Read and Write EEPROM via I2C with Linux

I am trying to read and write an Atmel 24C256 EEPROM using a Raspberry Pi B + versus I2C but I am having a hard time getting it all working right.

Here is the code I have so far:

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

#define DEVICE_PATH "/dev/i2c-1"

#define PAGE_SIZE 64

#define DEVICE_ADDR 0x50 // 0b1010xxxx


int file_desc;
char buffer[PAGE_SIZE + 2]; // 64 bytes + 2 for the address

void teardownI2C()
{
    int result = close(file_desc);
}

void setupI2C()
{
    file_desc = open(DEVICE_PATH, O_RDWR);
    if(file_desc < 0)
    {
    printf("%s\n", strerror(errno));
    exit(1);
    }
    if(ioctl(file_desc, I2C_SLAVE, DEVICE_ADDR) < 0)
    {
    printf("%s\n", strerror(errno));
    teardownI2C();
    exit(1);

    }
}

int write_to_device(char addr_hi, char addr_lo, char * buf, int len)
{
     struct i2c_rdwr_ioctl_data msg_rdwr;
     struct i2c_msg i2cmsg;
     char my_buf[PAGE_SIZE + 2];
     if(len > PAGE_SIZE + 2)
     {
     printf("Can't write more than %d bytes at a time.\n", PAGE_SIZE);
     return -1;
     }
     int i;
     my_buf[0] = addr_hi;
     my_buf[1] = addr_lo;

     for(i= 0; i < len; i++)
     {
     my_buf[2+i] = buf[i];
     }
     msg_rdwr.msgs = &i2cmsg;
     msg_rdwr.nmsgs = 1;
     i2cmsg.addr  = DEVICE_ADDR;
     i2cmsg.flags = 0;
     i2cmsg.len   = 2+len;
     i2cmsg.buf   = my_buf;

    if(ioctl(file_desc,I2C_RDWR,&msg_rdwr)<0)
    {
    printf("write_to_device(): %s\n", strerror(errno));
    return -1;
    }

    return 0;

}

int read_from_device(char addr_hi, char addr_lo, char * buf, int len)
{
    struct i2c_rdwr_ioctl_data msg_rdwr;
    struct i2c_msg             i2cmsg;



    if(write_to_device(addr_hi, addr_lo ,NULL,0)<0)
    {
    printf("read_from_device(): address reset did not work\n");
    return -1;
    }

    msg_rdwr.msgs = &i2cmsg;
    msg_rdwr.nmsgs = 1;

    i2cmsg.addr  = DEVICE_ADDR;
    i2cmsg.flags = I2C_M_RD;
    i2cmsg.len   = len;
    i2cmsg.buf   = buf;

    if(ioctl(file_desc,I2C_RDWR,&msg_rdwr)<0)
    {
    printf("read_from_device(): %s\n", strerror(errno));
    return -1;
    }


    return 0;
}

void fill_buffer(char *buf)
{
    int i = 0;
    while(i < PAGE_SIZE && *buf)
    {
    buffer[i+2] = *buf++;
    }
    while(i++ < PAGE_SIZE-1)
    {
    buffer[i+2] = '*'; // fill the buffer with something
    }
}


int main()
{

    setupI2C(); //setup

    fill_buffer("Here are some words.");
    write_to_device(0x01, 0x00, buffer, PAGE_SIZE);
    char newbuf[PAGE_SIZE];

    if(read_from_device(0x01, 0x00, newbuf, PAGE_SIZE)>0)
    {
    printf("%s\n", newbuf);
    }


    teardownI2C(); //cleanup
    return EXIT_SUCCESS;
}

      

Writing to the device as in a string write_to_device(0x01, 0x00, buffer, PAGE_SIZE);

does not throw any errors, but when I try to read from the device I have to write the "dummy" byte according to the spec and then try to read the device, but for whatever reason, writing the file bytes results in error "I / O error". I cannot figure out how it works. I am using two resources for the tutorial, Linux I2C-Dev Documentation and an example from a similar EEPROM device. I'm kind of stuck here and don't know what to try. Any suggestions or pointers are appreciated!

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4 answers


Alternatively, you can access it through a kernel driver at24.c

if you can compile and install a different kernel device tree for your Raspberry Pi.

