TLV Writer Documentation
Table of Contents
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:
this will:
Install Python 3 if it is not already installed.
Install smbus for I2C communication.
Usage
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:
We want to run the following command (Note that bus 3 address 0X50 is used in this example):
eeprom example for this :
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:
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:
If the output shows:
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.
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