nRF54L15 UART20 on non-standard pins results in garbage data

RE: nRF54L15 UART20 on non-standard pins results in garbage data

amovitz — Mon, 07 Jul 2025 19:14:36 GMT

Found a mistake in my last follow up - For my setup I need to rearrange a few things. The pins above are the new mapping.

UART20->UART00
SPI00->SPI20

This allows me to use UART and SPI without making too many hardware changes. The following is my working overlay. I still may try to use a logging thread but I'm going to stick with immediate mode for now. UART is not necessarily critical to the final product, but it is very important for development.

/*
 * Copyright (c) 2025 Alex Movitz
 *
 * SPDX-License-Identifier: N/A
 */

/ {
	model = "Smart Dental Probe";
	compatible = "nordic,nrf54l15dk_nrf54l15-cpuapp";

	zephyr,user {
		io-channels = <&adc 0>, <&adc 1>;
	};

	// Remove nodes added in dev kit dtsi
    /delete-node/ aliases;
    /delete-node/ chosen;
	/delete-node/ leds;
    /delete-node/ pwmleds;

    aliases {
		watchdog0 = &wdt31;
        vibrator = &vibrator;
        buzzer = &buzzer;
		sw0 = &button0;
		sw1 = &button1;
		sw2 = &button2;
		sw3 = &button3;
		sw4 = &button4;
		joystick = &adc;
    };

	chosen {
		zephyr,bt-hci = &bt_hci_controller;
		zephyr,entropy = &rng;
		zephyr,console = &uart00;
		zephyr,shell-uart = &uart00;
		zephyr,uart-mcumgr = &uart00;
		zephyr,flash-controller = &rram_controller;
		zephyr,flash = &cpuapp_rram;
		zephyr,code-partition = &slot0_partition;
		zephyr,sram = &cpuapp_sram;
	};

	output: out0 {
		compatible = "gpio-leds";
		status = "okay";
	
		vibrator: vibrator {
			gpios = <&gpio1 10 (GPIO_PULL_DOWN | GPIO_ACTIVE_HIGH)>;
			label = "VIBRATOR";
		};
	
		buzzer: buzzer {
			gpios = <&gpio1 9 (GPIO_PULL_DOWN | GPIO_ACTIVE_HIGH)>;
			label = "BUZZER";
		};
	};

    buttons: buttons {
        compatible = "gpio-keys";
        status = "okay";
		button_t_f: button_0 {
			gpios = <&gpio0 0 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Top Front Button";
			zephyr,code = <INPUT_KEY_0>;
		};
		button_t_r: button_1 {
			gpios = <&gpio0 1 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Top Rear Button";
			zephyr,code = <INPUT_KEY_1>;
		};
		button_b_f: button_2 {
			gpios = <&gpio0 2 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Bottom Front Button";
			zephyr,code = <INPUT_KEY_0>;
		};
		button_b_r: button_3 {
			gpios = <&gpio0 3 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Bottom Rear Button";
			zephyr,code = <INPUT_KEY_1>;
		};
		button4: button_c: button_4 {
			gpios = <&gpio0 4 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Center Button";
			zephyr,code = <INPUT_KEY_2>;
		};
    };
};

&adc {
	#address-cells = <1>;
	#size-cells = <0>;
	label = "Joystick ADC";

	channel@0 {
		reg = <0>;
		zephyr,gain = "ADC_GAIN_1";
		zephyr,reference = "ADC_REF_INTERNAL";
		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_SAADC_AIN0>; /* P1.04 */
		zephyr,resolution = <12>;
		zephyr,oversampling = <8>;
	};

	channel@1 {
		reg = <1>;
		zephyr,gain = "ADC_GAIN_1";
		zephyr,reference = "ADC_REF_INTERNAL";
		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_SAADC_AIN1>; /* P1.05 */
		zephyr,resolution = <12>;
		zephyr,oversampling = <8>;
	};
};

