Bug-for-bug compatibility [was RE: SimH DECtape vs. Tops-10 [was RE: Writing emulators [Was: Re: VCF PNW 2018: Pictures!]]]

Rich Alderson RichA at livingcomputers.org
Wed Feb 28 13:35:18 CST 2018

From: Doug Ingraham
Sent: Wednesday, February 28, 2018 9:53 AM

> This is a great story!  And it probably indicates that when developing the
> Toad-1 this particular diagnostic was never run from an original DEC generated
> tape or the Toad-1 would have failed the diagnostic.  Alternatively assembling
> the diag on the restoration project would have yielded a working multiply.

As it happens, this diagnostic is KI-10 specific, so no recompilation of the
KL-10 diagnostics would have caught it.

In addition, because the XKL-1 CPU was supposed to be identical to the KL-10,
it needed to pass the diagnostics *as provided* for the KL-10.

> So is someone going to fix the multiply instruction in the 20+ year old Toad?
> <grin>

Actually, they tried, but because they had stopped using the Toad-1 several
years earlier (and donated all the remaining spare parts to the museum), they
had no way to test in-house, and limited cycles for developing a fix.  If we
ever need to recompile diagnostics for the KI-10 (or, mirabile dictu, a KA-10!)
we'll use a Toad-2.


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