Controlling the nrf9151 feather with external MCU via UART and AT Commands

gav_ncl

Hi,

I have been using the nrf9151 feather and have managed to flash the blinky example no problem.

I am now trying to flash the at_client sample and use pins P0.23/P0.24 to control the modem with serial AT commands as opposed to the serial via USB.

Serial data works fine through USB but when I switch to the Rx/Tx pins on the board I get an output but it makes no sense. The board is powered using the USB during my testing.

The only thing I have changed in the sample code is to redirect uart1 to those pins as follows. Any suggestions would be appreciated.

&uart1 {
status = “okay”;
current-speed = <115200>;

pinctrl-0 = <&uart1_default>;
pinctrl-1 = <&uart1_sleep>;
pinctrl-names = "default", "sleep";

};

&pinctrl {
uart1_default: uart1_default {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 24)>, <NRF_PSEL(UART_RX, 0, 23)>;
};
group2 {
psels = <NRF_PSEL(UART_TX, 0, 24)>, <NRF_PSEL(UART_RX, 0, 23)>;
};
};

uart1_sleep: uart1_sleep {
	group1 {
		psels = <NRF_PSEL(UART_TX, 0, 24)>, <NRF_PSEL(UART_RX, 0, 23)>;
		low-power-enable;
	};
};

};

AchimKraus

Are you sure, that the at_client uses UART1 and not UART0?

gav_ncl

Yes I think it does use UART0 for serial via the USB port. I have tried reconfiguring the UART0 to map to pins 23/24 (TX/RX header) like above but it results it errors in the build process. I assumed the above would overide UART0 but maybe this is not the case? Essentially I am just trying to configure two pint on the headers of the feather board to be UART Tx and Rx so I can talk to the board without going via the USB port. I plan on talking to the feather with another MCU and provide power to VBAT. I am quite new to nrf9151 but managed to get the same working on the nrf9151DK but I appreciate this board will be a bit different.

Any suggestions for this would be great.
Thanks
Gavin

AchimKraus

	uart0_default: uart0_default {
		group1 {
			psels = <NRF_PSEL(UART_TX, 0, 11)>,
					<NRF_PSEL(UART_RX, 0, 10)>;
		};
	};

	uart0_sleep: uart0_sleep {
		group1 {
			psels = <NRF_PSEL(UART_TX, 0, 11)>,
					<NRF_PSEL(UART_RX, 0, 10)>;
			low-power-enable;
		};
	};

	uart1_default: uart1_default {
		group1 {
			psels = <NRF_PSEL(UART_TX, 0, 24)>,
					<NRF_PSEL(UART_RX, 0, 23)>;
		};
	};

	uart1_sleep: uart1_sleep {
		group1 {
			psels = <NRF_PSEL(UART_TX, 0, 24)>,
					<NRF_PSEL(UART_RX, 0, 23)>;
			low-power-enable;
		};
	};

So I guess, if you just configure uart0 to p0.23 and p0.24, that is in conflict with uart1. You would need to change uart1 as well, maybe just exchange the pinctrls in the uart defs, e.g.

&uart0 {
	pinctrl-0 = <&uart1_default>;
	pinctrl-1 = <&uart1_sleep>;
};

&uart1 {
	pinctrl-0 = <&uart0_default>;
	pinctrl-1 = <&uart0_sleep>;
};

Alternatively, you may check, which UART is chosen. I guess, it’s in “nrf/lib/at_host/at_host.c”:

#define AT_HOST_UART_DEV_GET()                                                                     \
	DEVICE_DT_GET(COND_CODE_1(DT_HAS_CHOSEN(ncs_at_host_uart),                                 \
		(DT_CHOSEN(ncs_at_host_uart)), (DT_NODELABEL(uart0))))

So you may need to add a

/ {
	chosen {
		ncs,at-host-uart = &uart1;
	};