TLV Writer Documentation

---

Table of Contents

• Table of Contents

  • where to get
  • Overview
• Dependencies
• Usage

  • Arguments
  • Example Usage
  • Finding the I2C Bus Number
• Supported TLV Keys

  • System Information (SMBIOS Type 1)
  • NIO Information (SMBIOS Type 2)
  • Chassis Information (SMBIOS Type 3)
• Error Handling

  • Possible Errors

---

where to get

https://github.com/SolidRun/PyTLVWriter

Overview

This script writes TLV (Type-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.

---

Dependencies

To ensure all required dependencies are installed, run:

sudo apt update
sudo apt install python3 python3-smbus

this will:

• Install Python 3 if it is not already installed.
• Install smbus for I2C communication.

---

Usage

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

Arguments

Argument	Description
i2c_bus	The I2C bus number.
eeprom_address	The EEPROM address (hex or decimal).
--yes -y --force	Automatically confirms the operation (skips user confirmation).
-b	Writes the TLV data to a binary file (/tmp/eeprom_tlv.bin) without writing to the EEPROM. You can later write it manually using dd.
	One or more key-value pairs to write to EEPROM.

Example Usage

For example if we want the following data to appear in DMI:

Handle 0xXXXX, DMI type 1, XX bytes
System Information
	Manufacturer: XXXXX
	Product Name: MySystem
	Version: 1.0
	Serial Number: XXXXXX
	UUID: XXXXXX-XXXXX-XXXXX-XXXXX-XXXXX
	Wake-up Type: XXXXXXXXXXXX
	SKU Number: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
	Family: XXXXXXXXXXXXXXXXXXXXXXX

We want to run the following command (Note that bus 3 address 0X50 is used in this example):

python3 TLVwriter.py 3 0x50 TLV_CODE_SYS_NAME "MySystem" TLV_CODE_SYS_VERSION "1.0"

eeprom example for this :

python3 TLVwriter.py 3 0x50 TLV_CODE_SYS_NAME "EmbeddedDevice" \
TLV_CODE_SYS_SKU "ED-2024" \
TLV_CODE_SYS_SERIAL_NUMBER "SN123456789" \
TLV_CODE_SYS_VERSION "01.02" \
TLV_CODE_FAMILY "Industrial" \
TLV_CODE_MANUF_NAME "Solid-Run" \
TLV_CODE_MANUF_DATE "2024-03-11" \
TLV_CODE_PLATFORM_NAME "Bedrock-IPC"

00: 54 6c 76 49 6e 66 6f 00 01 65 00 30 0e 45 6d 62 TlvInfo.?e.0?Emb 10: 65 64 64 65 64 44 65 76 69 63 65 31 07 45 44 2d eddedDevice1?ED- 20: 32 30 32 34 32 0b 53 4e 31 32 33 34 35 36 37 38 20242?SN12345678 30: 39 33 05 30 31 2E 30 32 20 0a 49 6e 64 75 73 74 93?01.02 ?Indust 40: 72 69 61 6c 25 09 73 6f 6c 69 64 2d 72 75 6e 23 rial%.solid-run# 50: 0a 32 30 32 34 2d 30 33 2d 31 31 24 0b 42 65 64 .2024-03-11$.Bed 60: 72 6f 63 6b 2d 49 50 43 fe 04 6e 7e c0 fd 00 00 rock-IPC??n~?? 70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 80: …… header version Total Payload Length (little endian) Type Length Value crc checksum TLV

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., 3, 4, 5 etc.) until you detect an address 0x50 or 0x56. Once found, use the corresponding bus number in the script. Example:

sudo i2cdetect -y 3

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 3 and address 0x50 should be used in the script.

Bus 2 or 5 usually has the memory SPD on addresses 0x50 & 0x51, do not write to them!

---

Supported TLV Keys

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

System Information (SMBIOS Type 1)

TLV Key	Max Length (bytes)	BIOS path
TLV_CODE_FAMILY	20	-
TLV_CODE_MANUF_DATE	10	-
TLV_CODE_PLATFORM_NAME	20	-
TLV_CODE_MANUF_NAME	20	-
TLV_CODE_VENDOR_NAME	20	-
TLV_CODE_SYS_NAME	20	Main → Detailed Configuration Information → Model
TLV_CODE_SYS_SKU	20	Main screen
TLV_CODE_SYS_SERIAL_NUMBER	24	Main screen
TLV_CODE_SYS_VERSION	5	-

NIO Information (SMBIOS Type 2)

TLV Key	Max Length (bytes)
TLV_CODE_NIO_NAME	20
TLV_CODE_NIO_SERIAL_NUMBER	24
TLV_CODE_NIO_VERSION	5

Chassis Information (SMBIOS Type 3)

TLV Key	Max Length (bytes)
TLV_CODE_CHS_SERIAL_NUMBER	24
TLV_CODE_CHS_VERSION	5

TLV Key	Max Length (bytes)	BIOS path
TLV_CODE_CONFIG_CODE	200	Main → Detailed Configuration Information → Configuration String

---

Error Handling

If invalid input is provided, the script will:

• Print an error message.
• Exit without modifying EEPROM contents.

Possible 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.

---