[Simh] Hardware fidelity in the VAX family simulators

[John Forecast]

On Jul 8, 2015, at 5:39 PM, Bob Supnik <bob at supnik.org> wrote:

> First, congratulations to Mark for running the current Ultrix 750 problem to earth.
> 
> Second, a brief diatribe about the need for fidelity to the hardware in the VAX simulators, which is (on the face of it) lacking outside the 3900 and 780 simulators.
> 
> I have preached and documented the need for reasonable fidelity to hardware in implementing simulators. The papers on the SImH web site are filled with examples of minute details gumming up software behavior if a simulator gets them wrong. It looks to me like the 750, 730, 8600 are cut-and-paste jobs on the 780, and the MicroVAX I and II on the 3900. I admit there are strong family resemblances and, in some cases, reuse of hardware (the 8600 uses some of the 780 IO adapters), but as Ultrix proved, running VMS is an insufficient proof of correctness. Without reading (and implementing) the gory details of all the system-specific hardware, something is going to break. And if the goal is just to run VMS, why bother with variant models? The 780 and 3900 between them cover the complete history of VAX/VMS, Ultrix, and all the BSD variants.
> 
> While the 750 now runs Ultrix, will it run the next OS it is given? Even with the current fix, there are multiple errors remaining in the UBA. The 730 won't boot Ultrix off the RB80; and so on.
> 
> So my challenge to the community is twofold. First, is there more documentation on the variants available somewhere? I haven't found microcode sources or listings for the 750, 730, MicroVAX I, or 8600, for example. Second, are people prepared to "adopt" a model, read its documentation, and clean it up?
> 
> End of diatribe.
> 
> /Bob

Let’s not forget different peripheral usage models between the various OSs. I have an open issue where Ultrix 2.0/2.2 run fine on a Microvax II, but as soon as I enable DECnet the system panics with:

	panic: qe: Non existent memory interrupt

Mark, were you able to reproduce this problem with the updated image I pointed you at?

  John.