Re: C64 MMU POC

Am 10. Juli 2019 17:51:00 schrieb laughton_at_cyg.net
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> Interesting...  So, you'd read several bytes whose value you actually
> don't care about...  but the decoder hardware would recognize *which*
> bytes you'd read; and, from that, infer what MMU operation you wanted?

Yeah. I used this technique to implement IO ports on the Atari ST ROM port :-)

Just used a 256 byte address range and used the lower 8 address bits as
output value when an address in that block was read

This way my Atari ST became an IEEE488 connected harddisk for my C64 :-)

André

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> cheers
> J
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>> and think about very unlikely
>> read sequences that won't be triggered by random register accesses.
>> Of course, with this method, such a register can't be read by the cpu.
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>> Frank