Zephyr Gpio

Zephyr GPIO Skill

Overview

This skill provides guidance for implementing GPIO functionality in Zephyr RTOS applications. GPIO (General Purpose Input/Output) is fundamental to embedded systems for controlling LEDs, reading buttons, and interfacing with digital peripherals.

API Selection Decision Tree

Need GPIO?
├── Single pin from devicetree?
│   └── Use gpio_dt_spec + _dt() functions (RECOMMENDED)
│       └── GPIO_DT_SPEC_GET(node, prop) → gpio_pin_configure_dt() → gpio_pin_set_dt()/gpio_pin_get_dt()
│
├── Multiple pins, same port?
│   └── Use gpio_port_*() functions for efficiency
│       └── gpio_port_set_masked() / gpio_port_get()
│
└── Runtime-determined pin?
    └── Use raw API with device + pin number
        └── DEVICE_DT_GET() → gpio_pin_configure() → gpio_pin_set()/gpio_pin_get()

Getting Device Reference

From Devicetree (Preferred)

/* For nodes with gpios property (e.g., gpio-leds, gpio-keys) */
#define LED_NODE DT_ALIAS(led0)
static const struct gpio_dt_spec led = GPIO_DT_SPEC_GET(LED_NODE, gpios);

/* Check device readiness before use */
if (!gpio_is_ready_dt(&led)) {
    return -ENODEV;
}

gpio_dt_spec Structure

struct gpio_dt_spec {
    const struct device *port;  /* GPIO controller device */
    gpio_pin_t pin;             /* Pin number (0-31 typically) */
    gpio_dt_flags_t dt_flags;   /* Flags from devicetree (e.g., GPIO_ACTIVE_LOW) */
};

Common Workflows

1. Basic LED Blinky

#include <zephyr/kernel.h>
#include <zephyr/drivers/gpio.h>

#define LED_NODE DT_ALIAS(led0)
static const struct gpio_dt_spec led = GPIO_DT_SPEC_GET(LED_NODE, gpios);

int main(void)
{
    if (!gpio_is_ready_dt(&led)) {
        return -ENODEV;
    }

    int ret = gpio_pin_configure_dt(&led, GPIO_OUTPUT_ACTIVE);
    if (ret < 0) {
        return ret;
    }

    while (1) {
        gpio_pin_toggle_dt(&led);
        k_msleep(1000);
    }
    return 0;
}

2. Button Input (Polled)

#define BUTTON_NODE DT_ALIAS(sw0)
static const struct gpio_dt_spec button = GPIO_DT_SPEC_GET(BUTTON_NODE, gpios);

int main(void)
{
    if (!gpio_is_ready_dt(&button)) {
        return -ENODEV;
    }

    gpio_pin_configure_dt(&button, GPIO_INPUT);

    while (1) {
        int val = gpio_pin_get_dt(&button);
        if (val > 0) {
            /* Button pressed (handles ACTIVE_LOW automatically) */
        }
        k_msleep(100);
    }
}

3. Button with Interrupt

static const struct gpio_dt_spec button = GPIO_DT_SPEC_GET(DT_ALIAS(sw0), gpios);
static struct gpio_callback button_cb_data;

void button_pressed(const struct device *dev, struct gpio_callback *cb, uint32_t pins)
{
    /* ISR context - keep short, use k_work for heavy processing */
    printk("Button pressed at %" PRIu32 "\n", k_cycle_get_32());
}

int main(void)
{
    if (!gpio_is_ready_dt(&button)) {
        return -ENODEV;
    }

    gpio_pin_configure_dt(&button, GPIO_INPUT);
    gpio_pin_interrupt_configure_dt(&button, GPIO_INT_EDGE_TO_ACTIVE);

    gpio_init_callback(&button_cb_data, button_pressed, BIT(button.pin));
    gpio_add_callback(button.port, &button_cb_data);

