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JEDEC_DIMM(4) Kernel Interfaces Manual 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 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.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 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 ad- dress 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 assem- bling multiple identical systems, as might be done by a system vendor. The mapping between bus/address and DIMM slot must first be deter- mined, 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 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>. FreeBSD ports 15.quarterly April 25, 2023 JEDEC_DIMM(4)
NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | COMPATIBILITY | SEE ALSO | STANDARDS | HISTORY | AUTHORS
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