[chbot] Synco's !!!Choc fish challenge!!!!(Pulse length measurement)

[jimmy allen]

> I've had a frustrating day trying to code up a brushless DC motor
> controller... (hence the procrastinating).
> Anyway I'd like to put this winning chocolate fish up for grabs again to the
> first person that tells me how to measure a pulse-width (connected to an
> external interrupt), glitch-free!! :
> This is roughly what I got:
>
> #define TIMERWRAP     1024
>
> ISR(ExternalInterrupt)  // highest priority
> {
>     if (triggered on +ve edge) {
>        set to trigger on -ve edge;
>        count = TIMERWRAP - Timer;
>     }
>     else {
>         set to trigger on +ve edge;
>         count += Timer;
>         // Now Count should be the pulse length... but it has glitches see
> below
>     }
> }
>
> ISR(TimerOverflow)   // overflows at TIMERWRAP ticks
> {
>     count += TIMERWRAP;
>     ....
> }
>
> ISR(other)
> {
>    ...
> }
>
> Now the problem occurs (very infrequent) when both the TimerOverflow and
> External interrupt occur while another (non-nesting) ISR is being processed.
> The Ext Interrupt will be processed first therefore missing out on the
> extra TIMERWRAP. I've tried compensating by reading the interrupt flag
> register when processing the external interrupt, it reduces the frequency of
> glitches but as-long as there is any time between reading the flags register
> and the timer I get glitches.
> Is this one of those impossible micro-processor problems?
>
>

Hi Cynco

Could this problem be solve using a timer in very much the same way
ADC is done using a timer.Also what processor is being used.

Jimmy