Issue with UART when using RTT Zephyr Shell

[Alex P]

Dear Team,

I am using NRF54L15 DK, where I have UART defined and mapped as following:

    uart20_default: uart20_default {

        group1 {

            psels = <NRF_PSEL(UART_TX, 1, 9)>,

                <NRF_PSEL(UART_RX, 1, 7)>;

            bias-pull-up;

        };

    };

    /* UART20 sleep state */

    uart20_sleep: uart20_sleep {

        group1 {

            psels = <NRF_PSEL(UART_TX, 1, 9)>,

                <NRF_PSEL(UART_RX, 1, 7)>;

            low-power-enable;

        };

    };

&uart20 {

    compatible = "nordic,nrf-uarte";

    status = "okay";

    current-speed = <115200>;

    pinctrl-0 = <&uart20_default>;

    pinctrl-1 = <&uart20_sleep>;

    pinctrl-names = "default", "sleep";

};

This UART is connected to a test terminal on my laptop.

I am able to initialize UART and it works just fine, but only for output (e.g. when using uart_poll_out command).

No matter how well I tried (eg. uart_poll_in, interrupt-driven or asynchronous mode),  I was not able to make UART to receive any data.

What I have noticed though, is that (somehow!) whatever is being sent to that UART port from terminal, gets intercepted by Zephyr shell, which tries to execute the shell commands and responds back over my UART.

It is quite weird, because my shell is currently configured for RTT mode.

Here are my related settings from prj.conf:

CONFIG_CONSOLE=y

CONFIG_LOG=y

CONFIG_LOG_BACKEND_RTT=y

CONFIG_USE_SEGGER_RTT=y

CONFIG_RTT_CONSOLE=y

CONFIG_UART_CONSOLE=n

CONFIG_LOG_BACKEND_UART=n

CONFIG_SERIAL=y

CONFIG_UART_NRFX=y

Please assist. Is this only a DK related issue? 

Thanks

[Sigurd]

Hi!
Try this overlay:

	uart20_default: uart20_default {
		group1 {
			psels = <NRF_PSEL(UART_TX, 1, 9)>,
		};

		group2 {
			psels = <NRF_PSEL(UART_RX, 1, 7)>,
			bias-pull-up;
		};
	};

	uart20_sleep: uart20_sleep {
		group1 {
			psels = <NRF_PSEL(UART_TX, 1, 9)>,
				<NRF_PSEL(UART_RX, 1, 7)>,
			low-power-enable;
		};
	};

[Alex P]

Hi Sigurd,

I have tried (but also even completely removing bias-pull-up), but nothing has changed, really.

I would later need to use the same port in half duplex mode, too.

Is there anything else can be done?

Thanks

WBR,

Alex

[Sigurd]

Hi!

NRF_PSEL(UART_TX, 1, 9)

Any reason for why you are using this pin? Could you try a different pin ? P1.9 is connected to Button 1 on the DK

[Alex P]

I can certainly try, however, there is no issue with UART_TX (it works just fine). I have an issue with UART_RX being intercepted by Zephyr shell, so not sure how your proposal is relevant in this context.

[Sigurd]

Another thing you can double-check, is that you have CONFIG_SHELL_BACKEND_SERIAL=n