[Simh] Software, firmware, and friends

[Johnny Billquist]

On 2017-03-12 22:51, Bob Supnik wrote:
> Well, I didn't have to ask for it, because I had it... ;) Without it,
> though, I could not have gotten the minute differences between the J-11
> and the other PDP-11s correct.

I know... :-)

> In general, I am no longer a fan of "approximate" simulations. If you
> just use the spec and ignore the implementation, then even if some
> particular test case (VMS Vxyz) works, the next piece of software may
> fail. I've seen this repeatedly - how the initial simulation of the RH
> worked with all DEC operating systems but failed with Unix, because a
> critical screw-up in the interrupt logic wasn't implemented faithfully;
> how the 750 simulation ran VMS but failed with BSD, because the UBA was
> a simple clone of the 780 (it's still wrong in critical aspects, as is
> the RH750); how the MicroVAX II & III/QVSS combo failed with Ultrix,
> because Ultrix cheerfully violates the SRM and the hardware just works.
> I'm still trying to work out the mischief that the SDS 940's tape drive
> perpetrates. The devil is in the details.

I seem to remember that I had to dig up some obscure documentation I had 
a long time ago when you were dealing with the RH70 in simh... :-)

You are, of course, correct in that without this intimate knowledge, the 
simulation will be a crapshoot.

> In the end, the implementer may choose to abstract the actual
> implementation away. But if he or she doesn't know what the
> implementation actually does - based on software, microcode, schematics,
> and so on - it's more or less a shot in the dark. One reason I never
> wrote additional VAX models, beyond the 780 and CVAX, is that microcode
> is not available for all the other 'big' VAXes (750, 730, 8200, 8600,
> 8900, 9000), and key specs, like bus adapters and device controllers,
> not to mention boot firmware, are missing for them as well as the 4000
> and 6000 series.

I think I might have everything you need for the 86x0, if you really 
want to. I also have a running machine around...
That said, emulating the hardware for that microcode will be some 
serious work. But I guess you might already know that too... :-)

Anyway - looking forward to the redesign of simh, as the current 
implementation is a horrible abstraction of hardware for the PDP-11... 
(Thinking about buses and controllers here...) :-)

	Johnny

>
> /Bob
>
> On 3/12/2017 12:00 PM, simh-request at trailing-edge.com wrote:
>
> From: Johnny Billquist<bqt at softjar.se>
>
>
>> Heck, the J11 also have firmware. I haven't seen anyone ask for that
>> yet. Instead people implement a PDP-11, and try to make it behave like
>> the J11.
>
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-- 
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