[maemo-developers] Where are the N900 "too much time at 600Mhz" safeguards?

[From: Igor.Stoppa at nokia.com]

Hi,
the damage is not directly related to the temperature, but rather to the overvoltage used @600MHz.

There are few temperature sensors, but not all of them are accessible to the normal SW and most are just thermal shutdown safeguards.

But the battery, for example, has a temperature sensor nearby.

However please notice that usually their readings are meaningless apart from indicating the _local_ temperature, since there are so many heat sources on the board.

Finally, being the device basically plastic, not perceiving high temperature at surface level is not so relevant, since plastic is not such a good thermal conductor and allows for higher and longer power peaks. Phones with metallic casing have lower max temperature allowed at surface level because of the higher transfer efficiency (the delta being 15C, on top of my head).

Cheers, Igor
________________________________________
From: maemo-developers-bounces at maemo.org [maemo-developers-bounces at maemo.org] On Behalf Of ext Matan Ziv-Av [matan at svgalib.org]
Sent: 28 January 2010 01:25
To: Javier S. Pedro
Cc: maemo-developers at maemo.org
Subject: Re: Where are the N900 "too much time at 600Mhz" safeguards?

On Wed, 27 Jan 2010, Javier S. Pedro wrote:

> When I got my N900, one of the first things I noticed is that (as measured by
> powertop) I could never get a 100% ratio at 600 Mhz, but more like 95%. I
> quickly assumed this was the safeguard for the issue Igor Stoppa talked about
> at the Maemo Summit.
>
> However, I've noticed today (as suggested by a tmo post) that the above is not
> caused by any special modification in the kernel, but rather because of the
> CPU idling while waiting for the SGX / some other hw (so, testing methodology
> failure on my part :) ).
>
> Thus, given any task bounded by raw CPU throughput, the device will happily
> clock itself at 600Mhz, even for hours. Doesn't that contradict what Igor said
> at the summit?


At least for 30 minutes, there appear to be no 'safeguards':

N900:~# date ; cat /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state ; for  i in ` seq 1 1000` ; do bzip2 -c9 /lib/libc-2.5.so  > /dev/null ; done ; cat /sys/devices/system/cpu/cpu0/cpufreq/stats/time_in_state ; date
Wed Jan 27 15:35:32 IST 2010
600000 43683
550000 487
500000 17132
250000 1164197
600000 254442
550000 487
500000 17132
250000 1164200
Wed Jan 27 16:10:39 IST 2010


This represents more than 99.99% of 35 minutes at 600MHz.

Note that I ran this test with no SIM, screen off, not charging and wifi
connected, but with practically no traffic. The device got only slightly
warm, but it was hardly noticeable, so I guess that the power draw of
the CPU, even at 600MHz does not have a large effect the system.

BTW, is there a temperature sensor somewhere in the system like there is
in the N810?

--
Matan Ziv-Av.                         matan at svgalib.org


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