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samples: application_development: introduce deinit
Introduce device deinit sample which demonstrates how to share hardware resources between application and device drivers using device_deinit(), specifically between a GPIO port and SPI peripheral. Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>
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‎samples/application_development/deinit/CMakeLists.txt‎

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# SPDX-License-Identifier: Apache-2.0
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(deinit)
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target_sources(app PRIVATE src/main.c)

‎samples/application_development/deinit/README.rst‎

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.. zephyr:code-sample:: deinit
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:name: Device deinit
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:relevant-api: gpio_interface spi_interface device_model
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Overview
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********
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This sample demonstrates how to initialize and deinitialize device
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drivers at runtime, which allows switching between different devices
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and device drivers which share pins or share hardware.
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Detailed description
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********************
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This sample demonstrates how to share a SPI CS (chip-select) pin
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between a SPI peripheral and a GPIO port. The SPI CS pin chosen is
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connected to an LED on the board used for the sample. This sample
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blinks the LED, by either manually toggling the pin using the GPIO
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port, or performing a mock SPI transaction with ``SPI_HOLD_ON_CS``
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set which keeps the SPI CS pin asserted from the start of the SPI
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transaction until we call :c:func:`spi_release`.
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We use ``zephyr,deferred-init`` to prevent initializing the SPI
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device driver during boot. The sample does the following after
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booting:
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1. Configure the CS pin as an output in active state with
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:c:func:`gpio_pin_configure_dt`
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2. Wait
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3. Configure the CS pin as an input with
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:c:func:`gpio_pin_configure_dt`
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This is the first blink
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4. Initialize the SPI device driver with :c:func:`device_init`
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5. Perform mock SPI transaction with :c:func:`spi_transceive`
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6. Wait
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7. Release SPI with :c:func:`spi_release`
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This is the second blink
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8. Deinitialize SPI device driver with :c:func:`device_deinit`
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9. Configure the CS pin as an output in active state with
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:c:func:`gpio_pin_configure_dt`
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10. Wait
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11. Configure the CS pin as an input
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:c:func:`gpio_pin_configure_dt`
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This is the third blink
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12. Initialize the SPI device driver with :c:func:`device_init`
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13. Perform mock SPI transaction with :c:func:`spi_transceive`
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14. Wait
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15. Release SPI with :c:func:`spi_release`
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This is the last blink.
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16. print ``sample complete`` to console
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If any errors occur during the sample, the error is printed to
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the console and the sample is stopped.
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Porting guide
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*************
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Use the following devicetree overlay example to create an
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overlay for your board:
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.. code-block:: devicetree
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&port0 {
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status = "okay";
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};
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&spi0 {
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status = "okay";
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zephyr,deferred-init;
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cs-gpios = <&port0 0 GPIO_ACTIVE_LOW>;
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};
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/ {
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zephyr,user {
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spi = <&spi0>;
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/*
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* Must match &spi0 cs-gpios and should
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* preferably be a pin connected to an LED
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* on the board, which illuminates when
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* active.
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*/
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cs-gpios = <&port0 0 GPIO_ACTIVE_LOW>;
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};
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};

‎samples/application_development/deinit/boards/frdm_ke15z.overlay‎

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/*
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* Copyright 2025 Nordic Semiconductor ASA
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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&pinctrl {
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lpuart0_default: lpuart0_default {
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group0 {
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pinmux = <LPSPI0_SCK_PTB2>,
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<LPSPI0_SIN_PTB3>,
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<LPSPI0_SOUT_PTB1>;
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bias-pull-up;
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drive-strength = "low";
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slew-rate = "slow";
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};
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};
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};
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&lpspi0 {
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pinctrl-0 = <&lpuart0_default>;
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pinctrl-names = "default";
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status = "okay";
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zephyr,deferred-init;
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cs-gpios = <&gpiod 0 GPIO_ACTIVE_LOW>;
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};
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&gpiod {
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status = "okay";
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};
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/ {
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zephyr,user {
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spi = <&lpspi0>;
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cs-gpios = <&gpiod 0 GPIO_ACTIVE_LOW>;
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};
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};

‎samples/application_development/deinit/boards/nrf5340dk_nrf5340_cpuapp.overlay‎

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/*
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* Copyright 2025 Nordic Semiconductor ASA
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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&spi4 {
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status = "okay";
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zephyr,deferred-init;
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cs-gpios = <&gpio0 30 GPIO_ACTIVE_LOW>;
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};
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/ {
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zephyr,user {
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spi = <&spi4>;
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cs-gpios = <&gpio0 30 GPIO_ACTIVE_LOW>;
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};
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};

‎samples/application_development/deinit/prj.conf‎

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CONFIG_SPI=y
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CONFIG_GPIO=y

