[Simh] Hardware fidelity in the VAX family simulators

[Johnny Billquist]

On 2015-07-09 02:16, Robert G. Schaffrath wrote:
>
>> On Jul 8, 2015, at 8:10 PM, Johnny Billquist <bqt at softjar.se> wrote:
>>
>> On 2015-07-09 01:57, Robert Armstrong wrote:
>>>> I haven't found microcode sources or listings for the 750, 730,
>>>> MicroVAX I, or 8600, for example.
>>>
>>>    FWIW, the 725/730 was somewhat unique in that the micro store was entirely RAM.  All of the microcode was loaded by the CFE at power on and none was in ROM.  Also, the 730 micro engine was based on industry standard 29xx family bit slice parts.  It was a little like the 11/60 in that it was easy, in theory at least, to write custom microcode.  I've heard that certain customized versions of the 730 microcode were produced for special needs, and that DEC even supported this with some development tools, but I've never seen any such thing in the wild.
>>>
>>>    So, if anyway if anybody does find the sources or development tools for the 730/725 microcode, I'd love to see a copy.
>>>
>>>    Back to Bob's topic, I do have a running 730 system that could be powered on more or less any time.  I'm willing to run tests if anybody needs to experiment with the behavior of real hardware.  It's even on HECnet, so I could make remote access available.
>>
>> The 86x0 machines also have the microcode in RAM. It's all loaded from the FE RL02 at start up. I have the documentation for all the microcode machines of the 86x0, but I don't have the actual microcode sources, nor the tools used to build the binaries.
>>
>> That said, I guess it should be doable to disassemble the existing microcode if one really wanted to.
>>
>> The 11/60 was an interesting machine in that DEC actually provided the tools for customers to write their own microcode.
>>
>> The 11/750 had RAM to store patches to the microcode, but the basic version of the microcode was in ROM.
>>
>> Where did the 11/725 and 11/730 load their microcode from. Surely not the TU58...
>
> You nailed it. That pathetically slow tape drive was used to load the microcode. I had an 11/730 at my first job 29 years ago and the wait to get the bootstrap was interminable!

That is horrible. Even thinking of being absolutely dependent on a TU58 
to even start the machine is bad. Not to mention slow...

Surprised as well, as they did it better on the 11/750 (I think), where 
you don't need the TU58 for normal operation, but you still had the 
ability to patch the microcode as needed.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol