c - Reading and writing EEPROM via I2C with Linux -


i trying read , write atmel 24c256 eeprom raspberry pi b+ on i2c, i'm having trouble getting work right.

here code have 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 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 %d bytes @ time.\n", page_size);      return -1;      }      int i;      my_buf[0] = addr_hi;      my_buf[1] = addr_lo;       for(i= 0; < 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 = 0;     while(i < page_size && *buf)     {     buffer[i+2] = *buf++;     }     while(i++ < page_size-1)     {     buffer[i+2] = '*'; // fill buffer     } }   int main() {      setupi2c(); //setup      fill_buffer("here 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 device in line write_to_device(0x01, 0x00, buffer, page_size); doesn't generate errors when try read device, have write "dummy" byte according spec sheet , try read device reason writing dummy byte results in error "input/output error". can't figure out how works. using 2 resources guide me, linux i2c-dev documentation , example similar eeprom device. i'm sort of stuck here , don't know try. suggestions or pointers appreciated!

alternatively, access via kernel at24.c driver, if you're able compile , install different kernel device tree raspberry pi.

the kernel device tree needs specify eeprom's type , address, , i²c bus it's connected to. i'm not sure raspberry pi, beaglebone black eeprom goes this:

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

for device you'd specify compatible = "at,24c256";

ensure kernel config specifies config_eeprom_at24=y (or =m).

then should able access eeprom memory userspace @ /sys/bus/i2c/devices/0-0050/eeprom or /sys/bus/i2c/drivers/at24/0-0050/eeprom.


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