Zephyr related - how to disable (uart-) shell during runtime?

[uknoblic]

Hi,

as i would like to use the uart shell for production purposes as well (e.g. setting the devices serial number) - how can i turn off the shell at runtime (in order to enter low power mode and measure the device's current consumption)? As the shell is startet automatically using SYS_INIT(), i would assume that calling shell_uninit() should disable it again, but the current consumption is still to high.

Regards

Ulf

[uknoblic]

Hi, i found the reason for this - if the ASYNC api is used, rx is not disabled when the uart instance is un-initialized (shell_uninit() -> instance_uninit() -> async_uninit() (which is empty)). Need to call rx_disable on the device manually to fully disable the shell.

[Vidar Berg]

Thanks for the update. Calling rx_disable() is not always sufficient to ensure low power when using 'nordic,nrf-uarte' (the HF clock request may not be released - ref. Low power). A workaround can be to enable CONFIG_PM_DEVICE=y in your project configuration and run PM_DEVICE_ACTION_SUSPEND on the UART device after un-initializing the shell: https://github.com/nrfconnect/sdk-zephyr/blob/4040aa0bf581206dd68beb0758b39096342ee7e0/drivers/serial/uart_nrfx_uarte.c#L1891 

 RE: How to put the UART to sleep (low power mode)  

[uknoblic]

Thank you Vidar, i was already using CONFIG_PM_DEVICE  / PM_DEVICE_ACTION_SUSPEND, but calling uart_rx_disable finaly solved this issue ;-)

[Vidar Berg]

Sorry, I misread the function name and thought you were using the UARTE HAL to write to the UARTE->ENABLE register. rx_disable -> uarte_nrfx_rx_disable() will properly disable UART reception and cause the idle current to drop to around 20 uA. Note that PM_DEVICE_ACTION_SUSPEND will also disable the peripheral, which should reduce the idle current further.