Bug in Bob Supnik's Emulator!

[Greg Lehey]

On Thu,  2 April 1998 at 23:50:23 -0800, Steven M. Schultz wrote:
> Greg -
>
>> FWIW, I've used the latest (and not yet committed) version of the
>> Begemot emulator to run 2.11BSD for over a week.  In that time, I
>
> 	AH, a new and improved version?  Great!  SOmething to look forward to.

It's the one I've been using all along.  I never used an older version.

>> unexplained problems with the assembler, which Steven Schultz
>> considers to be due to the emulator (more specifically, instruction
>> restart), but Hartmut Brandt (the principal author) thinks this is unlikely.
>
> 	It was a possibility - the only other thing which I've seen cause
> 	similar problems was bad memory/cache.  I presumed your memory
> 	wasn't failing ;).

Reasonable assumption.

> 	Programs suddenly dying for no apparent reason on otherwise healthy
> 	"hardware" led me to suspect a problem with the emulator.  The final
> 	arbiter of course is a real PDP-11 :)

Sure, that makes sense.  I did too, but I couldn't see anything obvious.

> 	I take it then that the problems went away as mysteriously as they
> 	arrived and that all is well with your system (no more assembler
> 	or kernel recompile troubles)?

Well, not quite.  I finally got back to the real work I should have
been doing, and I haven't had time to look at it again since.  But
they went into hiding when I tried to show them to Hartmut :-) I think
we still have a problem somewhere.  BTW, Hartmut had already upgraded
to PL 40? before I tried to start, so I'm still not completely
convinced that it's not something I did wrong in upgrading.

> 	Not having any great need of an emulated PDP-11 I've not pursued
> 	the (suspected) bug in Bob Supnik's emulator.  Even on a PentiumPro
> 	an emulated 11 is slower than a real 11/73 (and a lot slower than an
> 	11/93 - which I should cease neglecting and stuff a SCSI card into
> 	some day as I did with the 11/73).

Interesting.  I was running this on an AMD K6/233, which should be
slower than a PPro, and I had the impression it was faster.  Does
anybody have some benchmarks?

Greg

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