Re: Need help with PI PICO...

On 28/03/2024 08:35, Björn Lundin wrote:

On 2024-03-25 16:57, The Natural Philosopher wrote:

That is, some asynchrounous event in this sequence
>
     gpio_put(ULTRASONIC_OUT,1);
     sleep_us(10);
     gpio_put(ULTRASONIC_OUT,0); //reset the input
//if asynch event lasting more than 100uS occurs here...
     // wait for echo pulse start
     while(!gpio_get(ULTRASONIC_IN))
         ;
//then the low-high-low echo pulse will never be detected.

  if you change the wait body to include a counter then you could realize that when the counter had reached a high number - you missed the pulse.
Just try again then. Getting a reading is not that time sensitive - or?
 

That will be the next strategy.
I need to isolate exactly which bit is failing, and can remove all the other debug code.
If it turns out to be a one in a thousand issue  it probably isn't worth trying to avoid it, as you say, simply take another sample

:START
       int cnt = 0;
       gpio_put(ULTRASONIC_OUT,1);
       sleep_us(10);
       gpio_put(ULTRASONIC_OUT,0); //reset the input
  //if asynch event lasting more than 100uS occurs here...
       // wait for echo pulse start
       while(TRUE) {
          if (! gpio_get(ULTRASONIC_IN)) {
            cnt++
         } else {
           break;
         }
          if (cnt >= TOO_HIGH_VALUE) {
            goto START;
         }
         }
 

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