[deater]

you can also get a regular interrupt from a Mockingboard sound card, these days it's probably more likely people will have one of those (especially if they are running under emulation) than a mouse card.

when writing demos and games that have mockingboard support it's always tempting to take advantage of the timers on the 6522 chips on it, though it does mean that the programs wouldn't have been useful for most people back in the 80s/90s