Re: [lm-sensors] Wrong temperatures reported for Core2Duo CPU in

[Hubert Kario <hka@qbs.com.pl>]

On Friday 12 March 2010 10:40:48 Luca Tettamanti wrote:
> On Wed, Mar 10, 2010 at 7:10 PM, Jean Delvare <khali@linux-fr.org> wrote:
> > On Wed, 10 Mar 2010 08:41:52 -0800, lmsensorslist@nodivisions.com wrote:
> >> OK, I just tested this, by running the "stress" command for a few
> >> minutes, until the coretemp values were 91C and 92C.  I then
> >> immediately shut down and went into the BIOS.  Here's the BIOS numbers:
> >> 
> >> 68C CPU Die/Package Temperature
> >> 54C Motherboard Temperature
> >> 44C Motherboard Temperature
> >> 82C ICH Temperature
> >> 58C MCH Temperature
> >> 
> >> And here's the same BIOS numbers after sitting there in the BIOS for 10
> >> minutes:
> >> 
> >> 63C CPU Die/Package Temperature
> >> 50C Motherboard Temperature
> >> 44C Motherboard Temperature
> >> 83C ICH Temperature
> >> 54C MCH Temperature
> >> 
> >> I guess the die temp is the one that corresponds to the CPU?
> > 
> > Yes, it probably comes from the CPU internal sensors, although only
> > disassembling the BIOS could tell for sure.
> 
> From my experience on Asus boards the "CPU" temperature shown in the
> BIOS is usually read from the external monitoring chip, and only
> rarely from the CPU itself (using PECI - with a totally wrong tjmax -
> sigh).
> The ICH temperature is also suspiciously high.

There are three sensors in C2D processors - two T junction, and one Tcase

Tcase is read by mainboard, the die has only the sensor, as it was since the 
days of PIII if I recall right
Tjunction are read using internal CPU circuits.

Some programs use the Tj and some use Tcase as the value for "CPU temp".

The usual location for Tcase is between the cores, on top of the silicon die, 
Tjunction reside in ALU, theoretically in the place that can become the 
hottest under load.

With good heat spreader and correctly applied thermal paste the difference 
between them shouldn't differ by more than 1-3C idle and 3-5C on load. If it 
does, the heat spreader isn't placed corretly or there are air bubbles in the 
paste.
But more commonly it means that the sensors aren't calibrated properly.

The correct temperatures for C2D and C2Q chips at idle (with all power saving 
features ON) are about 4-5C above ambient for Tcase and 6-7C above ambient for 
TJunction.

Look on overclocking forums for more information, they usually dig the deepest 
for such info :)
-- 
Hubert Kario
QBS - Quality Business Software
ul. Ksawerów 30/85
02-656 Warszawa
POLAND
tel. +48 (22) 646-61-51, 646-74-24
fax +48 (22) 646-61-50

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