&i2c21 {
	compatible = "nordic,nrf-twim";
	status = "okay";
	pinctrl-0 = <&i2c21_default>;
	pinctrl-1 = <&i2c21_sleep>;
	pinctrl-names = "default", "sleep";
	clock-frequency = <I2C_BITRATE_FAST>;

	lsm6ds3tr_c: lsm6ds3tr-c@6a {
		compatible = "st,lsm6dsl";
		reg = <0x6a>;
		irq-gpios = <&gpio1 6 GPIO_ACTIVE_HIGH>;
		status = "okay";
	};

    ssd1306@3c {
        compatible = "solomon,ssd1306fb";
        reg = <0x3c>;
        label = "SSD1306";
        height = <64>;
        width  = <128>;
        segment-offset  = <0>;
        page-offset     = <0>;
        display-offset  = <0>;
        multiplex-ratio = <63>;
        prechargep      = <0x22>;
        segment-remap;
        com-invdir;
        com-sequential;
		reset-gpios = <&gpio1 3 GPIO_ACTIVE_HIGH>;
		status = "okay";
    };
};

&gpio0 {
    status = "okay";
};

&gpio1 {
    status = "okay";
};

&gpio2 {
    status = "okay";
};

&uart20 {
	status = "disabled";
};

&uart00 {
	status = "okay";
	pinctrl-0 = < &uart00_default >;
	pinctrl-1 = < &uart00_sleep >;
	pinctrl-names = "default", "sleep";
	current-speed = < 115200 >;
	// endtx-stoptx-supported;
	// frame-timeout-supported;
	// /delete-property/ endtx-stoptx-supported;
	// /delete-property/ frame-timeout-supported;
};

&uart30 {
	status = "disabled";
};


// Disable NFC
&uicr {
	nfct-pins-as-gpios;
};

// SD Card
&spi00 {
	status = "disabled";

	/delete-node/ mx25r64;
};

&spi20 {
	status = "okay";
	cs-gpios = <&gpio2 10 GPIO_ACTIVE_LOW>;
	pinctrl-0 = < &spi20_default >;
	pinctrl-1 = < &spi20_sleep >;
	pinctrl-names = "default", "sleep";

	// SDHC
	sdhc0: sdhc@0 {
		compatible = "zephyr,sdhc-spi-slot";
		reg = <0>;
		status = "okay";
		label = "SDHC0";
		spi-max-frequency = <8000000>;
	};
};

// Define Pins
&pinctrl {
	i2c21_default: i2c21_default {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 2, 0)>,
					<NRF_PSEL(TWIM_SCL, 2, 1)>;
			bias-pull-up;
			nordic,drive-mode = <NRF_DRIVE_S0D1>;				
		};
	};
	i2c21_sleep: i2c21_sleep {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 2, 0)>,
				<NRF_PSEL(TWIM_SCL, 2, 1)>;
			low-power-enable;
		};
	};	

	uart00_default: uart00_default {
		group1 {
			psels = <NRF_PSEL(UART_TX, 2, 2)>;
		};
		group2 {
			psels = <NRF_PSEL(UART_RX, 2, 7)>;
			bias-pull-up;
		};
	};
	uart00_sleep: uart00_sleep {
		group1 {
			psels = <NRF_PSEL(UART_TX, 2, 2)>,
					<NRF_PSEL(UART_RX, 2, 7)>;
			low-power-enable;
		};
	};


	spi20_default: spi20_default {
		group1 {
			psels = <NRF_PSEL(SPIM_SCK, 2, 6)>,
					<NRF_PSEL(SPIM_MISO, 2, 9)>,
					<NRF_PSEL(SPIM_MOSI, 2, 8)>;
		};
	};
	spi20_sleep: spi20_sleep {
		group1 {
			psels = <NRF_PSEL(SPIM_SCK, 2, 6)>,
					<NRF_PSEL(SPIM_MISO, 2, 9)>,
					<NRF_PSEL(SPIM_MOSI, 2, 8)>;
			low-power-enable;
		};
	};
};

RE: nRF54L15 UART20 on non-standard pins results in garbage data

amovitz — Mon, 07 Jul 2025 18:31:45 GMT

So if I'm reading the pin assignment table correctly, pins on P2 have special dedications. Should I make the following changes to correctly assign with the power domain constraints?
UART20
TXD -> P2.02 (no change)
RXD -> P2.07
SPI00/SDHC
CLK -> P2.06 (no change)
MISO -> P2.08
MOSI -> P2.09
CS -> P2.10

I tried these changes and stopped getting clobbered output only when I changed from a logging thread to an immediate log mode, but I still don't get any feedback on RXD, even on P2.07.

