Kernel driver eeprom

Supported chips:

  • Any EEPROM chip in the designated address range

    Prefix: ‘eeprom’

    Addresses scanned: I2C 0x50 - 0x57

    Datasheets: Publicly available from:

    Atmel (www.atmel.com), Catalyst (www.catsemi.com), Fairchild (www.fairchildsemi.com), Microchip (www.microchip.com), Philips (www.semiconductor.philips.com), Rohm (www.rohm.com), ST (www.st.com), Xicor (www.xicor.com), and others.

    Chip

    Size (bits)

    Address

    24C01

    1K

    0x50 (shadows at 0x51 - 0x57)

    24C01A

    1K

    0x50 - 0x57 (Typical device on DIMMs)

    24C02

    2K

    0x50 - 0x57

    24C04

    4K

    0x50, 0x52, 0x54, 0x56 (additional data at 0x51, 0x53, 0x55, 0x57)

    24C08

    8K

    0x50, 0x54 (additional data at 0x51, 0x52, 0x53, 0x55, 0x56, 0x57)

    24C16

    16K

    0x50 (additional data at 0x51 - 0x57)

    Sony

    2K

    0x57

    Atmel

    34C02B 2K

    0x50 - 0x57, SW write protect at 0x30-37

    Catalyst

    34FC02 2K

    0x50 - 0x57, SW write protect at 0x30-37

    Catalyst

    34RC02 2K

    0x50 - 0x57, SW write protect at 0x30-37

    Fairchild

    34W02 2K

    0x50 - 0x57, SW write protect at 0x30-37

    Microchip

    24AA52 2K

    0x50 - 0x57, SW write protect at 0x30-37

    ST

    M34C02 2K

    0x50 - 0x57, SW write protect at 0x30-37
Authors:

Description

This is a simple EEPROM module meant to enable reading the first 256 bytes of an EEPROM (on a SDRAM DIMM for example). However, it will access serial EEPROMs on any I2C adapter. The supported devices are generically called 24Cxx, and are listed above; however the numbering for these industry-standard devices may vary by manufacturer.

This module was a programming exercise to get used to the new project organization laid out by Frodo, but it should be at least completely effective for decoding the contents of EEPROMs on DIMMs.

DIMMS will typically contain a 24C01A or 24C02, or the 34C02 variants. The other devices will not be found on a DIMM because they respond to more than one address.

DDC Monitors may contain any device. Often a 24C01, which responds to all 8 addresses, is found.

Recent Sony Vaio laptops have an EEPROM at 0x57. We couldn’t get the specification, so it is guess work and far from being complete.

The Microchip 24AA52/24LCS52, ST M34C02, and others support an additional software write protect register at 0x30 - 0x37 (0x20 less than the memory location). The chip responds to “write quick” detection at this address but does not respond to byte reads. If this register is present, the lower 128 bytes of the memory array are not write protected. Any byte data write to this address will write protect the memory array permanently, and the device will no longer respond at the 0x30-37 address. The eeprom driver does not support this register.

Lacking functionality

  • Full support for larger devices (24C04, 24C08, 24C16). These are not typically found on a PC. These devices will appear as separate devices at multiple addresses.

  • Support for really large devices (24C32, 24C64, 24C128, 24C256, 24C512). These devices require two-byte address fields and are not supported.

  • Enable Writing. Again, no technical reason why not, but making it easy to change the contents of the EEPROMs (on DIMMs anyway) also makes it easy to disable the DIMMs (potentially preventing the computer from booting) until the values are restored somehow.

Use

After inserting the module (and any other required SMBus/i2c modules), you should have some EEPROM directories in /sys/bus/i2c/devices/* of names such as “0-0050”. Inside each of these is a series of files, the eeprom file contains the binary data from EEPROM.