[maemo-developers] [maemo-developers] Re: Measuring power consumption of 770

[From: Igor Stoppa]

Hi,
On Sat, 2006-03-18 at 16:17 +0200, ext Teemu Nikkilä wrote:
> On Saturday, 18. March 2006 13:47, Claudio Scordino wrote:
> > > > If I can make the 770 work with only the battery charger (using a kind
> > > > of bypass instead of the battery), I could use my multimeter for
> > > > electrical sockets to measure the power consumption of the device...
> 
> In case you mean a simple kW/h meter, I doubt you will get any meaningful 
> results with one.
> 
> > > I repeat this only because you might have missed my previous advice.
> > > You DO want to use the battery, _without_ the charger.
> >
> > Actually I missed it...
> 
> If you missed the discussion, I suggest you check it out and possibly consult 
> someone who is into electronics and measurement technology and has access to 
> a reasonably well equipped lab.

I agree, I have to point out that the battery itself does a pretty good
job at pretending to be an ideal voltage source, therefore voltage
variations are very small across time and load variations.
And the current itself is not extremely high.

Therefore to measure _variations_ of power consumption and also to be
able to tell what part of the delta is due to custom "enahncements" and
what part is due to the standard power saving features (both HW and SW)
that the 770 alreay has, one needs to have a good understanding of both
the 770 internals and low power measurements in general.

Disabling the internal power saving features would render the experiment
meaningless, imho, because it would generate an unrealistic use case.

If dealing properly with this sort of device/measurement is not
possible, I would recommend to rather focus on a laptop: it has similar
problems but an architecture with far less advanced power saving
features, both HW and SW and also uses higher power levels, therefore
using a meter connected to the power lines is not totally unreasonable.

Dealing with Omap implies also having a good understanding of power
correlations between subsystems: arm, dsp, internal and external
peripherals and what the sw does to use such features.

> 
> I understand it is easier to do in software, though.
> 
> -Teemu
> 
> >
> > Many thanks again,
> >
> >               Claudio
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-- 
Cheers,
           Igor

Igor Stoppa (Nokia M - OSSO / Tampere)