Oh, one minor point: I am not sure now by heart, but as far as I remember, there is something you need to do to make DMA continued after the interruption. It can be useful, but also problematic sometimes: the main program needs to aware to check if interruption happened and made it continue, you can't make the interrupt handler to do it, as then CPU won't return from the interrupt: another interrupt occurs -> soon, stack is overflowed badly. Surely, you can modify the stack to have different return address with RTI with also saving the original return address, or similar. Or implement some logic, to give the ability (which is maybe optional!) that DMA automatically continues after an RTI opcode is already executed. I'm not sure what C65 designers thought, or how it was intended to work. Not even speaking about the fact that maybe the INT bit was never working (though, as you pointed out as well, it does not mean that it cannot be implemented in M65 at some point, if system resource (FPGA) and human resources (VHDL coders) and the willpower (I am not sure if everybody finds this a useful and needs to be implementing feature) for it is all there :).