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<table class="head">
<tr>
<td class="head-ltitle">JEDEC_DIMM(4)</td>
<td class="head-vol">Device Drivers Manual</td>
<td class="head-rtitle">JEDEC_DIMM(4)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">jedec_dimm</code> —
<span class="Nd">report asset information and temperatures for JEDEC DDR3 /
DDR4 DIMMs</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<div class="Bd Bd-indent"><code class="Cd">device jedec_dimm</code>
<br/>
<code class="Cd">device smbus</code></div>
<p class="Pp">Alternatively, to load the driver as a module at boot time, place
the following line in <a class="Xr">loader.conf(5)</a>:</p>
<div class="Bd Pp Bd-indent Li">
<pre>jedec_dimm_load="YES"</pre>
</div>
<p class="Pp">Addressing information must be manually specified in
<span class="Pa">/boot/device.hints</span>:</p>
<div class="Bd Pp Bd-indent Li">
<pre><code class="Cd">hint.jedec_dimm.0.at="smbus0"</code>
<br/>
<code class="Cd">hint.jedec_dimm.0.addr="0xa0"</code>
<br/>
<code class="Cd">hint.jedec_dimm.0.slotid="Silkscreen"</code></pre>
</div>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">The <code class="Nm">jedec_dimm</code> 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.</p>
<p class="Pp">The <code class="Nm">jedec_dimm</code> driver accesses the SPD and
TSOD over the <a class="Xr">smbus(4)</a>.</p>
<p class="Pp">The data is reported via a <a class="Xr">sysctl(8)</a> interface;
all values are read-only:</p>
<dl class="Bl-tag">
<dt id="dev.jedec_dimm.X._desc"><var class="Va">dev.jedec_dimm.X.%desc</var></dt>
<dd>a string description of the DIMM, including TSOD and slotid info if
present.</dd>
<dt id="dev.jedec_dimm.X.capacity"><var class="Va">dev.jedec_dimm.X.capacity</var></dt>
<dd>the DIMM's memory capacity, in megabytes</dd>
<dt id="dev.jedec_dimm.X.mfg_week"><var class="Va">dev.jedec_dimm.X.mfg_week</var></dt>
<dd>the week within the year in which the DIMM was manufactured</dd>
<dt id="dev.jedec_dimm.X.mfg_year"><var class="Va">dev.jedec_dimm.X.mfg_year</var></dt>
<dd>the year in which the DIMM was manufactured</dd>
<dt id="dev.jedec_dimm.X.part"><var class="Va">dev.jedec_dimm.X.part</var></dt>
<dd>the manufacturer's part number of the DIMM</dd>
<dt id="dev.jedec_dimm.X.serial"><var class="Va">dev.jedec_dimm.X.serial</var></dt>
<dd>the manufacturer's serial number of the DIMM</dd>
<dt id="dev.jedec_dimm.X.slotid"><var class="Va">dev.jedec_dimm.X.slotid</var></dt>
<dd>a copy of the corresponding hint, if set</dd>
<dt id="dev.jedec_dimm.X.temp"><var class="Va">dev.jedec_dimm.X.temp</var></dt>
<dd>if a TSOD is present, the reported temperature</dd>
<dt id="dev.jedec_dimm.X.type"><var class="Va">dev.jedec_dimm.X.type</var></dt>
<dd>the DIMM type (DDR3 or DDR4)</dd>
</dl>
<p class="Pp">These values are configurable for
<code class="Nm">jedec_dimm</code> via
<a class="Xr">device.hints(5)</a>:</p>
<dl class="Bl-tag">
<dt id="hint.jedec_dimm.X.at"><var class="Va">hint.jedec_dimm.X.at</var></dt>
<dd>the <a class="Xr">smbus(4)</a> to which the DIMM is connected</dd>
<dt id="hint.jedec_dimm.X.addr"><var class="Va">hint.jedec_dimm.X.addr</var></dt>
<dd>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.</dd>
<dt id="hint.jedec_dimm.X.slotid"><var class="Va">hint.jedec_dimm.X.slotid</var></dt>
