Power Management stopped shell working on uart0

[Piziwate]

Hello,

I'm trying to implement runtime power management (SDK 2.9.0), but as soon as I enable the option, the shell and logging on UART0 stop working at startup. The rest of the system functions normally.The status of UART0 is active, and I have never put it in standby.

Do you have any idea what might be causing this?

Changed configuration options :

CONFIG_PM_DEVICE=y

CONFIG_PM_DEVICE_RUNTIME=y

If I remove these two lines, everything works fine...

BR

[Vidar Berg]

Hello,

When having shell enabled you usually want the application to control when the UART is suspended through PM actions, and this only requires CONFIG_PM_DEVICE device to be enabled. CONFIG_PM_DEVICE_RUNTIME is not needed for this.

Is the CONFIG_UART_0_NRF_ASYNC_LOW_POWER symbol selected in your configuration file (build/<application name>/zephyr/.config)? From looking at the driver it looks like the UART should only be auto suspended on idle if you have both CONFIG_PM_DEVICE_RUNTIME and CONFIG_UART_0_NRF_ASYNC_LOW_POWER enabled.

Best regards,

Vidar

[Piziwate]

Thank you for your response. I confirm that CONFIG_UART_0_NRF_ASYNC_LOW_POWER is not enabled (besides, I am not using the UART_ASYNC_API mode).

So I wonder why I have no logs and no shell.

At startup, I only get this:
Booting TF-M v2.1.1-ncs2-snapshot1
[Sec Thread] Secure image initializing!

[Vidar Berg]

Thanks for confirming. It turns out there is a bug in the runtime pm with the interrupt driven API. Fix has been added upstream here: https://github.com/zephyrproject-rtos/zephyr/pull/81631. The application must also call pm_device_runtime_get(shell_dev) to signal the pm subsystem to not suspend the shell interface. I would consider disabling CONFIG_PM_DEVICE_RUNTIME and use PM actions instead:

/* Disable shell interface */
err = pm_device_action_run(shell_dev, PM_DEVICE_ACTION_SUSPEND);
if (err) {
	LOG_ERR("Failed to suspend uart (err: %d)", err);
	return;
}

[timl2415]

Hi Vidar,

I'm also running into a similar issue where we I have an application where we enable PM_DEVICE_RUNTIME to minimize power consumption. We can't seem to enable logs/shell with PM_DEVICE_RUNTIME enabled even after cherry-picking the change to our ncs 2.9.0 installation and calling:

pm_device_runtime_get(DEVICE_DT_GET(DT_CHOSEN(zephyr_shell_uart)));

Is the commit dependent on another upstream commit (relative to 2.9.0)? I'll try to reproduce on a nrf5340dk and sample app.

[timl2415]

I added the following to the zephyr shell_module sample on top of a clean ncs 2.9.0 installation and the shell prompt still wouldn't come up:

- added to prj.conf

CONFIG_PM_DEVICE=y

CONFIG_PM_DEVICE_RUNTIME=y

- added to src/main.c

#include <zephyr/pm/device_runtime.h>

int main(void)

{

pm_device_runtime_get(DEVICE_DT_GET(DT_CHOSEN(zephyr_shell_uart)));

...

- cherry-picked https://github.com/zephyrproject-rtos/zephyr/pull/81631 changes

disabling PM_DEVICE and PM_DEVICE_RUNTIME re-enables the shell. Please advise.

[Vidar Berg]

Please try the modified shell_module sample below with the v3.0.0preview2 tag of the SKD (includes commit from https://github.com/zephyrproject-rtos/zephyr/pull/81631). 

Enable PM runtime feature for UARTE driver in Devictree:

Modified code

2804.shell_module.zip

[timl2415]

Hi Vidar,

I confirmed the modified example works, although I was trying to backport the fixes back to NCS 2.9.0 and I believe the fix is actually in https://github.com/zephyrproject-rtos/zephyr/pull/81533. Applying this commit as a patch alone in 2.9.0 fixes the uart shell when PM_DEVICE_RUNTIME is enabled, I also didn't have to edit my devicetree or call pm_device_runtime_get.