Hi,

I plan to use the accelerometer to control some servos on an helicopter
But it is written on the wiki  that the accelerometter is on i2C. Maybe my firmware is not up to date. I'll check that tonight, I dont have an internet connection right now on the board.

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

// The 'raw' 7 bit address shifted up
#define MMA7455_I2CADDR (0x1D * 2)

// The registers to read!
#define MMA7455_XOUT8 6
#define MMA7455_YOUT8 7
#define MMA7455_ZOUT8 8

#define I2C_FILE_NAME "/dev/i2c-0"

static int get_i2c_register(int file,
                            unsigned char addr,
                            unsigned char reg,
                            unsigned char *val) {
    unsigned char inbuf, outbuf;
    struct i2c_rdwr_ioctl_data packets;
    struct i2c_msg messages[2];

    /*
     * In order to read a register, we first do a "dummy write" by writing
     * 0 bytes to the register we want to read from.  This is similar to
     * the packet in set_i2c_register, except it's 1 byte rather than 2.
     */
    outbuf = reg;
    messages[0].addr  = addr;
    messages[0].flags = 0;
    messages[0].len   = sizeof(outbuf);
    messages[0].buf   = &outbuf;

    /* The data will get returned in this structure */
    messages[1].addr  = addr;
    messages[1].flags = I2C_M_RD/* | I2C_M_NOSTART*/;
    messages[1].len   = sizeof(inbuf);
    messages[1].buf   = &inbuf;

    /* Send the request to the kernel and get the result back */
    packets.msgs      = messages;
    packets.nmsgs     = 2;
    if(ioctl(file, I2C_RDWR, &packets) < 0) {
        perror("Unable to send data");
        return 1;
    }
    *val = inbuf;

    return 0;
}

int main(int argc, char **argv) {
    int i2c_file;
    int8_t x, y, z;  // the readings are 8 bits and signed!

    // Open a connection to the I2C userspace control file.
    if ((i2c_file = open(I2C_FILE_NAME, O_RDWR)) < 0) {
        perror("Unable to open i2c control file");
        exit(1);
    }

    // ignore arguments!

    while (1) {
     
      // read X and Y and Z from the register
      if( get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_XOUT8, &x) ||
      get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_YOUT8, &y) ||
      get_i2c_register(i2c_file, MMA7455_I2CADDR, MMA7455_ZOUT8, &z) ) {

    printf("Unable to read register!\n");
    return -1;
      }

      printf("X = %d\tY = %d\tZ = %d\n", x, y, z);
    }

    close(i2c_file);
    return 0;
}

I try to use this program: