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     jedec_dimm — report asset information and temperatures for JEDEC DDR3 / DDR4 DIMMs


           device jedec_dimm
           device smbus

     Alternatively, to load the driver as a module at boot time, place the following line in


     Addressing information must be manually specified in /boot/device.hints:



     The jedec_dimm driver reports asset information (Part Number, Serial Number) encoded in the
     “Serial Presence Detect” (SPD) data on JEDEC DDR3 and DDR4 DIMMs.  It also calculates and
     reports the memory capacity of the DIMM, in megabytes.  If the DIMM includes a “Thermal
     Sensor On DIMM” (TSOD), the temperature is also reported.

     The jedec_dimm driver accesses the SPD and TSOD over the smbus(4).

     The data is reported via a sysctl(8) interface; all values are read-only:

     dev.jedec_dimm.X.%desc     a string description of the DIMM, including TSOD and slotid info
                                if present.

     dev.jedec_dimm.X.capacity  the DIMM's memory capacity, in megabytes

     dev.jedec_dimm.X.part      the manufacturer's part number of the DIMM

     dev.jedec_dimm.X.serial    the manufacturer's serial number of the DIMM

     dev.jedec_dimm.X.slotid    a copy of the corresponding hint, if set

     dev.jedec_dimm.X.temp      if a TSOD is present, the reported temperature

     dev.jedec_dimm.X.type      the DIMM type (DDR3 or DDR4)

     These values are configurable for jedec_dimm via device.hints(5):      the smbus(4) to which the DIMM is connected

     hint.jedec_dimm.X.addr    the SMBus address of the SPD.  JEDEC specifies that the four most-
                               significant bits of the address are the “Device Type Identifier”
                               (DTI), and that the DTI of the SPD is 0xa.  Since the least-
                               significant bit of an SMBus address is the read/write bit, and is
                               always written as 0, that means the four least-significant bits of
                               the address must be even.

     hint.jedec_dimm.X.slotid  optional slot identifier.  If populated with the DIMM slot name
                               silkscreened on the motherboard, this provides a mapping between
                               the DIMM slot name and the DIMM serial number.  That mapping is
                               useful for detailed asset tracking, and makes it easier to
                               physically locate a specific DIMM when doing a replacement.  This
                               is useful when assembling multiple identical systems, as might be
                               done by a system vendor.  The mapping between bus/address and DIMM
                               slot must first be determined, either through motherboard
                               documentation or trial-and-error.

     If the DIMMs are on an I2C bus behind an iicbus(4) controller, then the iicsmb(4) bridge
     driver can be used to attach the smbus(4).


     Consider two DDR4 DIMMs with the following hints:



     Their sysctl(8) output (sorted):

           dev.jedec_dimm.0.%desc: DDR4 DIMM w/ Atmel TSOD (A1)
           dev.jedec_dimm.0.%driver: jedec_dimm
           dev.jedec_dimm.0.%location: addr=0xa0
           dev.jedec_dimm.0.%parent: smbus0
           dev.jedec_dimm.0.capacity: 16384
           dev.jedec_dimm.0.part: 36ASF2G72PZ-2G1A2
           dev.jedec_dimm.0.serial: 0ea815de
           dev.jedec_dimm.0.slotid: A1
           dev.jedec_dimm.0.temp: 32.7C
           dev.jedec_dimm.0.type: DDR4

           dev.jedec_dimm.6.%desc: DDR4 DIMM w/ TSE2004av compliant TSOD
           dev.jedec_dimm.6.%driver: jedec_dimm
           dev.jedec_dimm.6.%location: addr=0xa8
           dev.jedec_dimm.6.%parent: smbus1
           dev.jedec_dimm.6.capacity: 8192
           dev.jedec_dimm.6.part: VRA9MR8B2H1603
           dev.jedec_dimm.6.serial: 0c4c46ad
           dev.jedec_dimm.6.temp: 43.1C
           dev.jedec_dimm.6.type: DDR4


     jedec_dimm implements a superset of the functionality of the now-deleted jedec_ts(4).  Hints
     for jedec_ts(4) can be mechanically converted for use with jedec_dimm.  Two changes are

     1.   In all jedec_ts(4) hints, replace “jedec_ts” with “jedec_dimm”

     2.   In jedec_ts(4) “addr” hints, replace the TSOD DTI “0x3” with the SPD DTI “0xa”

     The following sed(1) script will perform the necessary changes:

           sed -i ".old" -e 's/jedec_ts/jedec_dimm/' \
               -e '/jedec_dimm/s/addr="0x3/addr="0xa/' /boot/device.hints


     iicbus(4), iicsmb(4), smbus(4), sysctl(8)


     (DDR3 SPD) JEDEC, Standard 21-C, Annex K.

     (DDR3 TSOD) JEDEC, Standard 21-C, TSE2002av.

     (DDR4 SPD) JEDEC, Standard 21-C, Annex L.

     (DDR4 TSOD) JEDEC, Standard 21-C, TSE2004av.


     The jedec_dimm driver first appeared in FreeBSD 12.0.


     The jedec_dimm driver and this manual page were written by Ravi Pokala
     <>.  They are both based in part on the now-deleted jedec_ts(4) driver
     and manual page, written by Andriy Gapon <>.