    /* Main loop or other work */
    while (1) {
        k_msleep(1000);
    }
}

4. Multiple Pins Configuration

/* Define multiple GPIO specs */
static const struct gpio_dt_spec leds[] = {
    GPIO_DT_SPEC_GET(DT_ALIAS(led0), gpios),
    GPIO_DT_SPEC_GET(DT_ALIAS(led1), gpios),
    GPIO_DT_SPEC_GET(DT_ALIAS(led2), gpios),
};

int init_leds(void)
{
    for (int i = 0; i < ARRAY_SIZE(leds); i++) {
        if (!gpio_is_ready_dt(&leds[i])) {
            return -ENODEV;
        }
        int ret = gpio_pin_configure_dt(&leds[i], GPIO_OUTPUT_INACTIVE);
        if (ret < 0) {
            return ret;
        }
    }
    return 0;
}

5. Bidirectional Pin (Input/Output switching)

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

void send_data(uint8_t bit)
{
    gpio_pin_configure_dt(&data_pin, GPIO_OUTPUT);
    gpio_pin_set_dt(&data_pin, bit);
}

int read_data(void)
{
    gpio_pin_configure_dt(&data_pin, GPIO_INPUT);
    return gpio_pin_get_dt(&data_pin);
}

Configuration

Essential Kconfig

CONFIG_GPIO=y                    # Enable GPIO driver subsystem (required)
# CONFIG_GPIO_LOG_LEVEL_DBG=y    # Enable for debugging

Devicetree Examples

LED definition:

/ {
    aliases {
        led0 = &green_led;
    };

    leds {
        compatible = "gpio-leds";
        green_led: led_0 {
            gpios = <&gpio0 13 GPIO_ACTIVE_LOW>;
            label = "Green LED";
        };
    };
};

Button definition:

/ {
    aliases {
        sw0 = &user_button;
    };

    buttons {
        compatible = "gpio-keys";
        user_button: button_0 {
            gpios = <&gpio0 11 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
            label = "User Button";
        };
    };
};

Generic GPIO:

/ {
    my_gpios {
        compatible = "gpio-leds";  /* Reuse for any GPIO */
        data_gpio: data {
            gpios = <&gpio0 5 GPIO_ACTIVE_HIGH>;
        };
    };
};

GPIO Flags Reference

Interrupt Flags

Interrupt Handling Pattern

With Work Queue (Recommended for complex handling)

static struct k_work button_work;
static const struct gpio_dt_spec button = GPIO_DT_SPEC_GET(DT_ALIAS(sw0), gpios);

void button_work_handler(struct k_work *work)
{
    /* Safe to do complex operations here */
    printk("Button handled in work queue\n");
}

void button_isr(const struct device *dev, struct gpio_callback *cb, uint32_t pins)
{
    k_work_submit(&button_work);
}

int main(void)
{
    k_work_init(&button_work, button_work_handler);

    gpio_pin_configure_dt(&button, GPIO_INPUT);
    gpio_pin_interrupt_configure_dt(&button, GPIO_INT_EDGE_TO_ACTIVE);

    static struct gpio_callback cb;
    gpio_init_callback(&cb, button_isr, BIT(button.pin));
    gpio_add_callback(button.port, &cb);

    return 0;
}

Debouncing with Delayed Work

static struct k_work_delayable debounce_work;
#define DEBOUNCE_MS 50

void debounce_handler(struct k_work *work)
{
    int val = gpio_pin_get_dt(&button);
    if (val > 0) {
        /* Confirmed button press */
    }
}

void button_isr(const struct device *dev, struct gpio_callback *cb, uint32_t pins)
{
    k_work_reschedule(&debounce_work, K_MSEC(DEBOUNCE_MS));
}

Error Handling

All GPIO functions return negative errno on failure:

int ret = gpio_pin_configure_dt(&led, GPIO_OUTPUT_ACTIVE);
if (ret < 0) {
    LOG_ERR("Failed to configure GPIO: %d", ret);
    return ret;
}

Common errors:

• -ENODEV: Device not ready or not found
• -ENOTSUP: Configuration not supported by hardware
• -EINVAL: Invalid pin number or flags

Troubleshooting

References

• references/api.md - Complete GPIO API function reference
• references/devicetree.md - Devicetree bindings and properties
• references/kconfig.md - All GPIO Kconfig options