====== SPD information under Linux ======

[[wp>Serial_Presence_Detect|Quoted]] from Wikipedia: "Serial Presence Detect (SPD) refers to a standardized way to automatically access information about a computer memory module". This means, it is possible by software to get information about memory modules available on your computer. This information include: manufacturer, model, size, speed, [[wp>CAS_Latency|CAS latency]], manufacturing date to name a few. This can be handy to verify the specifications of a newly bought memory module, to get information useful for overclocking and to  get its serial number for archiving purposes (useful for inventories).


===== Reading data =====

Under Linux, [[http://www.lm-sensors.org/|lm-sensors]] does a good job reading this information from the chips. The kernel module named ''eeprom''((Just ''# modprobe eeprom'' should work.)) acquires such information and exposes it via [[wp>Sysfs]] at ''/sys/bus/i2c/drivers/eeprom/''. The problem is that this information is stored in a specific format (looks like garbage for humans). However, lm-sensors comes with an utility called ''decode-dimms.pl'' that is able to decode the information for us humans. It can be found at ''prog/eeprom/decode-dimms.pl'' on the lm-sensors source tree. Debian systems usually ship it together the [[http://packages.debian.org/stable/utils/lm-sensors|package]] at ''/usr/share/doc/lm-sensors/examples/eeprom/decode-dimms.pl''.

As of version 3.0.0, the ''decode-dimms.pl'' script has moved to a separate package named [[http://www.lm-sensors.org/wiki/I2CTools|i2c-tools]], where it can be found under the ''eeprom'' directory.

===== Example =====

Here is an example output for my Compaq Presario notebook:

  $ /usr/share/doc/lm-sensors/examples/eeprom/decode-dimms.pl
  
  Memory Serial Presence Detect Decoder
  By Philip Edelbrock, Christian Zuckschwerdt, Burkart Lingner,
  Jean Delvare and others
  Version 2.10.1
  
  
  Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/0-0050
  Guessing DIMM is in                             bank 1
  
  ---=== SPD EEPROM Information ===---
  EEPROM Checksum of bytes 0-62                   OK (0x33)
  # of bytes written to SDRAM EEPROM              128
  Total number of bytes in EEPROM                 256
  Fundamental Memory type                         DDR SDRAM
  SPD Revision                                    0.0
  
  ---=== Memory Characteristics ===---
  Maximum module speed                            333MHz (PC2700)
  Size                                            256 MB
  tCL-tRCD-tRP-tRAS                               2.5-3-3-7
  Supported CAS Latencies                         2.5, 2
  Supported CS Latencies                          0
  Supported WE Latencies                          1
  Minimum Cycle Time (CAS 2.5)                    6 ns
  Maximum Access Time (CAS 2.5)                   0.7 ns
  Minimum Cycle Time (CAS 2)                      7.5 ns
  Maximum Access Time (CAS 2)                     0.7 ns
  
  ---=== Manufacturing Information ===---
  Manufacturer                                    ProMos/Mosel Vitelic
  Manufacturing Location Code                     0x02
  Part Number                                     V826632B24SCTG-C0
  Manufacturing Date                              2005-W23
  Assembly Serial Number                          0x32162D00
  
  
  Decoding EEPROM: /sys/bus/i2c/drivers/eeprom/0-0051
  Guessing DIMM is in                             bank 2
  
  ---=== SPD EEPROM Information ===---
  EEPROM Checksum of bytes 0-62                   OK (0x33)
  # of bytes written to SDRAM EEPROM              128
  Total number of bytes in EEPROM                 256
  Fundamental Memory type                         DDR SDRAM
  SPD Revision                                    0.0
  
  ---=== Memory Characteristics ===---
  Maximum module speed                            333MHz (PC2700)
  Size                                            256 MB
  tCL-tRCD-tRP-tRAS                               2.5-3-3-7
  Supported CAS Latencies                         2.5, 2
  Supported CS Latencies                          0
  Supported WE Latencies                          1
  Minimum Cycle Time (CAS 2.5)                    6 ns
  Maximum Access Time (CAS 2.5)                   0.7 ns
  Minimum Cycle Time (CAS 2)                      7.5 ns
  Maximum Access Time (CAS 2)                     0.7 ns
  
  ---=== Manufacturing Information ===---
  Manufacturer                                    ProMos/Mosel Vitelic
  Manufacturing Location Code                     0x02
  Part Number                                     V826632B24SCTG-C0
  Manufacturing Date                              2005-W23
  Assembly Serial Number                          0xE6142D00
  
  
  Number of SDRAM DIMMs detected and decoded: 2


===== References =====

Please refer to [[http://www.lm-sensors.org/|lm-sensors]]'s documentation for more details. Documentation regarding the ''eeprom'' module can be found on it's source tree at ''doc/chips/eeprom''. Debian systems usually ship it together the [[http://packages.debian.org/stable/utils/lm-sensors|package]] at ''/usr/share/doc/lm-sensors/doc/chips/eeprom.gz''.