[lm-sensors] AMB FB DIMM driver

Jeffrey Garrett jgarrett at teamhpc.com
Wed May 23 02:05:59 CEST 2007

Attached is a rough approximation of a driver for the Intel AMB FB-DIMM
temperature sensors...

There is a somewhat lonely, but relevant ticket at

The sensors exposed on the 5000P chipsets are located in a contiguous
range of memory spanning 128k.  Logically, this space is split into 2k
blocks, each of which representing a potential DIMM.  The temperature
of a DIMM in this PCIish space is at function 3, offset 0x85.  That is,
you just have to read [base addr] + 2048*[dimm idx] + 3*256 + 0x85.
The temperature is in 0.5 deg C.  So for example, 0x10 = 8C.

To find the base address of this contiguous area of memory, all you have
to do is look at your PCI configuration...  It's exposed at device 16,
function 0, offset 0x48.  This is the device 0x8086:0x25f0.

To find your sensors, one can scan the 128k area of memory for what
"looks" right.  The ticket suggested looking for a vendor id of 0x8086
(Intel) starting the particular 2k slot.  This works on the DSBF-D, but
I have a Tyan board which is less agreeable.  But on both boards, the
non-DIMM areas in that space have vendor id:device id equal to
0xffff:0xffff.  In other words, we can just look for anything not all
ones.  I haven't found anything on paper that justifies this, but it
works on the boards I have.  ;)

The attached driver does pretty much just this:  it's linked to the
0x8086:0x25f0 id, and it looks in the configuration space for the base
address, and scans for valid areas.  It then exposes this via sysfs.
I used k8temp as a template.

It is a bit rough right now.  It did work with a recent vintage 2.6.20
kernel, on at least two different boards.

Comments/criticisms/flames welcome.

Jeff Garrett
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