Re: C64 MMU POC

From: Spiro Trikaliotis <ml-cbmhackers_at_trikaliotis.net>
Date: Thu, 11 Jul 2019 21:04:48 +0200
Message-ID: <20190711190448.4bce3iepm2c2rrco_at_hermes.local.trikaliotis.net>
Hello,

* On Thu, Jul 11, 2019 at 03:51:08PM +0200 Mia Magnusson wrote:
 
> Btw, another (albeit a bit strange) solution would be to have a state
> machine that only detects if the CPU has crashed, and if so enables the
> MMU registers and does a reset.

How many cycles does a RESET take? IIRC 8 cycles. Then, some
instructions would need to determine that it was a RESET on purpose, and
then, restarting where you left of, taking even more cycles.

One could give the 6502 a JMP instruction after a RESET, ignoring the
address lines, but this is not completely trivial, either.

Overall, this sounds rather expensive to me, so one would try to
circumvent changing the MMU. It's similar like on the 286er era PCs,
where you could leave the protected mode only by giving a RESET.

Regards,
Spiro.

-- 
Spiro R. Trikaliotis
http://www.trikaliotis.net/
Received on 2020-05-29 22:24:51

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