TLVwriter

A command-line Python tool to read and write TLV (Type-Length-Value) data to an I²C EEPROM and manage a CONFIG_CODE EFI variable via efivarfs.

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Overview

TLVwriter.py facilitates:

• Reading existing TLV data from an EEPROM and displaying it in human-readable form.
• Building a TLV binary blob from <key> <value> pairs.
• Writing the TLV blob into EEPROM in page-sized chunks (default 16 B pages).
• Clearing EEPROM contents before writing new data.
• Creating or updating a CONFIG_CODE EFI variable under /sys/firmware/efi/efivars.
• Colored output for errors (red), warnings (yellow), info(cyan) and success (green).

This is useful for BIOS/hardware inventory, factory programming, and secure-boot configurations.

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Requirements

• Python 3.6+
• Root privileges (required for I²C access and EFI variable operations)
• Linux with UEFI and efivarfs mounted at /sys/firmware/efi/efivars
• smbus (typically provided by python3-smbus or python3-smbus2)
• An I²C EEPROM of at least 256 bytes capacity on a known bus/address

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Installation

1. Clone this repository:

   git clone https://github.com/youruser/TLVwriter.git
   cd TLVwriter

2. Install dependencies:

   sudo apt-get install python3-smbus
   # or via pip if using smbus2:
   pip install smbus2

3. Ensure efivarfs is mounted:

   sudo mountpoint -q /sys/firmware/efi/efivars || \
     sudo mount -t efivarfs efivarfs /sys/firmware/efi/efivars

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TLV Format

Header (11 bytes total)

Offset	Size	Description
0	8	ASCII signature: 'TlvInfo' padded to 8 bytes
8	1	Version (currently 0x01)
9–10	2	Payload length (little-endian 16-bit integer)

Payload (variable length)

A sequence of entries, each:

1. Type (1 byte): TLV code
2. Length (1 byte): number of bytes in Value
3. Value (N bytes)

After all entries, a CRC entry is appended:

• Type 0xFE (CRC code)
• Length 0x04
• Value: 4 bytes of little-endian CRC32 computed over all prior bytes (header + payload before CRC field)

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Supported TLV Keys

Below are the BIOS/hardware keys you can specify, along with their TLV codes and maximum lengths:

KEY                          | 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_NIO_TYPE            | 0x28 | 8
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
TLV_CODE_SYS_UUID            | 0x34 | 36
TLV_CODE_NIO_NAME            | 0x40 | 20
TLV_CODE_NIO_SERIAL_NUMBER   | 0x41 | 24
TLV_CODE_NIO_VERSION         | 0x42 | 5
TLV_CODE_CHS_SERIAL_NUMBER   | 0x50 | 24
TLV_CODE_CHS_VERSION         | 0x51 | 5
TLV_CODE_CONFIG_CODE         | 0x60 | 200  ← only writes EFI variable since EEPROM is too small

Entries exceeding their maximum length will be rejected.

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Usage

sudo python3 TLVwriter.py <i2c_bus> <eeprom_addr> [options] <key1> <val1> [<key2> <val2> ...]

Arguments:

• <i2c_bus>: integer bus number (e.g. 1 for /dev/i2c-1).
• <eeprom_addr>: I²C address in hex or decimal (e.g. 0x50).
• <key> <value>: one or more TLV field specifiers.

Options:

• -r, --read : Read and display existing TLV data from EEPROM.
• -y, --yes : Skip confirmation prompt before overwrite.
• -b, --binary : Write TLV blob to /tmp/eeprom_tlv.bin instead of EEPROM.

Examples:

1. Read current TLV from EEPROM:

   sudo python3 TLVwriter.py 1 0x50 -r

2. Write system metadata:

   sudo python3 TLVwriter.py 1 0x50 \
     TLV_CODE_SYS_NAME "MyBoard" \
     TLV_CODE_SYS_UUID "123e4567-e89b-12d3-a456-426655440000" \
     -y

3. Generate binary only (no EEPROM write):

   sudo python3 TLVwriter.py 1 0x50 -b TLV_CODE_PLATFORM_NAME "ProtoSys" -y