JEDEC_DIMM(4)

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.mfg_week
    the week within the year in which the DIMM was manufactured

dev.jedec_dimm.X.mfg_year
    the year in which the DIMM was manufactured

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.mfg_week: 30
    dev.jedec_dimm.0.mfg_year: 17
    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.mfg_week: 13
    dev.jedec_dimm.6.mfg_year: 19
    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

You can use smbmsg(8) to probe for devices.

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
-nosplit 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>.