In the kernel device tree, you must specify the type and address of the EEPROM and to which the I²C bus is connected. I'm not sure about the Raspberry Pi, but for the BeepleBone Black EEPROM, it looks like this:

&i2c0 {
    eeprom: eeprom@50 {
        compatible = "at,24c32";
        reg = <0x50>;
    };
};

      



For your device, you must specify compatible = "at,24c256";

Make sure the kernel config has CONFIG_EEPROM_AT24=y

(or =m

).

Then you should be able to access the EEPROM from user space with something like /sys/bus/i2c/devices/0-0050/eeprom

or /sys/bus/i2c/drivers/at24/0-0050/eeprom

.

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Maybe this can help. http://www.richud.com/wiki/Rasberry_Pi_I2C_EEPROM_Program as it apparently handles the device you are trying to program and also explains some caveats about 24c256 addressing



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My code:

enter code here

__s32 write_eeprom(__s32 fd,__u32 offset,__u32 len,__u8 *buf)
{
    __s32 ret;
    struct i2c_rdwr_ioctl_data msg_set;
    struct i2c_msg iomsgs;
    __u32 sended, sending;
    __u8 temp[ONE_PAGE + 1];

    if((offset + len) > BYTES_MAX || len == 0)
    {
        printf("write too long than BYTES_MAX\n");
        return -1;
    }
    sended = 0;
    iomsgs.addr = DEVICE_ADDR;
    iomsgs.flags = 0;   //write
    iomsgs.buf = temp;
    msg_set.msgs = &iomsgs;
    msg_set.nmsgs = 1;
    while(len > sended)
    {
        if(len - sended > ONE_PAGE)
            sending = ONE_PAGE;
        else
            sending = len - sended;
        iomsgs.len = sending + 1;
        temp[0] = offset + sended;
        memcpy(&temp[1], buf + sended, sending);
        //printf("sending:%d sended:%d len:%d offset:%d \n", sending, sended, len, offset);
        ret = ioctl(fd, I2C_RDWR, (unsigned long)&msg_set);
        if(ret < 0)
        {
            printf("Error dring I2C_RDWR ioctl with error code: %d\n", ret);
            return ret;
        }
        sended += sending;
        usleep(5000);
    }

    return sended;
}

      

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Small and simple program to understand simple eeprom management

/*
    Simple program to write / read the eeprom AT24C32.
    Developed and tested on the Raspberry pi3B jessie

    To create the executable use the following command:

        gcc -Wall -o thisprogram.exe thisprogram.c
*/

#include <stdio.h>
#include <sys/ioctl.h> // ioctl
#include <fcntl.h>     // open
#include <unistd.h>    // read/write usleep
#include <time.h>
#include <netinet/in.h> // htons
#include <linux/i2c-dev.h>

#pragma pack(1)

#define PAGESIZE 32
#define NPAGES  128
#define NBYTES (NPAGES*PAGESIZE)

#define ADDRESS 0x57  //  AT24C32 address on I2C bus 

typedef struct {
    ushort AW;
    char  buf[PAGESIZE+2];
}WRITE;

static WRITE AT = {0};

int main() {
  int fd;
  char bufIN[180] = {0};
  time_t clock=time(NULL);

  snprintf(AT.buf, PAGESIZE+1, "%s: my first attempt to write", ctime(&clock)); //  the buffer to write, cut to 32 bytes

  if ((fd = open("/dev/i2c-1", O_RDWR)) < 0) {  printf("Couldn't open device! %d\n", fd); return 1; }

  if (ioctl(fd, I2C_SLAVE, ADDRESS) < 0)     { printf("Couldn't find device on address!\n"); return 1; }

  AT.AW = htons(32);    //  I will write to start from byte 0 of page 1 ( 32nd byte of eeprom )

  if (write(fd, &AT, PAGESIZE+2) != (PAGESIZE+2)) { perror("Write error !");    return 1; }
  while (1) { char ap[4];  if (read(fd,&ap,1) != 1) usleep(500); else break; } //   wait on write end 

  if (write(fd, &AT, 2) != 2) {  perror("Error in sending the reading address");    return 1;  }

  if (read(fd,bufIN,PAGESIZE) != PAGESIZE) { perror("reading error\n"); return 1;}
  printf ("\n%s\n", bufIN);

  close(fd);
  return 0;
}

      

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