Zephyr PWM and GPIO in System Off

[Airat]

Hi,

I am developing on a nRF52840dk. I control a LED2 (line P0.14) with PWM in normal operation and want to leave the LED2 ON when I go to System Off mode.

I tried setting the line to constant active with the Zephyr PWM driver by setting the pulse equal to period.

I tried setting the line to constant inactive with the Zephyr PWM driver by setting the pulse equal to 0 and then setting the active level with the GPIO driver.

In both cases the LED was off after going to System Off.

I can't find any obvious way to do what I want.

[Airat]

Including PWM driver by CONFIG_PWM=y seems to force the GPIO pin to be configured to OUTPUT with low level (regardless if it's active high or low). And it matches with the requirements from documentation on the PWM peripheral https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fpwm.html&cp=4_0_0_5_16_3&anchor=concept_ckf_5qw_nr

It looks like the device sets the GPIO pin to 0 before going to System Off.

Interestingly, if I add nordic,invert; to pwm0_sleep then the LED is always off in System Off mode.

Is there a way to control that behavior just before going to System Off? Or will I need to drop usage of the Zephyr PWM driver?  

[Sigurd]

Airat said:

Interestingly, if I add nordic,invert; to pwm0_sleep then the LED is always off in System Off mode.

Is there a way to control that behavior just before going to System Off? Or will I need to drop usage of the Zephyr PWM driver?  

So it's not enough to set the desired level with/without nordic,invert; to pwm0_sleep ? You want to change it based on something at run-time?

[Airat]

Yes, exactly. I need an option for choosing LED to be on or off in System Off mode in a run-time.

[Sigurd]

Hi,

Looks like it's the device driver Power Management implementation that sets the pin to this state as part of the process of going into System Off mode. I haven't tested it, but something like this might work to avoid that:

1) ret = pm_device_action_run(pwm, PM_DEVICE_ACTION_SUSPEND); // unit the PWM
2) ret = pm_device_state_lock(pwm); // Lock the PWM DEVICE

3) Use GPIO API to set the pin as you like

4) Enter system off mode

[Airat]

Thank you, that did what I wanted.

To note GPIO must be configured to output after locking the PWM device, as it sets the PIN_CNF to the default state (0x20).