eeprom.rst 4.4 KB

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  1. ====================
  2. Kernel driver eeprom
  3. ====================
  4. Supported chips:
  5. * Any EEPROM chip in the designated address range
  6. Prefix: 'eeprom'
  7. Addresses scanned: I2C 0x50 - 0x57
  8. Datasheets: Publicly available from:
  9. Atmel (www.atmel.com),
  10. Catalyst (www.catsemi.com),
  11. Fairchild (www.fairchildsemi.com),
  12. Microchip (www.microchip.com),
  13. Philips (www.semiconductor.philips.com),
  14. Rohm (www.rohm.com),
  15. ST (www.st.com),
  16. Xicor (www.xicor.com),
  17. and others.
  18. ========= ============= ============================================
  19. Chip Size (bits) Address
  20. ========= ============= ============================================
  21. 24C01 1K 0x50 (shadows at 0x51 - 0x57)
  22. 24C01A 1K 0x50 - 0x57 (Typical device on DIMMs)
  23. 24C02 2K 0x50 - 0x57
  24. 24C04 4K 0x50, 0x52, 0x54, 0x56
  25. (additional data at 0x51, 0x53, 0x55, 0x57)
  26. 24C08 8K 0x50, 0x54 (additional data at 0x51, 0x52,
  27. 0x53, 0x55, 0x56, 0x57)
  28. 24C16 16K 0x50 (additional data at 0x51 - 0x57)
  29. Sony 2K 0x57
  30. Atmel 34C02B 2K 0x50 - 0x57, SW write protect at 0x30-37
  31. Catalyst 34FC02 2K 0x50 - 0x57, SW write protect at 0x30-37
  32. Catalyst 34RC02 2K 0x50 - 0x57, SW write protect at 0x30-37
  33. Fairchild 34W02 2K 0x50 - 0x57, SW write protect at 0x30-37
  34. Microchip 24AA52 2K 0x50 - 0x57, SW write protect at 0x30-37
  35. ST M34C02 2K 0x50 - 0x57, SW write protect at 0x30-37
  36. ========= ============= ============================================
  37. Authors:
  38. - Frodo Looijaard <frodol@dds.nl>,
  39. - Philip Edelbrock <phil@netroedge.com>,
  40. - Jean Delvare <jdelvare@suse.de>,
  41. - Greg Kroah-Hartman <greg@kroah.com>,
  42. - IBM Corp.
  43. Description
  44. -----------
  45. This is a simple EEPROM module meant to enable reading the first 256 bytes
  46. of an EEPROM (on a SDRAM DIMM for example). However, it will access serial
  47. EEPROMs on any I2C adapter. The supported devices are generically called
  48. 24Cxx, and are listed above; however the numbering for these
  49. industry-standard devices may vary by manufacturer.
  50. This module was a programming exercise to get used to the new project
  51. organization laid out by Frodo, but it should be at least completely
  52. effective for decoding the contents of EEPROMs on DIMMs.
  53. DIMMS will typically contain a 24C01A or 24C02, or the 34C02 variants.
  54. The other devices will not be found on a DIMM because they respond to more
  55. than one address.
  56. DDC Monitors may contain any device. Often a 24C01, which responds to all 8
  57. addresses, is found.
  58. Recent Sony Vaio laptops have an EEPROM at 0x57. We couldn't get the
  59. specification, so it is guess work and far from being complete.
  60. The Microchip 24AA52/24LCS52, ST M34C02, and others support an additional
  61. software write protect register at 0x30 - 0x37 (0x20 less than the memory
  62. location). The chip responds to "write quick" detection at this address but
  63. does not respond to byte reads. If this register is present, the lower 128
  64. bytes of the memory array are not write protected. Any byte data write to
  65. this address will write protect the memory array permanently, and the
  66. device will no longer respond at the 0x30-37 address. The eeprom driver
  67. does not support this register.
  68. Lacking functionality
  69. ---------------------
  70. * Full support for larger devices (24C04, 24C08, 24C16). These are not
  71. typically found on a PC. These devices will appear as separate devices at
  72. multiple addresses.
  73. * Support for really large devices (24C32, 24C64, 24C128, 24C256, 24C512).
  74. These devices require two-byte address fields and are not supported.
  75. * Enable Writing. Again, no technical reason why not, but making it easy
  76. to change the contents of the EEPROMs (on DIMMs anyway) also makes it easy
  77. to disable the DIMMs (potentially preventing the computer from booting)
  78. until the values are restored somehow.
  79. Use
  80. ---
  81. After inserting the module (and any other required SMBus/i2c modules), you
  82. should have some EEPROM directories in ``/sys/bus/i2c/devices/*`` of names such
  83. as "0-0050". Inside each of these is a series of files, the eeprom file
  84. contains the binary data from EEPROM.