Added basic 'torture'; turns up a timer, hits 100 times a sec, and shows some flicker on display :/
okay, interupt itself is okay; if gpio reads/writes are during vblank is okay; but if int goes off and read gpio, during non-vblank, it'll turd a bit. if interupt occurs and set volatile, and then answer volatile in vblank, we'd be fine; but can we wait up to 1/60th of a second to pick up the data .... that could kill z80 performance.