There is a group of Spectrum games that come with a Z80 snapshot of an assembler loaded with the tailored driver(see
this file), others not. The most important data is the memory position of the coordinates, max and min positions and fire buttons, but I think the rest of the K-mouse routine is practically the same.
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I like very much your solution, but there are some minor problems:
- EP128emu still doesn't emulates mouse, XEP128 does but I don't know if it manages snapshots.
- I have to study how can I patch code into a snapshot.... not a big problem, I only need some hints... There are some empty memory zones that can fit the routine.
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If at the end you will try to insert the modified code in SWAP, why don't you try to first extract the game plain executable for me?
I could then disassemble or hex-edit it to study, and try the modified code on the real machine. Once finished you can join the pieces again easier.