I2C EEPROM Read/Write Cubieboard 2 Arch Linux - linux

Question

I am trying to read and write to the AT24MAC402 EEPROM over i2c on the Cubieboard 2 using Arch Linux. I am using the i2c-dev library and i2c-tools.
Datasheet:
http://www.atmel.com/images/atmel-8807-seeprom-at24mac402-602-datasheet.pdf
I can successfully write (kind of...) to a chosen address and sequentially write many bites starting at that address. The issues are:
Cannot re-select another address to write once the first address has been selected.
Cannot point the the EEPROM to the location I wish to read from (by dummy-writing), and therefore have almost no real control over the EEPROM.
Upon looking at the datasheet (for hours on end), it looks as if I don't have as much control over the I2C communications as I may need using the i2c-dev library.. It would be great if I could just write X bits or X bytes directly to the EEPROM.
In short, I would like advice on how I can read and write properly to this EEPROM.
char buf[10];
int com_serial;
int failcount;
int i2c_init(char filename[40], int addr)
{
int file;
if ((file = open(filename,O_RDWR)) < 0)
{
printf("Failed to open the bus.");
/* ERROR HANDLING; you can check errno to see what went wrong */
com_serial=0;
exit(1);
}
if (ioctl(file,I2C_SLAVE,addr) < 0)
{
printf("Failed to acquire bus access and/or talk to slave.\n");
/* ERROR HANDLING; you can check errno to see what went wrong */
com_serial=0;
exit(1);
}
return file;
}
int main (int argc, char *argv[]) {
char read_buf[16];
char write_buf[17];
int i;
int file;
file=i2c_init("/dev/i2c-1",0x50); //dev,slavei2caddr
write_buf[0] = 0x00;
write_buf[1] = 'H';
write_buf[2] = 'i';
write_buf[3] = '!';
write(file, write_buf, 4);
//Successfully prints "Hi!" to bytes 0x00 -> 0x02
//Setting EEPROM to point to address 0xA0 to start reading (arbitrary address with known values: all 0xFF)
write_buf[0] = 0xA0;
write(file, write_buf, 1);
//Reading 1 byte from EEPROM, even though there is a '2'; 2 bytes would be '3'
read(file, read_buf, 2);
for (i=1; i<3; i++){
printf("%X", read_buf[i]);
}
//Prints out from address 0x04 to 0x05 instead of 0xA0 to 0xA1
printf("\n");
}

Answer 1

I did work properly using the functions from the linux/i2c-dev.h.
To test the code I get the output generated by i2cdump and put as input to i2c-stub-from-dump tool, it lets you setup one or more fake I2C chips on the i2c-stub bus based on dumps of the chips you want to emulate.
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/i2c-dev.h>
int i2c_init(const char * i2c_device, const int chip_address)
{
int file;
if ((file = open(i2c_device, O_RDWR)) < 0) {
return -1;
}
if (ioctl(file, I2C_SLAVE, chip_address) < 0) {
close(file);
return -1;
}
return file;
}
int i2c_write(int file, const int data_address, const unsigned char * data, size_t size)
{
return i2c_smbus_write_i2c_block_data(file, data_address, size, data);
}
void i2c_read(int file, const int data_address, unsigned char * data_vector, size_t size)
{
unsigned char reg = data_address;
unsigned int i;
for(i = 0; i < size; ++i, ++reg) {
data_vector[i] = i2c_smbus_read_byte_data(file, reg);
}
}
int main(void) {
char device[] = "/dev/i2c-6";
int address = 0x50;
unsigned char buffer_before[30] = {0};
unsigned char buffer_after[30] = {0};
unsigned char data[] = "Hello World!";
int file;
file = i2c_init(device, address);
if (file > 0) {
i2c_read(file, 0x00, buffer_before, sizeof(data));
i2c_write(file, 0x00, data, sizeof(data));
i2c_read(file, 0x00, buffer_after, sizeof(data));
close (file);
}
printf("data read before write: %s\n", buffer_before);
printf("data read after write: %s\n", buffer_after);
return 0;
}