Using High Resolution Oscillator for zephyr timer

RE: Using High Resolution Oscillator for zephyr timer

Gregoire_ — Wed, 26 Jun 2024 14:12:28 GMT

Good Afternoon, thanks for your response.

For our project we would need to generate a pulse of around 8/10us every time a specific condition is true in our code, so several pulses. (but there would be at least 1ms between each pulse generation due to our thread scheduling)

Best regards,

Gregoire

RE: Using High Resolution Oscillator for zephyr timer

Amanda Hsieh — Wed, 26 Jun 2024 14:06:29 GMT

This would need to use GPIOTE+TIMER+PPI, do you need only 1 pulse or several?

RE: Using High Resolution Oscillator for zephyr timer

Gregoire_ — Wed, 26 Jun 2024 09:45:59 GMT

Good Morning,

Thanks again for the help. I have tested the exemple code using nrfx timers. It work great and I am able to generate delays of the order of 10 us. Our problem is that when it comes to toggling a pin using those nrfx timer in a bigger application , the duration are not right.

Is there a simple way in zephyr to just generate standalone very short impulse on a gpio, in the order of 10us ?

In the case we would want to even shorter impulse (like 2/3 us) , is it also possible or are there some harware or processing time limitation that make that impossible ?

Best regards,

Gregoire

RE: Using High Resolution Oscillator for zephyr timer

Amanda Hsieh — Mon, 24 Jun 2024 13:52:12 GMT

Hi,

This post might help.

-Amanda H.

RE: Using High Resolution Oscillator for zephyr timer

Gregoire_ — Mon, 24 Jun 2024 08:18:52 GMT

Good Morning,

Thanks for your response. Enabling the HFXO with the clock subsys seems to work. However, even with the HFXO enabled, I am not able to generate timer durations under 100 µs.

For example, when using a periodic timer of 50 µs with k_timer_start(&my_status_timer, K_USEC(0), K_USEC(50));, the duration of 50 µs is not observed (we monitor a pin toggle with an oscilloscope to test this). We always have a minimum duration of around 120 µs.

I know that the Zephyr documentation states:

"Note that the timer’s duration and period parameters specify minimum delays that will elapse. Because of internal system timer precision (and potentially runtime interactions like interrupt delay) it is possible that more time may have passed as measured by reads from the relevant system time APIs. But at least this much time is guaranteed to have elapsed."

Does this mean that we can't generate delays smaller than 100 µs using Zephyr timers?

How should we proceed if we want to generate very short duration timers (in the order of 10 µs)?

Thanks for your help.

Gregoire

RE: Using High Resolution Oscillator for zephyr timer

Amanda Hsieh — Fri, 21 Jun 2024 14:36:12 GMT

Hi,

If you want to start the HFCLK, the simplest form is NRF_CLOCK->TASKS_HFCLKSTART=1;, then wait and clear the EVENTS_HFCLKSTARTED event. , but I would suggest to use the clock subsys. See this post to on how to enable HFXO as the timer.

Regards,
Amanda H.