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JEDEC_DIMM(4)	       FreeBSD Kernel Interfaces Manual		 JEDEC_DIMM(4)

     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 loader.conf(5):


     Addressing	information must be manually specified in /boot/device.hints:"smbus0"

     The jedec_dimm driver reports asset information (Part Number, Serial Num-
     ber) 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 ad-
			       dress 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 mother-
			       board, 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 spe-
			       cific DIMM when doing a replacement.  This is
			       useful when assembling multiple identical sys-
			       tems, 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:"smbus0"

     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 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

     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

FreeBSD	13.0			 July 31, 2018			  FreeBSD 13.0


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