GSoC2007: cnst-sensors.2007-09-13.patch

[Chuck Swiger]

On Sep 21, 2007, at 9:16 AM, Rui Paulo wrote:
> On 21 Sep 2007, at 00:12, Doug Barton wrote:
>> On Wed, 19 Sep 2007, Constantine A. Murenin wrote:
>>> Thanks for testing!
>>
>> Glad to help. In case it's interesting, I was doing the xorg  
>> update with portmaster last night and I got several "PROCHOT  
>> asserted" messages on my console at different times. I'm assuming  
>> that's expected behavior, just curious if it's something bad, as  
>> in when that happens it's time to turn off the laptop? (I didn't  
>> seem them when the happened, they were there when I got back to  
>> check on the compiling.)
>
> That basically means the digital sensor has detected a high  
> temperature and it allows the operating system to do "something". I  
> plan to work a bit more on coretemp(4) so that all these  
> notifications go through devctl(4).

The CPU itself has a thermal control circuit which puts the CPU into  
a reduced duty cycle (ie, it reduces the core voltage and stops the  
CPU for something like 10 clocks, and then allows one clock through)  
and continues to run the CPU at about 10% of normal workload until  
the temperature falls below the critical threshold.  There's a good  
document here:

   http://www.intel.com/technology/magazine/computing/it04021.pdf

[ There are plenty of others handy if you do a search on Intel's  
website, but that particular link is short and readable compared with  
the processor spec docs.  :-) ]

The threshold temperature varies depending on the exact part, but is  
generally around 65 Celsius-- and is hot enough that you don't really  
want to encounter it in normal operation, as it's a sign that cooling  
is not adequate for the system to continue to operate safely at full  
speed.  Most of the Intel CPUs also include a second thermal circuit  
called THERMTRIP which fires around 95 Celsius which will shut the  
CPU down entirely to prevent a catastrophic failure.

A longer article is here:

   http://www.intel.com/technology/itj/2006/volume10issue02/ 
art03_power_and_thermal_management/p03_power_management.htm

-- 
-Chuck