/*
 * Copyright (c) 2025 Alex Movitz
 *
 * SPDX-License-Identifier: N/A
 */

/ {
	model = "Smart Dental Probe";
	compatible = "nordic,nrf54l15dk_nrf54l15-cpuapp";

	zephyr,user {
		io-channels = <&adc 0>, <&adc 1>;
	};

	// Remove nodes added in dev kit dtsi
    /delete-node/ aliases;
    /delete-node/ chosen;
	/delete-node/ leds;
    /delete-node/ pwmleds;

    aliases {
		watchdog0 = &wdt31;
        vibrator = &vibrator;
        buzzer = &buzzer;
		sw0 = &button0;
		sw1 = &button1;
		sw2 = &button2;
		sw3 = &button3;
		sw4 = &button4;
		joystick = &adc;
    };

	chosen {
		zephyr,bt-hci = &bt_hci_controller;
		zephyr,entropy = &rng;
		zephyr,console = &uart20;
		zephyr,shell-uart = &uart20;
		zephyr,uart-mcumgr = &uart20;
		zephyr,flash-controller = &rram_controller;
		zephyr,flash = &cpuapp_rram;
		zephyr,code-partition = &slot0_partition;
		zephyr,sram = &cpuapp_sram;
	};

	output: out0 {
		compatible = "gpio-leds";
		status = "okay";
	
		vibrator: vibrator {
			gpios = <&gpio1 10 (GPIO_PULL_DOWN | GPIO_ACTIVE_HIGH)>;
			label = "VIBRATOR";
		};
	
		buzzer: buzzer {
			gpios = <&gpio1 9 (GPIO_PULL_DOWN | GPIO_ACTIVE_HIGH)>;
			label = "BUZZER";
		};
	};

    buttons: buttons {
        compatible = "gpio-keys";
        status = "okay";
		button_t_f: button_0 {
			gpios = <&gpio0 0 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Top Front Button";
			zephyr,code = <INPUT_KEY_0>;
		};
		button_t_r: button_1 {
			gpios = <&gpio0 1 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Top Rear Button";
			zephyr,code = <INPUT_KEY_1>;
		};
		button_b_f: button_2 {
			gpios = <&gpio0 2 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Bottom Front Button";
			zephyr,code = <INPUT_KEY_0>;
		};
		button_b_r: button_3 {
			gpios = <&gpio0 3 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Bottom Rear Button";
			zephyr,code = <INPUT_KEY_1>;
		};
		button4: button_c: button_4 {
			gpios = <&gpio0 4 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
			label = "Center Button";
			zephyr,code = <INPUT_KEY_2>;
		};
    };
};

&adc {
	#address-cells = <1>;
	#size-cells = <0>;
	label = "Joystick ADC";

	channel@0 {
		reg = <0>;
		zephyr,gain = "ADC_GAIN_1";
		zephyr,reference = "ADC_REF_INTERNAL";
		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_SAADC_AIN0>; /* P1.04 */
		zephyr,resolution = <12>;
		zephyr,oversampling = <8>;
	};

	channel@1 {
		reg = <1>;
		zephyr,gain = "ADC_GAIN_1";
		zephyr,reference = "ADC_REF_INTERNAL";
		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_SAADC_AIN1>; /* P1.05 */
		zephyr,resolution = <12>;
		zephyr,oversampling = <8>;
	};
};

&i2c21 {
	compatible = "nordic,nrf-twim";
	status = "okay";
	pinctrl-0 = <&i2c21_default>;
	pinctrl-1 = <&i2c21_sleep>;
	pinctrl-names = "default", "sleep";
	clock-frequency = <I2C_BITRATE_FAST>;

	lsm6ds3tr_c: lsm6ds3tr-c@6a {
		compatible = "st,lsm6dsl";
		reg = <0x6a>;
		irq-gpios = <&gpio1 6 GPIO_ACTIVE_HIGH>;
		status = "okay";
	};

    ssd1306@3c {
        compatible = "solomon,ssd1306fb";
        reg = <0x3c>;
        label = "SSD1306";
        height = <64>;
        width  = <128>;
        segment-offset  = <0>;
        page-offset     = <0>;
        display-offset  = <0>;
        multiplex-ratio = <63>;
        prechargep      = <0x22>;
        segment-remap;
        com-invdir;
        com-sequential;
		reset-gpios = <&gpio1 3 GPIO_ACTIVE_HIGH>;
		status = "okay";
    };
};

