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  • gloriouscowgloriouscow@oldbytes.space
    Oct 14, 2026, 4:15 AM

    I decoded a bit more of the group decode ROM.

    The last four bits are not status outputs, they are an instruction family selector.

    Some of these are useful - here's IO operations, at 1111, which was conspicuously missing before, so that's good.

    Seeing things like DAD is also good because that has special flag behavior. I was able to use these families to eliminate several of the hardcoded opcode checks in the code.

    A table illustrating several values of the 4-bit instruction family selector in the v20 group decode ROM.
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  • gloriouscowgloriouscow@oldbytes.space
    Oct 14, 2026, 4:25 AM

    I also started working on the Rust version of the code generator.

    I've decided to replace MartyPC's V20 with this first. MartyPC's 8088 is pretty damn good already, but its V20 is pretty inaccurate, cycle-wise, so this will be a decent improvement, and I don't have to worry about breaking Area 5150 since it doesn't run on a V20 anyway.

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