i2c.c

/* 

Example I2C use on linux/raspberry pi

*/

#include <stdio.h>
#include <fcntl.h>
#include <linux/i2c.h>
#include <linux/i2c-dev.h>
#include <stdint.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdlib.h>

#include "i2c.h"

/*
 * Pinout config for this example
 *
 * LIS3DH SDA => Raspberry Pi GPIO 2 (Physical pin 3)
 * LIS3DH SCL => Raspberry Pi GPIO 3 (Physical pin 5)
 *
 */

#define I2C_DEVICE "/dev/i2c-1"
#define I2C_LIS3DH_ADDRESS 0x18 /* Can also be 0x19 */

static int fd;

int i2c_init(void) {
    fd = open(I2C_DEVICE, O_RDWR);
    if (fd < 0) {
        fprintf(stderr, "i2c_init(): could not open device: %s\n", I2C_DEVICE);
        return 1;
    }

    if (ioctl(fd, I2C_SLAVE, I2C_LIS3DH_ADDRESS) < 0) {
        fprintf(stderr, "i2c_init(): failed to acquire bus/talk to slave\n");
        close(fd);
        return 1;
    }

    return 0;
}

int i2c_read(uint8_t reg, uint8_t *dst, uint32_t size) {
    uint8_t cmd[2];

    if (size > 1) {
        reg |= 0x80; /* AUTO INC */
    }

    cmd[0] = reg;
    cmd[1] = 0x00;

    if (write(fd, cmd, 2) != 2) {
        fprintf(stderr, "i2c_read(): error write()\n");
        return 1;
    }
    
    if (read(fd, dst, size) != (int)size) {
        fprintf(stderr, "i2c_read(): error read()\n");
        return 1;
    
    }

    return 0;
}

int i2c_write(uint8_t reg, uint8_t value) {
    uint8_t cmd[2];

    cmd[0] = reg;
    cmd[1] = value;
    
    if (write(fd, cmd, 2) != 2) {
        fprintf(stderr, "i2c_write(): error write()\n");
        return 1;
    }

    return 0;
}

int i2c_deinit(void) {
    if (fd) {
        close(fd);
    }

    return 0;
}