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  • Case ID: 340227
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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
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  • 0

    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

  • 0 in reply to Vidar Berg

    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!

  • 0 in reply to Piziwate

    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;
}

  • 0 in reply to Vidar Berg

    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.

  • 0 in reply to 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)));
    ...
    disabling PM_DEVICE and PM_DEVICE_RUNTIME re-enables the shell. Please advise.
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