> ## Documentation Index
> Fetch the complete documentation index at: https://docs.t3gemstone.org/llms.txt
> Use this file to discover all available pages before exploring further.

# EEPROM

> Electrically Erasable Programmable Read-Only Memory

<Tip>
  By the end of this section, you will gain experience in the following topics:

  * Technical specifications and usage examples of the EEPROM available in Gemstone
</Tip>

EEPROMs are generally used to store hardware or software parameters that can be configured on the board,
board-specific information (product type, serial number, etc.), or firmware (BIOS, etc.) because they do
not contain a file system, provide fast access during boot, and can retain stored data for a very long time
without corruption.

<Note>
  While SD Cards and USB Flash drives can store data for up to 10 years without corruption, the AT24C512C
  model EEPROM can retain data for 40 years without corruption.
</Note>

## EEPROM Usage

The board includes a 512-Kbit (64KiB) AT24C512C model EEPROM connected to the SoC via the I2C bus.
The necessary drivers for Linux are pre-installed, and it is defined in the [Device Tree](/en/faq#what-is-device-tree)
as follows:

```c++ lines theme={"system"}
&wkup_i2c0 {
	eeprom@51 {
		compatible = "atmel,24c512";
		reg = <0x51>;
	};
}
```

After connecting to the board's terminal, the following command should display a folder named `2-0051`:

```bash highlight=5 theme={"system"}
gemstone@t3-gem-o1:~$ ls /sys/bus/i2c/drivers/at24/
total 0
drwxr-xr-x  2 root root    0 Apr  7  2022 ./
drwxr-xr-x 66 root root    0 Apr  7  2022 ../
lrwxrwxrwx  1 root root    0 Jul  9 14:35 2-0051 -> '../../../../devices/platform/bus@f0000/bus@f0000:bus@b00000/2b200000.i2c/i2c-2/2-0051'/
lrwxrwxrwx  1 root root    0 Jul  9 14:35 module -> ../../../../module/at24/
--w-------  1 root root 4.0K Jul  9 14:35 bind
--w-------  1 root root 4.0K Apr  7  2022 uevent
--w-------  1 root root 4.0K Jul  9 14:35 unbind
```

<Note>
  In the folder name, `2` indicates that the EEPROM is on I2C bus 2 (i.e., wkup\_i2c0), and `0051` indicates
  that its I2C address is 0x51.
</Note>

In the example below, the file named `eeprom` is generated by the `at24` driver and allows accessing the
EEPROM as a file in Linux, enabling read and write operations.

```bash highlight=11 theme={"system"}
gemstone@t3-gem-o1:~$ ls /sys/bus/i2c/drivers/at24/2-0051/
total 0
drwxr-xr-x 4 root root    0 Apr  7  2022 ./
drwxr-xr-x 7 root root    0 Apr  7  2022 ../
drwxr-xr-x 3 root root    0 Apr  7  2022 2-00511/
lrwxrwxrwx 1 root root    0 Jul  9 14:54 driver -> ../../../../../../../bus/i2c/drivers/at24/
lrwxrwxrwx 1 root root    0 Jul  9 14:54 of_node -> '../../../../../../../firmware/devicetree/base/bus@f0000/bus@b00000/i2c@2b200000/eeprom@51'/
drwxr-xr-x 2 root root    0 Jul  9 14:54 power/
lrwxrwxrwx 1 root root    0 Apr  7  2022 subsystem -> ../../../../../../../bus/i2c/
lrwxrwxrwx 1 root root    0 Jul  9 14:54 supplier:regulator:regulator.0 -> ../../../../../../virtual/devlink/regulator:regulator.0--i2c:2-0051/
-rw------- 1 root root 4.0K Jul  9 14:54 eeprom
-r--r--r-- 1 root root 4.0K Jul  9 14:54 modalias
-r--r--r-- 1 root root 4.0K Apr  7  2022 name
-rw-r--r-- 1 root root 4.0K Apr  7  2022 uevent
```

### Using EEPROM via Terminal

The following command completely erases the EEPROM:

<Note>
  Since the EEPROM used on the T3-GEM-O1 board is 512 kilobits (64KiB), the count (number of bytes to write) is
  set to 65536 (64 x 1024).
</Note>

```bash theme={"system"}
gemstone@t3-gem-o1:~$ sudo dd if=/dev/zero of=/sys/bus/i2c/drivers/at24/2-0051/eeprom bs=1 count=65536 status=progress
[sudo] password for gemstone: 
65493 bytes (65 kB, 64 KiB) copied, 356 s, 0.2 kB/s
65536+0 records in
65536+0 records out
65536 bytes (66 kB, 64 KiB) copied, 356.235 s, 0.2 kB/s
```

<Note>
  As seen in the `dd` output, the EEPROM write speed is `0.2 kB/s`, meaning we can write 200 bytes per second.
  One disadvantage of EEPROMs is their very low write speed.
</Note>

The following command can be used to write data to the EEPROM:

```bash theme={"system"}
gemstone@t3-gem-o1:~$ echo "Gemstone EEPROM" | sudo tee /sys/bus/i2c/drivers/at24/2-0051/eeprom
[sudo] password for gemstone: 
Gemstone EEPROM
```

To perform a read operation, the following command can be executed:

```bash theme={"system"}
gemstone@t3-gem-o1:~$ sudo cat /sys/bus/i2c/drivers/at24/2-0051/eeprom
Gemstone EEPROM
```

For EEPROM read and write operations, examine the following usage examples in Python and C:

<CodeGroup>
  ```Python Python lines theme={"system"}
  #!/usr/bin/python3

  eeprom_dest = "/sys/bus/i2c/drivers/at24/2-0051/eeprom"
  eeprom_size = 65536

  # Write
  with open(eeprom_dest, "w") as eeprom:
      eeprom.write("Read-Write Example of EEPROM")

  # Read
  with open(eeprom_dest, "r") as eeprom:
      eeprom_data = eeprom.read(eeprom_size)
      print("EEPROM Data:", eeprom_data)
  ```

  ```C C/C++ lines theme={"system"}
  #include <stdio.h>

  #define EEPROM_SIZE 65536

  const char* EEPROM_DEST = "/sys/bus/i2c/drivers/at24/2-0051/eeprom";

  int main()
  {
      char eeprom_buffer[EEPROM_SIZE] = {0};
      
      // Write
      FILE* eeprom = fopen(EEPROM_DEST, "w");
      fprintf(eeprom, "Read-Write Example of EEPROM\n");
      fclose(eeprom);
      
      // Read
      eeprom = fopen(EEPROM_DEST, "r");
      fread(eeprom_buffer, 1, EEPROM_SIZE, eeprom);
      printf("Data: %s\n", eeprom_buffer);
      fclose(eeprom);
      
      return 0;
  }
  ```
</CodeGroup>