I2cread.c

/* a simple program to read on i2c bus
 * Fabien Marteau <fabien.marteau@armadeus.com>
 *
 * inspired from : 
 *   ch7024: manage the Svideo controller CH7024
 *  author: thom25@users.sourceforge.net
 *
 *
 **  THE ARMADEUS PROJECT
 **
 **  Copyright (C) year  The source forge armadeus project team
 **
 ** This program is free software; you can redistribute it and/or modify
 ** it under the terms of the GNU General Public License as published by
 ** the Free Software Foundation; either version 2 of the License, or
 ** (at your option) any later version.
 ** 
 ** This program is distributed in the hope that it will be useful,
 ** but WITHOUT ANY WARRANTY; without even the implied warranty of
 ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 ** GNU General Public License for more details.
 ** 
 ** You should have received a copy of the GNU General Public License
 ** along with this program; if not, write to the Free Software 
 ** Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 **
 */
#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;

/* Read a byte on the I2C bus
   This is done by writing the register address 
   we want to access and then by reading this register
     @param fd: file descriptor of the device
     @param reg: register to access
     @param buf: buffer used to store the result
     @return : -1 in case of error otherwise 0
 */
int read_byte( int fd,unsigned char addr, unsigned char reg, unsigned char *buf )
{ 
    // create an I2C write message (only one byte: the address)
    struct i2c_msg msg = {addr, 0, 1, buf };
    // create a I2C IOCTL request
    struct i2c_rdwr_ioctl_data rdwr = { &msg, 1 };

    buf[0] = reg; // select reg to read

    // write the desired register address
	if ( ioctl( fd, I2C_RDWR, &rdwr ) < 0 ){
		printf("Write error\n");
		return -1;
	}
    msg.flags = I2C_M_RD; // read
    
    // read the result and write it in buf[0]
	if ( ioctl( fd, I2C_RDWR, &rdwr ) < 0 ){
		printf("Read error\n");
		return -1;
	}
    return 0;
}

/* i2cread i2c-devfile addr*/
int main(int argc, char **argv){
  unsigned char buf;
  unsigned char addr;
  unsigned char subaddr;
  unsigned char value;

  if(argc != 4){
    printf("wrong args numbers\nsyntaxe (hexa) :\ni2cread i2c-devfile addr subaddr\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);

  read_byte(fd,addr, subaddr, &buf); 

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

  return value;
}