Re: [avr-gcc-list] efficient Timer Interrupts

[Keith Gudger]

First, why do you need to save the 2 to 4 cycles that using RAM (vs
registers) saves?  If your interrupt routine is taking too long, just set
a flag in your interrupt routine and do your external A/D processing in
your main loop.  This will save a whole lot more than just putting the
variables in registers.

If you still want to save these 2 cycles, look for some I/O location
you're not using, and use that to store your variable.  INs and OUTs take
only 1 cycle (like using registers).

On Wed, 22 Oct 2003, Torsten Hahn wrote:

> Hi,
> 
> i have an application where i want do stuff in an timer interrupt, but 
> i want do the stuff only n times. So a solution would be the following:
> 
> 
> volatile uint16_t cnt = 10000;
> 
> 
> SIGNAL(SIG_OUTPUT_COMPARE0)
> {
>       // do stuff, e.g.
>       // read data from an extern adc
>       // accumulate data ...
> 
>       if(cnt--) {
>               // stop the timer0 / interrupt and set an "ready" flag
>       }
> }
> 
> The problem for me is, that using an extern (ram) var as a counter 
> consumes much processor cycles (loading the var from ram, decrementing, 
> write back). Is there a better (faster) solution ? Iam looking for a 
> way to stop for example the timer 0 exactly after  a given number of 
> executions.
> 
> Any Ideas ?
> 
> thx,
> Torsten.
> 
> 
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