Power management concept...

Nils Faerber nils.faerber at kernelconcepts.de
Tue Apr 24 14:33:07 CEST 2007

Ian Stirling schrieb:
> Nils Faerber wrote:
> <snip>
>> Personally I would be much more interested in slow-mode than in
>> suspend/power-off. As I described it would allow (slow) applications
>> running all the time without much power consumption. This would be a
>> very interesting feature.
> Annoying things about slow mode.
> Uses several (3-5) times more power per MIP than fast mode.
> USB does not work, so no bluetooth.
> LCD controller does not work, so no display (unless as I've speculated,
> the LCD - as some can, can be written from the SPI bus).
> CPU alone in slow mode uses some 1/3 of the battery per day.

Oh, that's not good.
I hoped for something like the Nokia devices.

> Things that are possible - GPS, GSM, audio in/out (though there is not
> enough CPU to decode OGG/MP3/...).

And touchscreen I guess.

> It may well in many applications be better to - if it can be done
> rapidly - suspend to RAM for 5 seconds and wakeup for 1 second, in fast
> mode, repeatedly, rather than sitting in slow mode.
> This probably uses less power, and you can use the bluetooth module when
> you are awake.

Hmm... I can remember the older iPaq devices to do "short" wakeups for
checking battery state while charging. In this case the device did not
resume completely but only wake-up the CPU and SDRAM to check some
states and go to sleep again immediately afterwards.

Then this is probably a better approach if the slow mode consumes that
much power...

  nils faerber

kernel concepts GbR        Tel: +49-271-771091-12
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