‎samples/application_development/deinit/sample.yaml‎

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sample:
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name: Device deinit
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tests:
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sample.application_development.deinit:
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platform_allow:
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- nrf5340dk/nrf5340/cpuapp
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harness: console
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harness_config:
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type: one_line
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regex:
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- "sample complete"

‎samples/application_development/deinit/src/main.c‎

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/*
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* Copyright 2025 Nordic Semiconductor ASA
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <zephyr/kernel.h>
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#include <zephyr/device.h>
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#include <zephyr/drivers/spi.h>
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#include <zephyr/drivers/gpio.h>
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#define SPI_DEV_NODE DT_PROP(DT_PATH(zephyr_user), spi)
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static const struct device *const spi_dev = DEVICE_DT_GET(SPI_DEV_NODE);
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static const struct gpio_dt_spec cs_pin = GPIO_DT_SPEC_GET(DT_PATH(zephyr_user), cs_gpios);
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static uint8_t tx_buf[8];
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static const struct spi_buf tx_buf_pool[1] = {
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{
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.buf = tx_buf,
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.len = sizeof(tx_buf),
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},
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};
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static const struct spi_buf_set spi_tx_buf = {
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.buffers = tx_buf_pool,
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.count = ARRAY_SIZE(tx_buf_pool),
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};
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static const struct spi_config config = {
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.frequency = DT_PROP_OR(SPI_DEV_NODE, max_frequency, 1000000),
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.operation = SPI_OP_MODE_MASTER | SPI_HOLD_ON_CS | SPI_WORD_SET(8),
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.slave = 0,
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.cs = {
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.gpio = GPIO_DT_SPEC_GET_OR(SPI_DEV_NODE, cs_gpios, {0}),
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.delay = 0,
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},
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};
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static int control_cs_pin_with_gpio(void)
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{
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int ret;
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ret = gpio_pin_configure_dt(&cs_pin, GPIO_OUTPUT_ACTIVE);
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if (ret) {
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printk("failed to configure CS pin\n");
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return 0;
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}
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k_msleep(1000);
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ret = gpio_pin_configure_dt(&cs_pin, GPIO_INPUT);
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if (ret) {
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printk("failed to configure CS pin\n");
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return 0;
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}
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k_msleep(1000);
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return 0;
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}
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static int control_cs_pin_with_spi(void)
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{
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int ret;
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/*
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* Perform SPI transaction and keep CS pin asserted after
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* after transaction (see config.operation).
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*/
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ret = spi_transceive(spi_dev, &config, &spi_tx_buf, NULL);
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if (ret) {
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printk("failed to perform SPI transaction (ret %d)\n", ret);
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return 0;
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}
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k_msleep(1000);
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/* Release SPI device and thus CS pin shall be deasserted */
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ret = spi_release(spi_dev, &config);
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if (ret) {
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printk("failed to release SPI device (ret %d)\n", ret);
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return 0;
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}
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k_msleep(1000);
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return 0;
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}
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int main(void)
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{
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int ret;
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/*
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* As we have specified deferred init for the SPI device in the devicetree, the driver
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* will not be initialized at this stage. We should have full control of the CS GPIO,
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* let's test that.
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*/
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ret = control_cs_pin_with_gpio();
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if (ret) {
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printk("failed to control CS pin with GPIO device driver (ret %d)\n", ret);
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return 0;
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}
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/*
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* Now lets initialize the SPI device driver.
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*/
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ret = device_init(spi_dev);
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if (ret) {
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printk("failed to init SPI device driver (ret %d)\n", ret);
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return 0;
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}
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/*
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* To control the CS pin in "human speed", lets perform a mock
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* transaction, holding the CS pin until we release the SPI device.
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*/
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ret = control_cs_pin_with_spi();
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if (ret) {
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printk("failed to control CS pin with SPI device driver (ret %d)\n", ret);
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return 0;
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}
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/*
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* Lets deinit the SPI device driver an manually control the
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* CS pin again.
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*/
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ret = device_deinit(spi_dev);
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if (ret) {
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printk("failed to deinit SPI device driver (ret %d)\n", ret);
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return 0;
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}
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ret = control_cs_pin_with_gpio();
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if (ret) {
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printk("failed to control CS pin with GPIO device driver (ret %d)\n", ret);
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return 0;
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}
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/*
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* Lastly, lets check if we can bring back the SPI device driver.
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*/
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ret = device_init(spi_dev);
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if (ret) {
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printk("failed to init SPI device driver (ret %d)\n", ret);
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return 0;
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}
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/* One final blink */
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ret = control_cs_pin_with_spi();
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if (ret) {
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printk("failed to control CS pin with SPI device driver (ret %d)\n", ret);
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return 0;
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}
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printk("sample complete\n");
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return 0;
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}

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