KA630 guru?

From: Antonio Carlini <a.carlini_at_ntlworld.com>
Date: Thu Aug 5 17:37:10 2004

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.


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 Carlini arcarlini_at_iee.org
Received on Thu Aug 05 2004 - 17:37:10 BST

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