Re: [PATCH] hysteresis for active cooling

["Francisco Figueiredo Jr." <fxjrlists-/E1597aS9LRfJ/NunPodnw@public.gmane.org>]

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Jamie Lentin wrote:
>>I don't know for sure, since I don't understand why your system starts
>>active cooling at 52 C (instead of 50 C) -- maybe there's hysteresis
>>in the hardware?  And why does it have to get way down to 44 C instead
>>of only 50 C before turning off?
> 
> 
> There is probably hysteresis built into the DSDT.  The ACPI Spec
> suggests doing this (don't have a page # handy tho', sorry), it's how
> hysteresis is implemented on my laptop (as well as yours---atlhough the
> hysteresis code is probably broken as it was on mine.  I'm preparing a
> page in the DSDT fixes/rewrites I've done on my laptop, if you're
> interested.  Your 600x DSDT code seems pretty much identical to my 770x
> code).
> 
> Basically, whenever there is a change in fan state, the DSDT can trigger
> the OS to re-read the trip-points from the DSDT, and give lower values.
> Again, once the fan turns off, it can tell the OS to re-read, and give
> higher trip-point values.
> 

Ahhhh, nice catch!

I never watched my trip points when fan was on.

This is what I get:
cat /proc/acpi/thermal_zone/THRM/trip_points
critical (S5):           93 C
passive:                 90 C: tc1=2 tc2=3 tsp=100 devices=0xdf6de240
active[0]:               70 C: devices=0xc147fe00
active[1]:               60 C: devices=0xc147ff20
active[2]:               45 C: devices=0xc147ffe0

Indeed, my active[2] was changed to 45 C. As I get my fan turned off
when it reaches 42, 41C I think it has the hysteresis already in my dsdt
as Jamie said. This would explain why values when fan is on or off
changes sometimes. I mean, sometimes my fan starts with 51C, other times
with 52C. The same happens when turning off.

Thanks guys for this one more information.



- --
Regards,

Francisco Figueiredo Jr.
Npgsql Lead Developer
http://gborg.postgresql.org/project/npgsql
MonoBrasil Project Founder Member
http://monobrasil.softwarelivre.org


- -------------
"Science without religion is lame;
religion without science is blind."

                  ~ Albert Einstein
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