I've been writing a lot of 8-bit assembler for the 6303, which is in the same processor family as the CPU in the TRS-80, which the author is writing code for (f

I've been writing a lot of 8-bit assembler for the 6303, which is in the same processor family as the CPU in the TRS-80, which the author is writing code for (for this project in case anyone is wondering: https://github.com/ajxs/yamaha_dx97 https://github.com/ajxs/yamaha_dx97). I ran into the exact same issue. I wrote a MAME driver for the target platform, so I could test my builds on my development machine. Obviously that sped things up a lot. The MAME debugger isn't built for unit testing, and it can't really be 'instrumented', but I was able to write a lot of scripts which could get me pretty close. You can set the debugger to initialise the system RAM from a file when it hits the breakpoint at the start of your function, then test the RAM against the desired output when it when it hits the breakpoint at the end. As clunky as this is, it saved me in a few tricky places!