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   On 27/03/2024 11:59, David Higton wrote:   
   > In message    
   >            The Natural Philosopher  wrote:   
   >   
   >> I am slightly curious as to how  the PICO could miss what is a several   
   >> hundred microsecond wide pulse.   
   >   
   > AFAICS there are many pitfalls:   
   >   
   > 1) An interrupt can be being serviced, so the pulse is over before you   
   > get to see it.   
   >   
   > 2) If you're looking for a pulse, you should be looking edge triggered   
   > rather than level triggered, but even then you may not get to react to   
   > the edge immediately because of an interrupt being serviced, so you'd   
   > get an anomalous result.   
   >   
   > 3) You can look level triggered, but you need to turn off all interrupts   
   > to ensure you really are loking at it in real time.   
   >   
   > 4) I had a play with an ultrasonic ranger a couple of years or so ago.   
   > I couldn't understand why I wasn't getting any return pulses at all.   
   > I eventually realised that I was sending another start pulse before   
   > the current cycle had finished.   
   >   
   > Regardless, you need an escape from any and every potential infinite   
   > loop.  Whatever you're doing.   
   >   
   > If you can use a hardware timer in the chip, that's a much more reliable   
   > solution.   
   >   
   > David   
      
   Thanks David   
      
   All make sense.   
      
   I think the next stage is to provide an escape from the infinite loops,   
   that documents itself and see where its hanging.   
      
   If interrupts are buggering it up, I am not sure how using an interrupt   
   would not also be buffered up by an interrupt.   
      
   The LWIP stack is all interrupt driven and I am loath to mess around for   
   fear of breaking comms.   
      
   In the end the pragmatic answer  may be to simply abort a failed reading   
   and try again.   
      
      
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