POKEY TIMER INTERRUPTS

[ac.tomo]

I have a bit of a dilemma. The program below sets and executes an IRQ Timer-1 interrupt but I'm baffled: The 'timer' interrupts are meant to be used when timing something quicker than jiffies (1/50thsec) right!? But that contradicts the fact that the timers are decremented every immediate V/Blank?

 

10 POKE 53768,0                                             - SET CLOCK FREQ.
20 FOR I=0 TO 9                                              - PUT M/C INTO P6
30 READ D:POKE 1536+I,D:NEXT I
40 DATA 173,10,210,41,248,141,24,208,104,64
50 POKE 528,0:POKE 529,6                               - SET ADDRESS OF TIMER-1
60 POKE 53760,30                                            - RE-EXECUTE DELAY (CLK PULSES)
70 POKE 16,193:POKE 53774,193                      - ENABLE INTERRUPT
80 POKE 53769,1                                              - RESET COUNTER

 

Am I doing something wrong, I'm confused. Please, can someone clarify this situation.

[Wrathchild]

You might be confusing software countdown timers (CDTMVx/CDTMAx) with pokey timer irqs (VTIMRx)?

[ac.tomo]

21 minutes ago, Wrathchild said:

You might be confusing software countdown timers (CDTMVx/CDTMAx) with pokey timer irqs (VTIMRx)?

Do you know, that is exactly what I was doing, thanks for that wrathchild. In all the years I've been programming I never realised that there were system software timers as well as the IRQ ones. That definately clears up that problem.

 

NB* Does anyone know if my code is correct, because I expect system control to return to Basic alike NMI DLI's in between IRQ executions but it doesn't, is this correct?

Edited June 22, 2021 by ac.tomo

[Rybags]

That code works.

For Pokey Timers much more frequent than that (looks to be every 8th scanline) you'd probably want to do a custom VIMIRQ handler.

The system IRQ handler puts the timers fairly low in the order of priority so there's a long code path before your code is run.

When doing that you'd then have to do extra stuff like testing and resetting IRQ status and enable bits.