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From: The Natural Philosopher <tnp@invalid.invalid>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: Need help with PI PICO...
Date: Thu, 28 Mar 2024 11:56:14 +0000
Organization: A little, after lunch
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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;
>          }
> 
> 
>        }
> 

-- 
“It is hard to imagine a more stupid decision or more dangerous way of 
making decisions than by putting those decisions in the hands of people 
who pay no price for being wrong.”

Thomas Sowell