[Simh] Is it possible to simulate the first Vaxen I ever used?

[Jonathan Welch]

https://en.m.wikipedia.org/wiki/Microcode

On Mon, Mar 23, 2020, 5:49 PM Ray Jewhurst <raywjewhurst at gmail.com> wrote:

> Slightly off topic, could someone explain more about what microcode is and
> how it works? The fact that the CPU instructions are they themselves
> programmed in seems unfathomable.
>
> Ray
>
> On Mon, Mar 23, 2020, 5:33 PM Clem Cole <clemc at ccc.com> wrote:
>
>>
>>
>> On Mon, Mar 23, 2020 at 3:57 PM Johnny Billquist <bqt at softjar.se> wrote:
>>
>>> The VAX-11/750 used 2901 though...
>>>
>> 750 was made out of custom CMOS gate arrays.  The main adder was analyzed
>> as part of my thesis [long story - not for here, but a very clever
>> circuit.  I would later get to know the guy that did it].     Paul Gilbeau
>> and Dick Monroe were the main microcoders on the 750.  I'm pretty sure that
>> Paul was also one of the 780 microcode folks.   Very interesting guy. I
>> used to say he had a worm's eye view of the world -- perfect for his job as
>> lead microcoder; but trying to get up a level could be difficult.  I've
>> lost track of them both, although I still talk to Dave Cane a couple of
>> times a year and I think he knows how to find most of the HW team.
>>
>> I'm fairly sure that the 750 used te BLISS based Micro2 tools as Tim
>> suggested and as I said, we cloned them at Masscomp in C (which later it
>> went west). Tim, you tell me, I thought the Masscomp version got sent to
>> the Jupiter team, but I'm pretty sure it was used for Prism.  I remember us
>> getting a 'bug report' because VAX-11/C didn't like something BSD's yacc
>> had generated at one of the Hatfield/McCoy parties. I remember changing
>> what it was and email it the next day.
>>
>> FWIW:   All of the Masscomp FP/AP and the DACP used that set of
>> microcode tools since they were all AMD 29xx based.   IIRC, Chuck Palmer
>> overhauled the original hack we did for Paul and Dick because a few Masscomp
>> customers wanted to write custom DACP microcode and originally it was
>> not too easy.   I probably have a manual for that still around and maybe
>> even the tools. But, since I don't have a DACP on the MC500 I still
>> have,  I never bother scooping up the tools.
>>
>> Also, I know that there was an Intel 808x processor (85 I think) that
>> shipped in the 750, but it was not an FEP.  It was limited to running the
>> cartridge tape controller.  I don't remember how the console serial port
>> was done (the 780 it was part of the FEP).  The 750 microcode did the boot
>> as someone else pointed out.  I've forgotten how the microcode was loaded
>> on a cold start.   I thought there was something in a ROM/EPROM, but I've
>> forgotten.  I do know the cartridge tape unit was needed to update the
>> microcode and that was the only way to do it.  But I don't remember you
>> need to have the tape on a cold reboot the like floppies on a 780, but I
>> could have forgotten.
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