Accessing I2C devices from userspace in Linux

				
					#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/i2c-dev.h>
    
#define I2C_DEVICE      "/dev/i2c-0"
#define I2C_ADDR        0x53    // Device address
#define REG_POWER_CTL   0x2D    // Power control register
#define REG_DATA_START  0x32    // Data register start

int main(void) {
    int file;
    uint8_t buf[2];
    uint8_t data[6];
    int16_t x, y, z;

    // Open I2C device
    if ((file = open(I2C_DEVICE, O_RDWR)) < 0) {
        perror("Failed to open the i2c bus");
        exit(EXIT_FAILURE);
    }
    
    // Specify the address of the I2C Device to communicate with
    if (ioctl(file, I2C_SLAVE, I2C_ADDR) < 0) {
        perror("Failed to acquire bus access and/or talk to device");
        close(file);
        exit(EXIT_FAILURE);
    }
    
    // Wake up the device: write 0x08 to POWER_CTL register
    buf[0] = REG_POWER_CTL;
    buf[1] = 0x08;
    if (write(file, buf, 2) != 2) {
        perror("Failed to write to the power control register");
        close(file);
        exit(EXIT_FAILURE);
    }
    
    printf("Reading 6 bytes from register 0x%02X...\n", REG_DATA_START);
    // Set register pointer to data start
    buf[0] = REG_DATA_START;
    if (write(file, buf, 1) != 1) {
        perror("Failed to set data register pointer");
        break;
    }
    
    // Read 6 bytes of data (X, Y, Z)
    if (read(file, data, 6) != 6) {
        perror("Failed to read data from device");
        break;
    }
    
    // Convert little-endian bytes to signed 16-bit values
    x = (int16_t)((data[1] << 8) | data[0]);
    y = (int16_t)((data[3] << 8) | data[2]);
    z = (int16_t)((data[5] << 8) | data[4]);
    // Print the raw values
    printf("X: %6d, Y: %6d, Z: %6d\n", x, y, z);
    close(file);
    return 0;
}