PWM output with stable frequency

RE: PWM output with stable frequency

takashina hiroki — Wed, 09 Oct 2019 23:36:41 GMT

>> For PWM in pwm_library / pwm_driver, it's the HFCLK that decides how stable the frequency is.
>> The low_power_pwm library uses the app_timer (which in turn use RTC1 (uses LFCLK)). But the toggling is done in interrupt context, so other interrupts could affect the PWM timing.

From the above, I recognize that there is no way to achieve stable PWM output with PWM with LFCLK (XTAL) as the clock source.
Is my perception correct?

RE: PWM output with stable frequency

Sigurd — Wed, 09 Oct 2019 10:12:49 GMT

The low_power_pwm library uses the app_timer (which in turn use RTC1(uses LFCLK)). But the toggling is done in interrupt context, so other interrupts could affect the PWM timing. If you want to avoid that, use e.g. pwm_library instead.

RE: PWM output with stable frequency

takashina hiroki — Mon, 07 Oct 2019 23:26:55 GMT

>> For PWM in pwm_library / pwm_driver, it's the HFCLK that decides how stable the frequency is.

I want to select LFCLK (XTAL) as the PWM clock source.
Therefore, these cannot be used.
Is there a way to perform stable PWM output with a PWM whose clock source is LFCLK (XTAL)?

RE: PWM output with stable frequency

Sigurd — Mon, 07 Oct 2019 09:33:08 GMT

[quote userid="72172" url="~/f/nordic-q-a/52893/pwm-output-with-stable-frequency/213525"]There seems to be no link listed first.[/quote]

I fixed the links.

[quote userid="72172" url="~/f/nordic-q-a/52893/pwm-output-with-stable-frequency/213526"]Is it possible to select LFCLK (XTAL) with "pwm_library" or "pwm_driver"?[/quote]

For PWM in pwm_library / pwm_driver, it's the HFCLK that decides how stable the frequency is. Use nrf_drv_clock_hfclk_request() to request high-accuracy(HFXO) source HFCLK.

RE: PWM output with stable frequency

takashina hiroki — Sun, 06 Oct 2019 23:56:55 GMT

I'm sorry.
I forgot to talk about one important thing.

I want to select LFCLK (XTAL) as the PWM clock source.
Is it possible to select LFCLK (XTAL) with "pwm_library" or "pwm_driver"?

RE: PWM output with stable frequency

takashina hiroki — Sun, 06 Oct 2019 23:08:48 GMT

Thank you for answering.

There seems to be no link listed first.
Please let me know if there are similar links.

RE: PWM output with stable frequency

Sigurd — Fri, 04 Oct 2019 15:45:02 GMT

Hi,

[quote user=""]Is there a way to perform stable PWM output regardless of other factors such as interrupts?[/quote]

Yes, you should checkout the pwm_library instead(uses TIMER+GPIOTE+PPI). See this and this link.

[quote user=""]Is it possible to output PWM at the hardware level?[/quote]

Yes, we also have dedicated PWM hardware on the nRF52 series. The pwm_driver uses that. See this link.