root/lm-sensors/trunk/doc/vid @ 1738

VID pin settings
--------------------

The VID (Voltage Identification) pins on sensor chips
are used to read the CPU Core voltage setting.

The VID setting can be controlled by jumpers on the board,
or, in newer motherboards, by settings in the BIOS.
On these newer boards, the BIOS programs some device's
pins which in turn controls a DC-DC Converter to set its
output to a certain voltage. These pins are also connected to
the sensor chip so that the VID setting can be read back
by applications.

There are generally 5 VID pins. The VID codes are defined
by Intel in documents titled
"VRM X.X DC-DC Converter Design Guidelines".
(VRM = Voltage Regulator Module)
These documents are available at http://developer.intel.com.

There are several different VRM document versions.
The common versions are as follows:

Document Version        Voltage Range   Increment       Processors
----------------        -------------   ---------       ----------
"2.4"                   0.8 - 1.55      0.025V          AMD Opteron 24x

8.2 (8.1, 8.3)          1.30 - 2.05V    0.05V           PII, PIII, Celeron
                        2.1 - 3.5V      0.10V

8.4                     1.30 - 2.05V    0.05V           PIII, Celeron
                                                        4 pins only

8.5                     1.050 - 1.825V  0.05V           PIII-S Tualatin

9.0, (9.1)              1.100 - 1.850V  0.025V          P4, AMD Socket A


"2.4" is not an actual document version but simply a way to identify
AMD Opteron 24x processors.
Note that versions 8.1 - 8.4 are compatible.

lm_sensors versions through 2.6.3 support only the VRM 8.2 standard.

Starting in lm_sensors 2.6.4 the VRM version is configurable.
To configure the sensor chip for the correct voltage range,
you must set the "vrm" correctly either via /proc or sensors.conf.

To be compatible with previous lm_sensors versions, the vrm defaults
to version 8.2.

To change the vrm version to 9.0, for example, do the following
after the chip module (in this example, w83781d) is loaded:

        echo 9.0 > /proc/sys/dev/sensors/w83781d-isa-0290/vrm

Alternatively, add a line in /etc/sensors.conf in the w83781d section:

        set vrm 9.0

and then, after the chip module is loaded, do:

        sensors -s

After this, reading the vid either by

        cat /proc/sys/dev/sensors/w83781d-isa-0290/vid

or by

        sensors

should show the new vid value.


The following values are legal vrm values:

        8.2, 8.4, 8.5, 9.0


Remember, the VID pins on the sensor chips are inputs only.
That means they can't be changed and there shouldn't be
any problems if you experiment with the vrm values until you
get it right.


Not all sensor chips have VID inputs.
For those that do, the VRM support status is listed below.

The following chip drivers support all the VRM versions via
/etc/sensors.conf and the vrm entry in /proc:

        adm1025, w83781d, lm87


The following chip drivers support only VRM 8.2 and cannot be changed:

        adm1024, it87, mtp008
        adm9240, gl520sm, lm78, maxilife

If you have a board with one of these chips which needs advanced
VRM support please email us.