[Community] GTA04 - Power management improvements

Dr. H. Nikolaus Schaller hns at goldelico.com
Fri Jan 17 11:32:07 CET 2014

Am 17.01.2014 um 10:56 schrieb Radek Polak:

> 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).

Yes, no doubt that it can be solved. With a handful of paid full-time engineers and with big budget.

For the GTA02 I am not sure if it was Openmoko, Inc. or the community.

> 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?).

Then your board must be broken, because we have made that sure 3 years ago... It was one of the first steps when bringing up the boards and testing if the components are the right ones.

All measurements I have done show

1/	~0mA
2/	between 3 and 100 mA (100mA temporarily if there is some communication with the base station) - this current depends heavily on antenna position and distance to base station

But I can test it again if you think it is not so.

2/ may be a higher if the IrDA module is installed. This is a well known problem of the GTA04A4 and will be fixed in A5.

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

It is less a problem finding a board but a person determined to solve the issues.

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