Bug in Bob Supnik's Emulator?
Warren Toomey
wkt at henry.cs.adfa.oz.au
Fri Apr 3 11:00:34 AEST 1998
In article by Steven M. Schultz:
[re bugs in Bob Sunik's PDP emulator]
> My speculation is that there's a MMU emulation bug somewhere. 'vi' is
> a overlaid split I/D program. Overlays in 2.11BSD are done via
> 'page flipping' (altering MMU registers). Also 2.11 uses the 'expand
> downward' bit on the stack (as well as relying on MMR3 - i think that's
> the one - for instruction restart after growing the stack). If there's
> a subtle gotcha in the MMU emulation that will cause problems
> eventually. 2.11 is not alone in using the ED bit and instruction
> restart - if the problem is MMU related it could show up under other
> systems (V7). It would be interesting to know if 'vi' encountered
> problems on V7 but V7 doesn't have usermode overlays so getting 'vi'
> to run would be very problematic.
>
> Steven
The 2bsd distribution in the archive comes with an early non-overlayed vi
which compiles on V7. However, I haven't got it to work correctly yet. I
suspect that the /etc/termcap entry I was using is not recognised by this
early version of termlib.
This is all irrelevant to the emulator bug, BTW.
Steven, have you mentioned your hypothesis to Bob?
Warren
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