Generate PWM frequency smaller than 4Hz.

[SnaiderBG]

Hi everybody, I'm looking to build a PWM generator with 2 outputs from 1-100Hz. Unfurtunately the current PWM API examples with Zephyr works only for 4-100Hz.

I've tried the sw_pwm but I'm not able to generate the PWM signals for 2 custom outputs. Other approach we have look intois the use of advanced pwm. Are we able to achieve 1 Hz with the Zephyr SDK? In case we are not, what approach is the best to follow?

We are using SDK 2.8.0

[Susheel Nuguru]

Have not tried this myself with sw_pwm, but what is the the error you are getting if you try to do this for 2 custom outputs? I am assuming that you have it working to get 1 Hz for 1 custom output? 

Maybe use of nrfx_pwm API can be give you more control on configurations of what prescalar you want to put for timing?

[SnaiderBG]

With the sw_pwm, we are having issues mainly with the device tree, it works for the predefined node pwm_led0 but when we try to use another it doesn't work. In the case we use the nrfx_pwm what considerations should we have, with the device tree and configurations. Can we still use other pwms with the zephyr pwm API?

[Kenneth]

The hardware does not support this low frequency.

The zephyr driver unfortunately doesn’t iterate through all possible software PWM nodes in the device tree and just works off of the 0th one.

https://github.com/zephyrproject-rtos/zephyr/blob/e60da1bd640a37370870a83277142dd560f1fb8d/drivers/pwm/pwm_nrf_sw.c#L428

Kenneth