[Simh] UNS: RE: FKABD0 diagnostics 11/34 fail in simh?

[Al Kossow]

Brad Parker wrote:

> In my case, I'm doing lock-step co-simulation with simh.  The rtl runs a 
> cycle and then simh runs a cycle and
> the results are compared.  Since simh doesn't pass the diags, my co-sim 
> fails.  I'm left wondering if I should
> fix simh to match the diag.  I've decided the answer is yes in my case.  
> Others might have  different take
> because they have different goals.
> 

Documenting the exact behavior is a goal of SIMH, as I understand it, so
I see no reason why Bob wouldn't accept the changes.

An accurate document describing implementation differences would be a good thing.

> I don't think the 11/70 guy was running co-simulation.  I think he was 
> just trying to pass diagnostics.
> But the result is the same - the diag failed and he was left wondering 
> what the correct behavior should
> be.
> 

Correct behavior is what the real hardware did. Of course, ECOs might change
that. Only way to be sure is to write test cases and run it on real hardware.
We ran into a few of those when the 68040 simulator was being written for the
PowerPC Macs.

Co-simulation with SIMH would not have been possible, since Bob didn't
implement all of the features of the 45 or 70. I suspect the 11/73 will
be the closest to reality, since he wrote the microcode for that implementation.