anyway, check this out: a complete high performance ARM7TDMI debug probe* https://github.com/whitequark/glasgow/blob/applet.debug.arm.arm7tdmi/software/glasgow/applet/debug/arm/arm7/__init__.py
it took me 3 days or so and 180 lines of code to implement it. that's right, one hundred eighty
* not a debugger; a debugger presents a UI, a debug probe can merely execute code and read/write data