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MiSTer-devel / CoCo2_MiSTer

CoCo2 / Dragon Core for MiSTer
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Hi speed POKE doesn't do anything #1

Open dshadoff opened 4 years ago

dshadoff commented 4 years ago

POKE 65495,0 would increase speed of the CoCo by either changing the CPU clock, or altering the pattern of refresh (I don't remember clearly). This would work when accessing part of memory, but not all (there was another one for the other part).

Need clearer details, and to implement.

dshadoff commented 4 years ago

Update: changes timing of SAM CPU clocks when accessing upper half of memory. See MC6883 datasheet

dshadoff commented 3 years ago

Timing state-change diagrams in 6883 code don't match those in the datasheet; updating them (slow mode) causes issues with the 6847 video display, although CPU still seems to work OK.

Making the necessary changes to state-changes in order to add double-speed (but based on the as-is, incorrect timings) causes instability.

This means that the 6847 needs a complete overhaul, and 6883 needs to have its timings corrected in order to set a new baseline before the modified timings can work. Hopefully the 6809 isn't also based on improper timings.

This will be a big job to correct.