Raspberry Pi example for I2C operations

rpi_i2c.c

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

#include "i2c.h"

/* Init I2Cdevice */
int i2c_init( char fdname[40], int addr )
{
    int fd = open(fdname, O_RDWR);
    
    if( fd < 0 )
    {
        printf("Failed to open the bus\r\n\r");
        return fd;
    }
    
    printf("Open i2c \"%s\"...\r\n\r", fdname);
    

    if( ioctl(fd, addr) < 0 )
    {
        printf("Failed to acquire bus access and/or talk to slave for address %x\r\n\r", addr_error);
        return fd;
    }

    printf("I2C address init...\r\n\r");
    return fd;
}

/* Read n bytes */
int i2c_read(int fd, int add1, int add2, int nbytes, unsigned char *buf)
{
    int n;
    
#ifdef DEBUG
    
    printf("Reading %d bytes...\r\n\r", nbytes);
    
#endif
    
    if( read(fd, buf, nbytes) != nbytes )
    {
        fprintf(stderr, "Error reading %i bytes\r\n\r", nbytes);
    }
    else
    {
        
#ifdef DEBUG
	
        printf("[ OK ] | ");		
        for (n = 0; n < nbytes; n++)
        {
            printf("r_0x%0*x ", 2, *buf++);
        }
        printf("\r\n\r");
        
#endif
    }
    return nbytes;
}

/* Write n bytes */
void i2c_write(int fd, int add1, int add2, int nbytes, unsigned char value[2])
{
    int n, i;
    unsigned char buf[10];
    buf[0] = add1;
    buf[1] = add2;

    if (nbytes >= 1)
    {
        buf[2] = value[0];
    }
    if (nbytes >= 2)
    {
        buf[3] = value[1];
    }
    if (nbytes >= 3)
    {
        buf[4] = value[2];
    }
    if (nbytes >= 4)
    {
        buf[5] = value[3];
    }
    
#ifdef DEBUG
    
    printf("Write (address | data): %02X%02X | ", buf[0], buf[1]);
    for (i = 0; i < nbytes; i++)
    {
        printf("%02X ", buf[i+2]);
    }
    printf("\r\n\r");
    
#endif	

    if( write(fd, buf, nbytes+2) != nbytes+2 )
    {
        printf("Error writing %i bytes\r\n\r", nbytes);
    }
#ifdef DEBUG
    else
    {
        printf("Write done succesfully\r\n\r");
    }
#endif
}

rpi_i2c.h

#ifndef RPI_I2C_H
#define RPI_I2C_H

#ifdef __cplusplus
extern "C" {
#endif

/* Init I2Cdevice */
int i2c_init(char filename[40], int addr);

/* Read n bytes */
int i2c_read(int fd, int add1, int add2, int nbytes, unsigned char *buf);

/* Write n bytes */
void i2c_write(int fd, int add1, int add2, int nbytes, unsigned char *buf);

#ifdef __cplusplus
}
#endif

#endif /* RPI_I2C_H */