Dynamic UART0 PIN change for communicating with multiple (3) UART devices connected at different PINs

[vinodsdw]

Hello,

  I want to change the UART0  RX/TX pins at run time because I am having 3 UART devices connected to the nrf5340 at different RX/TX pins.

I am already using I2C, SPI etc so I am having only UART0 available and I will not be communicating with all the three devices at same time, instead based on use case I will be selecting one of these three devices. So using single UART0 should work for me and I should be able to change the PINs of the UART0 RX/TX at RUN time, any time while the code is running. 

And it is not for one time, I should be able to switch it between any of these three UART devices multiple times and not only at the time of BOOTUP.

How can I achieve this with this zephyr ?

Is there any way to change the PINs of same UART at runtime ?

[Kenneth]

Hello,

This is not straight forward, but I have some suggestions.

The main problem here is that it's not possible to dynamically update the pin configuration, this is not directly supported in software, and it's also not possible in hardware while a peripheral is enabled. 

But there might be a way around this, at least for uart.

If you use CONFIG_PM_DEVICE=y, then you have the option to call for instance pm_device_action_run(uart_dev, PM_DEVICE_ACTION_RESUME) and pm_device_action_run(uart_dev, PM_DEVICE_ACTION_SUSPEND).
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/services/pm/api/index.html#c.pm_device_action_run 

So the above you can enable and disable the UART.

Next step is to update the pins while it's disabled (SUSPEND), it looks like you can use the pinctrl_apply_state() to do this:
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/hardware/pinctrl/index.html#dynamic-pin-control 

So the above will update the pins.

There is now one final problem, when you now switch to RESUME the driver will automatically apply the default state, ref:
https://github.com/nrfconnect/sdk-zephyr/blob/main/drivers/serial/uart_nrfx_uarte.c#LL1853C7-L1853C30 

However I can see from the above that it's possible to avoid this by a kconfig option, for instance set:
CONFIG_UART_0_GPIO_MANAGEMENT=n
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/kconfig/index.html#CONFIG_UART_0_GPIO_MANAGEMENT

Kennet