out-of-mainstream minis

Mouse mouse at Rodents-Montreal.ORG
Sat Jul 4 11:33:05 CDT 2015

> The problems revolve around the fact that instructions cannot be
> properly restarted on the 68000.  Not enough context is saved.
> [...]
> (The tricks done by those who did fix this consists of having a
> second processor which gets interrupted when you get a page fault,
> and the second processor do all the work related to the page fault,
> while the primary processor just stalls until the memory is
> available, at which point it can continue. There is no limits to how
> long the CPU can wait for memory to return data on a read.)

I recall hearing of a company that build a machine with two 68000s, one
running one instruction behind the other.  When the leading processor
got a page fault, hardware interrupted the lagging processor (which had
not yet encountered the faulting instruction) and there's a dance where
the two processors switch roles, allowing useful page faults.

Perhaps such a thing existed.  Perhaps my informant was misled - it
sounds like a plausible corruption of what you describe.  Perhaps my
own memory has bitrotted.  But it sounds to me as though it certainly
_could_ work.

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