# C/C++ GPIO development

***Copyright © Quectel Wireless Solutions Co., Ltd. 2026. All rights reserved.***

---

This document describes the recommended method for accessing GPIO using C/C++ on the Quectel Pi M2. The current development board has been verified to support libgpiod v1.6.3, and the libgpiod approach is recommended by default.

# Environment Setup

```bash
sudo apt update
sudo apt install -y build-essential gpiod libgpiod-dev
gpiodetect --version
gpiodetect
```

| **Item** | **Description** |
| --- | --- |
| Recommended Library | libgpiod |
| Compilation Option | `-lgpiod` |
| Main Controller | Currently verified as `/dev/gpiochip0` |

# Input Example

```c
#include <gpiod.h>
#include <stdio.h>

int main(void)
{
    struct gpiod_chip *chip;
    struct gpiod_line_settings *settings;
    struct gpiod_line_config *line_cfg;
    struct gpiod_request_config *req_cfg;
    struct gpiod_line_request *request;
    unsigned int offset = 36;
    int value;

    chip = gpiod_chip_open("/dev/gpiochip0");
    if (!chip) {
        perror("gpiod_chip_open");
        return 1;
    }

    settings = gpiod_line_settings_new();
    gpiod_line_settings_set_direction(settings, GPIOD_LINE_DIRECTION_INPUT);

    line_cfg = gpiod_line_config_new();
    gpiod_line_config_add_line_settings(line_cfg, &offset, 1, settings);

    req_cfg = gpiod_request_config_new();
    gpiod_request_config_set_consumer(req_cfg, "m1-gpio-input");

    request = gpiod_chip_request_lines(chip, req_cfg, line_cfg);
    if (!request) {
        perror("gpiod_chip_request_lines");
        return 1;
    }

    value = gpiod_line_request_get_value(request, offset);
    printf("value=%d\n", value);

    gpiod_line_request_release(request);
    gpiod_line_config_free(line_cfg);
    gpiod_line_settings_free(settings);
    gpiod_request_config_free(req_cfg);
    gpiod_chip_close(chip);
    return 0;
}
```

```bash
gcc -Wall -o gpio_input gpio_input.c -lgpiod
sudo ./gpio_input
```

# Output Example

```c
#include <gpiod.h>
#include <stdio.h>
#include <unistd.h>

int main(void)
{
    struct gpiod_chip *chip;
    struct gpiod_line_settings *settings;
    struct gpiod_line_config *line_cfg;
    struct gpiod_request_config *req_cfg;
    struct gpiod_line_request *request;
    unsigned int offset = 36;

    chip = gpiod_chip_open("/dev/gpiochip0");
    if (!chip) {
        perror("gpiod_chip_open");
        return 1;
    }

    settings = gpiod_line_settings_new();
    gpiod_line_settings_set_direction(settings, GPIOD_LINE_DIRECTION_OUTPUT);
    gpiod_line_settings_set_output_value(settings, GPIOD_LINE_VALUE_ACTIVE);

    line_cfg = gpiod_line_config_new();
    gpiod_line_config_add_line_settings(line_cfg, &offset, 1, settings);

    req_cfg = gpiod_request_config_new();
    gpiod_request_config_set_consumer(req_cfg, "m1-gpio-output");

    request = gpiod_chip_request_lines(chip, req_cfg, line_cfg);
    if (!request) {
        perror("gpiod_chip_request_lines");
        return 1;
    }

    sleep(1);
    gpiod_line_request_set_value(request, offset, GPIOD_LINE_VALUE_INACTIVE);

    gpiod_line_request_release(request);
    gpiod_line_config_free(line_cfg);
    gpiod_line_settings_free(settings);
    gpiod_request_config_free(req_cfg);
    gpiod_chip_close(chip);
    return 0;
}
```

```bash
gcc -Wall -o gpio_output gpio_output.c -lgpiod
sudo ./gpio_output
```

# Notes

- The actual line offset must be confirmed against the development board's pin definitions.

- If execution fails, first use `gpioinfo /dev/gpiochip0` to check whether the line is in use.

- If the compiler reports that `gpiod.h` cannot be found, confirm that `libgpiod-dev` is installed.