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Virtualizing the 6502 on a 6502 with 6o6
Okay, promises, promises. Here's the first of my bucket list projects I'm completing which I've intermittently worked on for literally two d...
For mitigating dangerous instructions, in-circuit emulators did exist — the Eastern House Software "Trap65" comes to mind, which turned bogus opcodes into trappable BRK s — but they were very expensive and at the time weren't generally sophisticated enough to directly manipulate live bus lines in a complex fashion. Meanwhile, the KIMplement kernel handles emulating the RRIOTs (picking up the writes from the harness), drawing the LEDs, servicing the TTY, inserting NMIs for stops and the Single-Step Switch, and also trapping portions of the KIM-1 ROM monitor. The unaccelerated C64 using geoRAM takes about a minute to discover that it has 32768 bytes free (it's actually more but this ROM was built with a hard cap at $8000, so you can put things at $8000 through $c0ff) because it has to swap the window back and forth between the instructions it fetches and the RAM locations it reads, or you can just type 32768 to skip all that.
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