Re: Speeding up the 9100...

The way to make 68K stuff go fast is with a much higher 'local' CPU clock
and then cache RAM. Depending on the 9100 architecture (and where the
bottle neck is) you might be able to get away some tricks if it's executing
from a particular memory that's known to be quicker than 'necessary'.

IIRC, one of the old Atari/Amiga tricks was to look at a couple of the 68K
signals and basically switch in a couple of quicker clock cycles (like if
it's natively ~14MHz, you might sneak it a couple @ ~28MHz when it's just
doing 'internal' cycles and not out on memory. Again, IIRC, you want to use
the 68HC000 instead because they were *very* happy being overclocked in
general.

Our Amiga acceleratorr (the SupraTurbo 28) actually ran a 16MHz 'HC000 at
40MHz pretty reliably and 36MHz 'almost always'. We ended up backing it off
to 28MHz for production just because that was 2x Amiga 500/2000 speeds and
was totally safe. The key was to have some local 'fast' RAM (SRAMs) and
some cache tag RAM (IDT7174? That's from memory-- could be wrong). When an
address came along and the value wasn't in cache it'd be stored in the fast
local SRAM and the cache tag set, then next time if that same address was a
'match' on the tag RAM you knew you could substitute in the fast (28MHz)
clock for at least as long as it takes to fetch and deal with the cached
values.

So doing that you could cache things like ROM space (slowest), RAM
(slowish), but not I/O. Overall it did make a pretty big difference on
compute intensive stuff.

Something like a 68020 would help a little too since it has sort-of a
mini-cache built in (like three long words?) so it'll speed up loops and the
like, and there *may* be fewer clock cycles on some instructions vs. the
68000/010 too.

-Clay

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Received on Tue Jul 2 20:14:41 2013