108 lines
4.4 KiB
ReStructuredText
108 lines
4.4 KiB
ReStructuredText
====================
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Kernel driver eeprom
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====================
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Supported chips:
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* Any EEPROM chip in the designated address range
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Prefix: 'eeprom'
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Addresses scanned: I2C 0x50 - 0x57
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Datasheets: Publicly available from:
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Atmel (www.atmel.com),
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Catalyst (www.catsemi.com),
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Fairchild (www.fairchildsemi.com),
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Microchip (www.microchip.com),
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Philips (www.semiconductor.philips.com),
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Rohm (www.rohm.com),
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ST (www.st.com),
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Xicor (www.xicor.com),
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and others.
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========= ============= ============================================
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Chip Size (bits) Address
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========= ============= ============================================
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24C01 1K 0x50 (shadows at 0x51 - 0x57)
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24C01A 1K 0x50 - 0x57 (Typical device on DIMMs)
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24C02 2K 0x50 - 0x57
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24C04 4K 0x50, 0x52, 0x54, 0x56
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(additional data at 0x51, 0x53, 0x55, 0x57)
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24C08 8K 0x50, 0x54 (additional data at 0x51, 0x52,
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0x53, 0x55, 0x56, 0x57)
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24C16 16K 0x50 (additional data at 0x51 - 0x57)
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Sony 2K 0x57
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Atmel 34C02B 2K 0x50 - 0x57, SW write protect at 0x30-37
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Catalyst 34FC02 2K 0x50 - 0x57, SW write protect at 0x30-37
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Catalyst 34RC02 2K 0x50 - 0x57, SW write protect at 0x30-37
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Fairchild 34W02 2K 0x50 - 0x57, SW write protect at 0x30-37
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Microchip 24AA52 2K 0x50 - 0x57, SW write protect at 0x30-37
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ST M34C02 2K 0x50 - 0x57, SW write protect at 0x30-37
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========= ============= ============================================
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Authors:
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- Frodo Looijaard <frodol@dds.nl>,
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- Philip Edelbrock <phil@netroedge.com>,
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- Jean Delvare <jdelvare@suse.de>,
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- Greg Kroah-Hartman <greg@kroah.com>,
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- IBM Corp.
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Description
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-----------
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This is a simple EEPROM module meant to enable reading the first 256 bytes
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of an EEPROM (on a SDRAM DIMM for example). However, it will access serial
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EEPROMs on any I2C adapter. The supported devices are generically called
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24Cxx, and are listed above; however the numbering for these
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industry-standard devices may vary by manufacturer.
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This module was a programming exercise to get used to the new project
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organization laid out by Frodo, but it should be at least completely
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effective for decoding the contents of EEPROMs on DIMMs.
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DIMMS will typically contain a 24C01A or 24C02, or the 34C02 variants.
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The other devices will not be found on a DIMM because they respond to more
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than one address.
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DDC Monitors may contain any device. Often a 24C01, which responds to all 8
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addresses, is found.
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Recent Sony Vaio laptops have an EEPROM at 0x57. We couldn't get the
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specification, so it is guess work and far from being complete.
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The Microchip 24AA52/24LCS52, ST M34C02, and others support an additional
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software write protect register at 0x30 - 0x37 (0x20 less than the memory
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location). The chip responds to "write quick" detection at this address but
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does not respond to byte reads. If this register is present, the lower 128
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bytes of the memory array are not write protected. Any byte data write to
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this address will write protect the memory array permanently, and the
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device will no longer respond at the 0x30-37 address. The eeprom driver
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does not support this register.
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Lacking functionality
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---------------------
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* Full support for larger devices (24C04, 24C08, 24C16). These are not
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typically found on a PC. These devices will appear as separate devices at
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multiple addresses.
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* Support for really large devices (24C32, 24C64, 24C128, 24C256, 24C512).
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These devices require two-byte address fields and are not supported.
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* Enable Writing. Again, no technical reason why not, but making it easy
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to change the contents of the EEPROMs (on DIMMs anyway) also makes it easy
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to disable the DIMMs (potentially preventing the computer from booting)
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until the values are restored somehow.
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Use
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---
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After inserting the module (and any other required SMBus/i2c modules), you
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should have some EEPROM directories in ``/sys/bus/i2c/devices/*`` of names such
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as "0-0050". Inside each of these is a series of files, the eeprom file
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contains the binary data from EEPROM.
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