Adafruit nRF52840 Feather Express GPIO and DTS

RE: Adafruit nRF52840 Feather Express GPIO and DTS

bluetoothmdw — Fri, 14 Nov 2025 05:26:13 GMT

Benjamin, thank you so much for this. Happily, last night I'd managed to arrive at some similar conclusions (although I ended up with the macro GPIO_DT_SPEC_GET_OR so I need to make sure I'm clear on the difference between this macro and GPIO_DT_SPEC_GET. I haven't tested yet but it's very reassuring to see your code fragments looking so similar to what I currently have.

So, next step is testing this in a simple application and then, per your suggestion, more work in the excellent DevAcademy!

Thanks once again, Much appreciated :-)

Martin

RE: Adafruit nRF52840 Feather Express GPIO and DTS

Benjamin — Thu, 13 Nov 2025 21:57:01 GMT

Hi Martin,

Welcome to Nordic, it seems like you are on a good trajectory already!

I can answer some of your questions, but the best way to learn is continuing the DevAcademy and browsing the samples available in our SDK. There are also a ton of resources available in the documentation (Nordic TechDocs and Zephyr Project Docs).

[quote user=""]Put something in a DTS overlay file?[/quote]

Yes, you need to define the GPIO pin in the device tree. Overlays let you avoid editing the main device tree files for the SoC and board. In an overlay, create a node for your GPIO pin. A generic GPIO pin node can look like this:

/ {
    my_pin: my_pin_node {
        compatible = "nordic,gpio-pins";
        gpios = <&gpio0 25 GPIO_ACTIVE_HIGH>;
        status = "okay";
    };
};

[quote user=""]What do I need to do to make the pin accessible from my C code?[/quote]

To access the pin from your C code you need a device pointer. Here is a simple code snippet that creates a device pointer with the use of a thin wrapper:

static const struct gpio_dt_spec my_pin = GPIO_DT_SPEC_GET(DT_NODELABEL(my_pin), gpios);

To make use of it you need to initialize and configure it. Here is a bare minimum example that just toggles a pin:

int main(void)
{
    device_is_ready(my_pin.port)

    gpio_pin_configure_dt(&my_pin, GPIO_OUTPUT_INACTIVE)

    while (1) {
        gpio_pin_toggle_dt(&my_pin);
        k_sleep(K_MSEC(500));
    }

    return 0;
}

[quote user=""]Is the DTS file for the board basically incomplete?[/quote]

No, it is not incomplete. Devictree is hierarchical and most nodes lives inside these included files:

#include "adafruit_feather_nrf52840_common.dtsi"
#include <nordic/nrf52840_partition.dtsi>

To communicate over UART using two GPIO pins, you should check out Lesson 5 – Serial communication (UART) and other relevant samples.

Best regards,
Benjamin

RE: Adafruit nRF52840 Feather Express GPIO and DTS

bluetoothmdw — Wed, 12 Nov 2025 19:04:25 GMT

The Nordic DevAcademy is doing a good job of educating me on the subject of the Zephyr Device Tree!

I've found the DTS definition for a node called connector which has a label of feather_header. In there, I see a property called gpio-map which includes values for all the header pins, including the one I want to write to:

<10 0 &gpio0 25 0>, /* TXD */

/*
 * Copyright (c) 2020 Richard Osterloh <richard.osterloh@gmail.com>
 *
 * SPDX-License-Identifier: Apache-2.0
 */

/ {
	feather_header: connector {
		compatible = "adafruit-feather-header";
		#gpio-cells = <2>;
		gpio-map-mask = <0xffffffff 0xffffffc0>;
		gpio-map-pass-thru = <0 0x3f>;
		gpio-map = <0 0 &gpio0 4 0>,	/* A0 */
			   <1 0 &gpio0 5 0>,	/* A1 */
			   <2 0 &gpio0 30 0>,	/* A2 */
			   <3 0 &gpio0 28 0>,	/* A3 */
			   <4 0 &gpio0 2 0>,	/* A4 */
			   <5 0 &gpio0 3 0>,	/* A5 */
			   <6 0 &gpio0 14 0>,	/* SCK */
			   <7 0 &gpio0 13 0>,	/* MOSI */
			   <8 0 &gpio0 15 0>,	/* MISO */
			   <9 0 &gpio0 24 0>,	/* RXD */
			   <10 0 &gpio0 25 0>,	/* TXD */
			   <11 0 &gpio0 10 0>,	/* D2 (NFC2) */
			   <12 0 &gpio0 12 0>,	/* SDA */
			   <13 0 &gpio0 11 0>,	/* SCL */
			   <14 0 &gpio1 8 0>,	/* D5 */
			   <15 0 &gpio0 7 0>,	/* D6 */
			   <16 0 &gpio0 26 0>,	/* D9 */
			   <17 0 &gpio0 27 0>,	/* D10 */
			   <18 0 &gpio0 6 0>,	/* D11 */
			   <19 0 &gpio0 8 0>,	/* D12 */
			   <20 0 &gpio1 9 0>;	/* D13 */
	};
};

feather_serial: &uart0 {};
feather_i2c: &i2c0 {};
feather_spi: &spi1 {};

So, I guess I need to figure out how to use the Zephyr DTS macros to get a device pointer for feather_header and from there the specific pin I want to use? I'll keep investigating but if anyone wants to make this easier for me, please don't hesitate :-)