Tamas Rudnai wrote:
> On Sat, Jul 11, 2009 at 12:17 PM, Heinz Czychun <hczychun@lks.net> wrote:
> 
>>        Yes, sorry poor wording. Timer 0 is running, but when I
>> reprogram the PIC
>> with Timer 1 enabled (both running and interrupting), Timer 0 also
>> starts interrupting
>> even with the INTCON,T0IE bit cleared.
>>
> 
> Hi Heinz,
> 
> You do not have the T0IE enabled, but you still check the T0IF in your ISR
> routine. T0IF is independent from interrupt, it only tells if the Timer0 was
> overflowed or not. What happens is that you get an interrupt from Timer1,
> but then the ISR routine realizes that the Timer0 had an overflow as well
> therefore you treat the interrupt as it was generated by the Timer0.
> 
> Tamas

A classic example where you had *one* interrupt running
just OK and then, when adding a second interrupt source,
didn't add tests on xxIE-flags to the ISR... :-)

So test the xxIE flag *first* then test the xxIF flag.
If one xxIE flag is cleared, just jump to the next source.

That is :

  is T0IE set ? (interrupt enabled for TMR0)
  if no, goto test_tmr1
  if yes, check TOIF and run TMR0 ISR if set.

test_tmr1:
  is T1IE set ? (interrupt enabled for TMR1)
  if no, finish ISR (or goto next source/xxIE flag)
  if yes, check T1IF and run TMR1 ISR if set.

And so on for any number of interrupt sources.

Jan-Erik.



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