I2cwrite.c

/* a simple program to write on i2c bus*
 * Fabien Marteau <fabien.marteau@armadeus.com>
 *
 * Inspired from another code, but I don't remember who.
 */


#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

#include <linux/i2c.h> 
#include <linux/i2c-dev.h>
 
#include <sys/ioctl.h>

int fd;

/* Write a byte on the I2C bus
     @param fd: file descriptor of the device
     @param reg: register to access
     @param value: value to write
     @return : -1 in case of error otherwise 0   
 */
int write_byte(int fd,unsigned char addr, unsigned char reg, unsigned char value)
{
    unsigned char buf[2] = {reg,value}; // initialise a data buffer with 
                                        // address and data

    // create an I2C write message
    struct i2c_msg msg = {addr, 0, sizeof(buf), buf };
    // create a I2C IOCTL request
    struct i2c_rdwr_ioctl_data rdwr = { &msg, 1 };

#ifdef DEBUG_CH7024
    printf("write ref %02X value %02X\n",reg, value);
#endif
	if ( ioctl( fd, I2C_RDWR, &rdwr ) < 0 ){
		printf("Write error\n");
		return -1;
	}
    return 0;
}

/* i2cwrite i2c-devfile addr value*/
int main(int argc, char **argv){
  unsigned char buf;
  unsigned char addr;
  unsigned char subaddr;
  unsigned char value;

  if(argc != 5){
    printf("wrong args numbers\nsyntaxe (value in hexa) :\ni2cwrite i2c-devfile addr subaddr value\n");
    return -1;
  }

  fd = open(argv[1],O_RDWR);
  if(fd < 0){
    printf("can't open %s\n",argv[1]);
    return -1;
  }
  addr    =    (unsigned char )strtol(argv[2], (char **)NULL, 16);
  subaddr =    (unsigned char )strtol(argv[3], (char **)NULL, 16);
  buf =    (unsigned char )strtol(argv[4], (char **)NULL, 16);


  write_byte(fd,addr, subaddr, buf); 

  printf("Wrote component %02x at subaddress %02x -> %02x\n",addr,subaddr,buf);

  return value;
}