROM.)

While I have dumped the microcode for the LSI-11, WD16, and multiple
microcode releases of the Pascal Microengine, I have only completed
transcription from photomicrographs of the PLAs of the Pascal Microengine.
The PLAs of the LSI-11 and WD16 still need to be transcribed.

A partially reverse-engineered disassembly of the LSI-11 microcode is in
this github repo:
    https://github.com/brouhaha/lsi11uc
Without the transcribed PLAs, it isn't complete or useful.

Best regards,
Eric
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