Reading a 32k i2c eeprom from userland - c

Question

I need to read an eeprom in an embedded device.
So far this "almost" worked:
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>
#define READ_SIZE (256)
#define NB_PAGES (128)
void dump_to_file(const char *output_file_path,
const uint8_t *buffer, const int buffer_length)
{
int output_file = open(output_file_path, O_RDWR|O_APPEND|O_CREAT);
if (output_file < 0) {
printf("Failed opening output file %s\n", output_file_path);
return;
}
write(output_file, buffer, buffer_length);
}
int main(int argc, char *argv[])
{
/* got these values from i2cdetect */
const char *i2c_device = "/dev/i2c-4";
const int device_address = 0x50;
/* open the i2c device file */
int file = open(i2c_device, O_RDWR);
if (file < 0) {
printf("Failed opening %s\n", i2c_device);
return 1;
}
if (ioctl(file, I2C_SLAVE, device_address) < 0) {
printf("Failed addressing device at %02X\n", device_address);
close(file);
return 1;
}
int i = 0;
for (i = 0; i < NB_PAGES; i++) {
char buf[READ_SIZE] = {0};
if (read(file, buf, READ_SIZE) != READ_SIZE) {
printf("Failed reading\n");
close(file);
return 1;
}
dump_to_file(argv[1], buf, READ_SIZE);
}
close(file);
return 0;
}
By "almost" I mean that it dumps the full eeprom but the START depends on the last block read..
It's not always the same.
If I read 10 blocks. then run the program again I read the next ones and not the first 10.
How to set the starting address?
Update:
if I do:
i2cset -y 4 0x50 0x00 0x00
and the run the above code, it works.
so how can I put the equivalent of the i2cset command in the code?

Answer 1

Done!
It wasn't easy because I could not find documentations anywhere.. but I thought that since the eeprom is 32K, maybe it was "like" a 24c256. But even in that case I found nothing in userspace until I decided to go by instinct.
I studied i2cset source, understood what it did and put it in the code.
Here is the result, which dumps a full i2c 32k eprom from userspace.
Note a full backup and restore utility can be found here:
https://gist.github.com/Zibri/cf8ac0b311301aeeaa8910c7da824bff
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/i2c-dev.h>
#define READ_SIZE (256)
#define NB_PAGES (128)
void dump_to_file(const char *output_file_path,
const uint8_t *buffer, const int buffer_length)
{
int output_file = open(output_file_path, O_RDWR|O_APPEND|O_CREAT);
if (output_file < 0) {
printf("Failed opening output file %s\n", output_file_path);
return;
}
write(output_file, buffer, buffer_length);
}
int main(int argc, char *argv[])
{
const char *i2c_device = "/dev/i2c-4";
const int device_address = 0x50;
int file = open(i2c_device, O_RDWR);
if (file < 0) {
printf("Failed opening %s\n", i2c_device);
return 1;
}
if (ioctl(file, I2C_SLAVE, device_address) < 0) {
printf("Failed addressing device at %02X\n", device_address);
close(file);
return 1;
}
int i = 0;
write(file,'\x00\x00',2); // ADDRESS
for (i = 0; i < NB_PAGES; i++) {
char buf[READ_SIZE] = {0};
if (read(file, buf, READ_SIZE) != READ_SIZE) {
printf("Failed reading\n");
close(file);
return 1;
}
dump_to_file(argv[1], buf, READ_SIZE);
}
close(file);
return 0;
}