<dd>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.</dd>
</dl>
<p class="Pp">If the DIMMs are on an I2C bus behind an
<a class="Xr">iicbus(4)</a> controller, then the <a class="Xr">iicsmb(4)</a>
bridge driver can be used to attach the <a class="Xr">smbus(4)</a>.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="EXAMPLES"><a class="permalink" href="#EXAMPLES">EXAMPLES</a></h1>
<p class="Pp">Consider two DDR4 DIMMs with the following hints:</p>
<div class="Bd Pp Bd-indent Li">
<pre>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"</pre>
</div>
<p class="Pp">Their <a class="Xr">sysctl(8)</a> output (sorted):</p>
<div class="Bd Pp Bd-indent Li">
<pre>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</pre>
</div>
<p class="Pp">You can use <a class="Xr">smbmsg(8)</a> to probe for devices.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="COMPATIBILITY"><a class="permalink" href="#COMPATIBILITY">COMPATIBILITY</a></h1>
<p class="Pp"><code class="Nm">jedec_dimm</code> implements a superset of the
functionality of the now-deleted <a class="Xr">jedec_ts(4)</a>. Hints for
<a class="Xr">jedec_ts(4)</a> can be mechanically converted for use with
<code class="Nm">jedec_dimm</code>. Two changes are required:</p>
<ol class="Bl-enum">
<li>In all <a class="Xr">jedec_ts(4)</a> hints, replace
“jedec_ts” with “jedec_dimm”</li>
<li>In <a class="Xr">jedec_ts(4)</a> “addr” hints, replace the
TSOD DTI “0x3” with the SPD DTI “0xa”</li>
</ol>
<p class="Pp">The following <a class="Xr">sed(1)</a> script will perform the
necessary changes:</p>
<div class="Bd Pp Bd-indent Li">
<pre>sed -i ".old" -e 's/jedec_ts/jedec_dimm/' \
-e '/jedec_dimm/s/addr="0x3/addr="0xa/' /boot/device.hints</pre>
</div>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">iicbus(4)</a>, <a class="Xr">iicsmb(4)</a>,
<a class="Xr">smbus(4)</a>, <a class="Xr">sysctl(8)</a></p>
</section>
<section class="Sh">
<h1 class="Sh" id="STANDARDS"><a class="permalink" href="#STANDARDS">STANDARDS</a></h1>
<p class="Pp"><cite class="Rs">(DDR3 SPD) <span class="RsA">JEDEC</span>,
<span class="RsT">Standard 21-C, Annex K</span>.</cite></p>
<p class="Pp"><cite class="Rs">(DDR3 TSOD) <span class="RsA">JEDEC</span>,
<span class="RsT">Standard 21-C, TSE2002av</span>.</cite></p>
<p class="Pp"><cite class="Rs">(DDR4 SPD) <span class="RsA">JEDEC</span>,
<span class="RsT">Standard 21-C, Annex L</span>.</cite></p>
<p class="Pp"><cite class="Rs">(DDR4 TSOD) <span class="RsA">JEDEC</span>,
<span class="RsT">Standard 21-C, TSE2004av</span>.</cite></p>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">The <code class="Nm">jedec_dimm</code> driver first appeared in
<span class="Ux">FreeBSD 12.0</span>.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="AUTHORS"><a class="permalink" href="#AUTHORS">AUTHORS</a></h1>
<p class="Pp">The <code class="Nm">jedec_dimm</code> driver and this manual page
were written by <span class="An">Ravi Pokala</span>
<<a class="Mt" href="mailto:rpokala@freebsd.org">rpokala@freebsd.org</a>>.
They are both based in part on the now-deleted <a class="Xr">jedec_ts(4)</a>
driver and manual page, written by <span class="An">Andriy Gapon</span>
<<a class="Mt" href="mailto:avg@FreeBSD.org">avg@FreeBSD.org</a>>.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">January 2, 2026</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
