5 Aug
2004
5 Aug
'04
10:37 a.m.
I've fallen a little behind in my reading
so I forgot to follow this thread.
I now favour the "executing out of prefetch
buffer" theory, reinforced
by the following comment snippet someone sent me, supposedly
taken from
the source to MicroVAX console ROMs:
; To turn on MMGT and execute the following REI depends
on a "quirk"
; of the MicroVAX chip. Namely, if the MTPR and REI
instruction are
; both fetched as part of the same instruction
prefetch, then the
; REI will be executed regardless of the enabling of
mmgt. However,
OK. So it sounds like you have strong evidence for
a chip bug here. The chances of getting it confirmed
are slim :-) - there was a list of Waivers granted
to various VAX implementations, but seeing it was
on a need-to-know basis. If the console code has
such comments in, it's best to believe them.
I guess they let the bug pass both because it's
relatively harmless and would have been expensive
to fix once the chip had been finalised.
I'm nto sure where this "Manx" is; I did
some poking around
with google
and found nothing helpful.
http://vt100.net/manx
Type in 78032 and see what pops up.
Heh. I don't suppose the microcode is available
anywhere?
I don't have the KA630 microcode and I don't know anyone who
does. The group I worked with produced the DEMSA and DEMSB
which were both based on the 78032, so they must have had
example console code lying around. But I can guarantee
that's long gone (and was probably long gone before I
got there).
Antonio
--
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Antonio Carlini arcarlini(a)iee.org