The Sinclair QL Forum

Is there any equivalent of a break vector that I can hijack in QDOS? I can find no such animal in Pennell or Dickens. I'm after a way for an assembler program to jump to a restart location if a specific key is pressed. I'd rather not do a key row scan as that'd add a substantial overhead. The nearest thing I've been able to find is to test SV.ARBUF (last key pressed) for Esc (1B). That works but has the disadvantage, like a key row scan, of being a poll (and therefore limited to specific test positions) but it also smells like just the sort of thing that wouldn't be portable across all QL OSs. I already handle exceptions but can't see how they could be made to emulate a break vector and they'd just end up with a poll at a later stage; similarly with interrupt handling or polled linked lists.

Am I missing anything and, if not, is use of SV.ARBUF portable (as long as it's indexed via MT.INF)?

Alan

ajb wrote:is use of SV.ARBUF portable (as long as it's indexed via MT.INF)?

I've used this before myself with no problems, obviously it has to be an offset ($8A) from the base of the system variables. I have notes about it in my Pennel margins:

If the high byte is zero, then the low byte is the key code; unless ALT is pressed whereby the high byte is the key code and the low byte is 255.

I suspect this is still the case under SMSQ etc. EDIT: Tested with the following, it's still valid.

Cheers,
Norm.

Thanks Norm. That's useful extra (ALT) information.

Alan