&gpio0 {
    status = "okay";
};

&gpio1 {
    status = "okay";
};

&gpio2 {
    status = "okay";
};

&uart20 {
	status = "okay";
	pinctrl-0 = < &uart20_default >;
	pinctrl-1 = < &uart20_sleep >;
	pinctrl-names = "default", "sleep";
	current-speed = < 115200 >;
	// endtx-stoptx-supported;
	// frame-timeout-supported;
	// /delete-property/ endtx-stoptx-supported;
	// /delete-property/ frame-timeout-supported;
};

&uart30 {
	status = "disabled";
};


// Disable NFC
&uicr {
	nfct-pins-as-gpios;
};

// SD Card
&spi00 {
	status = "okay";
	cs-gpios = <&gpio2 10 GPIO_ACTIVE_LOW>;
	pinctrl-0 = < &spi00_default >;
	pinctrl-1 = < &spi00_sleep >;

	// Disable SPI NOR
	mx25r64: mx25r6435f@0 {
		status = "disabled";
	};

	// SDHC
	sdhc0: sdhc@0 {
		compatible = "zephyr,sdhc-spi-slot";
		reg = <0>;
		status = "okay";
		label = "SDHC0";
		spi-max-frequency = <8000000>;
	};
};

// Define Pins
&pinctrl {
	i2c21_default: i2c21_default {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 2, 0)>,
					<NRF_PSEL(TWIM_SCL, 2, 1)>;
			bias-pull-up;
			nordic,drive-mode = <NRF_DRIVE_S0D1>;				
		};
	};
	i2c21_sleep: i2c21_sleep {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 2, 0)>,
				<NRF_PSEL(TWIM_SCL, 2, 1)>;
			low-power-enable;
		};
	};	

	uart20_default: uart20_default {
		group1 {
			psels = <NRF_PSEL(UART_TX, 2, 2)>;
		};
		group2 {
			psels = <NRF_PSEL(UART_RX, 2, 7)>;
			bias-pull-up;
		};
	};
	uart20_sleep: uart20_sleep {
		group1 {
			psels = <NRF_PSEL(UART_TX, 2, 2)>,
					<NRF_PSEL(UART_RX, 2, 7)>;
			low-power-enable;
		};
	};


	spi00_default: spi00_default {
		group1 {
			psels = <NRF_PSEL(SPIM_SCK, 2, 6)>,
					<NRF_PSEL(SPIM_MISO, 2, 9)>,
					<NRF_PSEL(SPIM_MOSI, 2, 8)>;
		};
	};
	spi00_sleep: spi00_sleep {
		group1 {
			psels = <NRF_PSEL(SPIM_SCK, 2, 6)>,
					<NRF_PSEL(SPIM_MISO, 2, 9)>,
					<NRF_PSEL(SPIM_MOSI, 2, 8)>;
			low-power-enable;
		};
	};
};

CONFIG_LOG_MODE_IMMEDIATE=y
CONFIG_LOG_MODE_OVERFLOW=n
# CONFIG_LOG_PROCESS_TRIGGER_THRESHOLD=10
# CONFIG_LOG_PROCESS_THREAD=y
# CONFIG_LOG_PROCESS_THREAD_SLEEP_MS=1000
# CONFIG_LOG_PROCESS_THREAD_STACK_SIZE=768
# CONFIG_LOG_BUFFER_SIZE=1024

RE: nRF54L15 UART20 on non-standard pins results in garbage data

Maria Gilje — Mon, 07 Jul 2025 13:55:40 GMT

Hi,

Please refer to the documentation on Dedicated pins and Cross power-domain use and the relevant pin assignment table for your package variant. Sorry that this was so short, I'll be able to elaborate later if the linked documentation is not enough.

Best regards,

Maria