30 Jun
2016
30 Jun
'16
11:27 p.m.
scj(a)yaccman.com wrote:
My memory was that the 68000 gave the 8086 a pretty
good run for its
money, but when Moto came out with a memory management chip it had some
severe flaws that made paging and fault recovery impossible, while the
equivalent features available on the 8086 line were tolerable. There were
some bizarre attempts to page with the 68000 (I remember one product that
had two 68000 chips, one of which was solely to sit on the shoulder of the
other and remember enough information to respond to faults!). By the time
Moto fixed it, the 8086 had taken the field...
The 68451 did exist early. We had a "ExorMax" development system with the MMU
that we used to develop our UNOS derivate "VBERTOS" before we had our own
hardware.
The design bug in the mc68000 was that the execption stack did not contain the
complete microcode state for things like "*p++" and thus was not restartable at
the same state.
The ideas using two 68000 did put the main CPU into halt (from wehre it could
be restarted) and did only run the exception handling code on the second CPU.
Jörg
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