NAME

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

SYNOPSIS

           device jedec_dimm
           device smbus

     Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):

           jedec_dimm_load="YES"

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

           hint.jedec_dimm.0.at="smbus0"
           hint.jedec_dimm.0.addr="0xa0"
           hint.jedec_dimm.0.slotid="Silkscreen"

DESCRIPTION

     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):

     hint.jedec_dimm.X.at      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).

EXAMPLES

     Consider two DDR4 DIMMs with the following hints:

           hint.jedec_dimm.0.at="smbus0"
           hint.jedec_dimm.0.addr="0xa0"
           hint.jedec_dimm.0.slotid="A1"

           hint.jedec_dimm.6.at="smbus1"
           hint.jedec_dimm.6.addr="0xa8"

     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.%pnpinfo:
           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.%pnpinfo:
           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

COMPATIBILITY

     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 required:

     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

SEE ALSO

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

STANDARDS

     (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.

HISTORY

     The jedec_dimm driver first appeared in FreeBSD 12.0.

AUTHORS

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