16 Jan
2001
16 Jan
'01
11:41 a.m.
Your knowlege of this is so far beyond mine I can barely follow. Even
that is too complimentary to describe the gap, but I'd rather not
discourage you by measuring the gap. In this I follow.
I was suggesting a software approach (virtual mmu), but the Atari XE has a
fairly capable mmu in that it allows multiple processors to access memory
separately without the intervention of the cpu. I think a combination of
custom software and this hardware would perform better than a solely
software approach would. I could well be wrong, but with my limited
knowlege it is hard for me to find a fault in the argument. LUnix is a new
word for me. Any more info? I could search for it, but you seem to know
your stuff and that is a rare thing I'm not likely to find in a blind
search.
Regards,
Jeff
In <200101162115.NAA11712(a)stockholm.ptloma.edu>du>, on 01/16/01
at 05:41 PM, Cameron Kaiser <spectre(a)stockholm.ptloma.edu> said:
> There are quite a number of multitasking 6502
machines out there.
> Homebrews and C64s are represented.
Yep, I've played with LUnix and OS/A65. Both fun
but not really Unix.
LUnix NG does have one cool feature; it can do PPP out of the box on a
stock C64.
> Can you make a 6502-based machine 'do'
virtual memory?
Not natively, which was why I wrote:
> at 03:31 PM, Cameron Kaiser
<spectre(a)stockholm.ptloma.edu> said:
>
> >I run AIX and NetBSD myself! :-) And, one of these days when I get my
> >6502-on-6502 virtual CPU implementation done, my C64 will run my own
> >Unixy flavour too (just to make this on-topic somewhat).
... a virtual CPU implementation. Actually, what it
would do is distill
instructions down to their absolute, immediate or implied addressing
counterparts (instead of zp-indexed, absolute indexed, indirect, etc.),
and then munge the address operands to point to the right memory block.
It would move stepwise through code like that, with things like branches
and stack manipulations being emulated operations. There is no good way,
short of one fancy piece of MMU logic, to do VM on the 6502 currently.
So, with the advent of fast CPUs for the C64 like the SCPU, why not do it
in software? :-) It would probably not run badly even on a stock system.
Ach, du lieber -- this thread is back on topic!
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