[Community] GTA04 - Power management improvements

Radek Polak psonek2 at seznam.cz
Fri Jan 17 10:56:50 CET 2014


On Friday, January 17, 2014 09:57:55 AM Dr. H. Nikolaus Schaller wrote:

> > I'm still very suspicious of the internal USB driver which is documented
> > as now allowing the OMAP3 to go to sleep properly....
> 
> Yes, that might indeed be a key issue. But if it is the USB-PHY interface
> or the EHCI within the OMAP3 SoC we can't measure anything and cut any
> wire (on silicon).
> 
> One more thought why this issue is so difficult to work on. Because it
> needs a reproducible setup to compare different things. This starts with a
> controlled hardware setup, network coverage (because the modem may draw
> 100mA even if the CPU is off when trying to answer the base station),
> software setup.
> 
> And, such experiments need a lot of time. E.g. compile new kernels to try
> something. Flash a new SD card. Reboot. Then start measurements and
> compare results.
> 
> The results may be difficult to interpret, so the person doing this
> research has to study manuals, read web postings, and must get a 100%
> understanding of the interworkings.
> 
> This asks for a very big table, a test object GTA04 (not used for anything
> else every day) and a separate computer to control measurements and kernel
> variants. And an operator who can work on just this topic without major
> interruptions.
> 
> Even then it may take weeks to get to the 100%  understanding.
> 
> This is how big design labs like Nokia worked to develop the N900.
> 
> IMHO this is comparable with scientific research, trying to answer
> challenging questions: * "Why do neutrinos oscillate?"
> * "Why does it not go down below 10 mA in suspend"
> 
> You alternately build theories, try to verify/falsify by experiments and
> improve your theory until you can say: "we have to do this and that to
> make it better".
> 
> And you need some luck. Sometimes by doing the wrong experiment.

Yes it seems like difficult problem, but Openmoko, Nokia and every phone maker 
has managed to at least partially solve this (GTA02 has ~6mA in suspend, N900 
even less).

I have no electrical skills, but i'd make sure:

1/ when device is off it eats ~0 mA
2/ with just modem turned on ~3 mA

IIRC the values for 1/ and 2/ are currently very strange (somewhere around 
20mA?).

Btw i can provide my first GTA04 board for testing if needed - i have no use 
for it.

BR

Radek
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