Memblers wrote:
Can you do address decoding for the IRQ vector, $FFFE and $FFFF, shutting the regular ROM off and putting something else in?
I think I can, I don't have a good understanding of how fast everything is. I was also sort of wondering if it could possibly be done without IRQs. Somehow if I could simply disable the ROM and get my hardware to feed the CPU "JSR $XXXX" that'd work just as well. I haven't thought about it too much but it seems it would screw up the game, at least the program counter no doubt.
Memblers wrote:
If the game is already in an interrupt, it won't work unless they enable IRQs inside the routine.
I see, I'll take that into account.
Memblers wrote:
I'm not sure what you mean by how fast can a register generate an IRQ. But the IRQ is level-sensitive and pretty quick. As soon as the current instruction finishes, it'll run the IRQ code if the /IRQ signal is low.
I should have worded it: If I write to a theoretical register which will hold /IRQ low (lets say with 0 latency), will it happen before the system starts on the next instruction? I would like my hardware to intercept a write and generate an IRQ before the next instruction to give me some serious control over the system one instruction at a time.