[maemo-users] brightness Re: [maemo-users] Re: Storage/Sleep Issues..

From: Igor Stoppa igor.stoppa at nokia.com
Date: Thu Jan 25 14:38:18 EET 2007
On Thu, 2007-01-25 at 13:08 +0100, ext Frantisek Dufka wrote:
> Igor Stoppa wrote:
> >> I thought it can be half of power 
> >> consumption on such devices. It was like that on ipaq 3870 I had. I 
> >> remeber something like 80mA when display off ~130mA minimum brightness 
> >> ~200mA full brightness, ~300mA full brightness + 100%CPU (not sure about 
> >> exact values, it is long time ago, it was available as file in /proc in 
> >> Familiar linux). On N770 I cannot check easily since some parts of power 
> >> management is ... guess what? There is this myth about hidden power 
> >> management ;-)
> > Nothinig prevents you from creating a sysfs entry wich returns 
> > 
> > tahvo_get_backlight_level()
> > 
> > or even a proc one, if you really are into that sort of thing.
> There is such entry - /sys/devices/platform/omapfb/panel/backlight_level
> I meant way to get discharge current from battery circuit to know what 
> is actual consumption of the device and how big is the influence of 
> various parts. This is easy to get on laptops and it was possible on 
> iPAQ but is currently kept very close to Nokia's chest.

I think you won't see this information made available anytime soon for a
very good reason: there is a significant risk that somebody uses this
knowledge to write malicious software that literally blows the device by
doing nasty thinigs with the battery and Nokia would be liable if it was
releasing such information. This is also behind the clause about reverse

One has to prove that we made it hard for him to get such information,
so that we are not liable when he blows hiimself up with a modified

>  Yes one can 
> measure it but it would need some tools, reading some register is much 
> easier. Would be also good guide for programmers implementing proper 
> idle state.
We are tryinig to figure out something similar, without risk.
But your statement is mostly for kernel side. Applications can use the
methods already described.

> I would be interested in difference betwen SD/MMC vs internal flash I/O 
> (i.e. how does rootfs on MMC affect battery life) but other things are 
> equally interesting to know (wlan transmit/receive, sound, DSP on, DSP 
> vs main CPU doing similar stuff ...).

It requires a little hw hacking, but you can measure them quite easily
with a good enough power meter (precise to mA) and some wiring.

Cheers, Igor

Igor Stoppa <igor.stoppa at nokia.com>
(Nokia M - OSSO /Helsinki Finland)

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