TLV Writer Documentation

Overview

This script writes TLV (Tag-Length-Value) structured data into an I2C EEPROM. It supports a variety of system-specific keys that define metadata for the device.

The script:

Builds TLV-formatted payloads.
Writes the data into an EEPROM via I2C.
Supports custom-defined keys.
Calculates and appends a CRC checksum to ensure data integrity.

Usage

python3 TLV_write.py <i2c_bus> <eeprom_address> [--yes] <key> <value> <key> <value> ...

Finding the I2C Bus Number

To determine the correct I2C bus number, run the following command:

sudo i2cdetect -y 1

If no EEPROM device is found, repeat the command with different bus numbers (e.g., 2, 3, 4, etc.) until you detect an address 0x50 or 0x56. Once found, use the corresponding bus number in the script.

Example:

sudo i2cdetect -y 2

If the output shows:

     0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

Then bus 2 and address 0x50 should be used in the script.

Arguments

Argument	Description
i2c_bus	The I2C bus number.
eeprom_address	The EEPROM address (hex or decimal).
--yes (optional)	Automatically confirms the operation (skips user confirmation).
<key> <value>	One or more key-value pairs to write to EEPROM.

Example Usage

python3 TLV_write.py 2 0x50 TLV_CODE_SYS_NAME "MySystem" TLV_CODE_SYS_VERSION "1.0"

This writes:

System Name: "MySystem"
System Version: "1.0" to EEPROM at I2C bus 2, address 0x50.

Supported TLV Keys

Each TLV Key has a Hex Code, Max Length, and belongs to a DMIDecode Type.

System Information (DMIDecode Type: 1)

TLV Key	Hex Code	Max Length (bytes)
TLV_CODE_FAMILY	0x20	20
TLV_CODE_MANUF_DATE	0x23	10
TLV_CODE_PLATFORM_NAME	0x24	20
TLV_CODE_MANUF_NAME	0x25	20
TLV_CODE_VENDOR_NAME	0x27	20
TLV_CODE_SYS_NAME	0x30	20
TLV_CODE_SYS_SKU	0x31	20
TLV_CODE_SYS_SERIAL_NUMBER	0x32	24
TLV_CODE_SYS_VERSION	0x33	5

NIO Information (DMIDecode Type: 2)

TLV Key	Hex Code	Max Length (bytes)
TLV_CODE_NIO_NAME	0x40	20
TLV_CODE_NIO_SERIAL_NUMBER	0x41	24
TLV_CODE_NIO_VERSION	0x42	5

Chassis Information (DMIDecode Type: 3)

TLV Key	Hex Code	Max Length (bytes)
TLV_CODE_CHS_SERIAL_NUMBER	0x50	24
TLV_CODE_CHS_VERSION	0x51	5

TLV_CODE_CONFIG_CODE need to add

EEPROM Writing Process

Validate inputs: Ensure keys exist and values meet length constraints.
Format as TLV: Convert the data into TLV format with type, length, and value.
Append CRC Checksum: Ensure data integrity.
Clear EEPROM: Overwrite existing data with zeros before writing new content.
Write TLV data: Save formatted TLV data to the EEPROM via I2C.

Error Handling

If invalid input is provided, the script will:

Print an error message.
Exit without modifying EEPROM contents.

Common Errors

Error Message	Cause
`Error: Unknown key`	Provided TLV key is not in the supported list.
`Error: Value for key 'X' is too long`	Input exceeds the maximum allowed length.
`Error: MAC address must have 6 parts`	Incorrect MAC format.
`Error: I2C write error`	I2C communication issue during EEPROM write.
`Error: Total TLV data length exceeds EEPROM capacity`	Data is too large for EEPROM storage.

Dependencies

This script requires:

Python 3
smbus (I2C communication)
struct and binascii (binary manipulation)

To install missing dependencies:

sudo apt install python3-smbus

Notes

The script assumes EEPROM has a 256-byte capacity.
Page size is 16 bytes (writes are done in chunks).
The script calculates CRC-32 to ensure data integrity.