[Gta04-owner] Tracking down power 'leak'

Christ van Willegen cvwillegen at gmail.com
Wed Sep 4 10:39:58 CEST 2013

On Wed, Sep 4, 2013 at 10:28 AM, Dr. H. Nikolaus Schaller
<hns at goldelico.com> wrote:
> Hi,
> Instead of an Amperemeter it would be better to insert a 0.1 Ohm shunt
> resistor in the - (GND) line of the battery and connect an Oscilloscope.

That makes it easier to adjust the scale, and it probably won't blow up :-)

The A-meter I have at home goes to 2A without replugging (I have 20A
that needs re-plugging), so I _may_ be able to do this myself.

>> Also, would it be possible to build a minimal system that has either
>> USB or serial support (I don't have a serial cable, so I can't do this
>> at home...) and then connect to it and manually (using a simple C
>> program tugging registers left and right) toggling all the hardware to
>> the lowest power state possible. Then. when we are reasonably sure
>> that everything is off, we can measure power usage to have a baseline
>> figure.
> Hm. Unfortunately the OMAP is so complex that there is no minimal
> system allowing for this approach. The closest thing is to use U-Boot
> (which is a single-user, no built-in power management OS). But
> there we don't have protocol support to enable/disable some peripherals.

Could it support SSH via USB somehow, or is only serial possible?

Can we bit-bang our way into the peripherals?

>> In the real system, is there a way to catch the (kernel) calls that
>> turn off various devices so that they can be logged somewhere? That
>> would enable finding out which devices are still enabled in some way.
> Christoph has done yet another approach a while ago (I think he did report
> it somewhere): 1. send the device to suspend, 2. use a very sensitive
> infrared camera to detect those chips that still dissipate some mW.
> If I remember correctly it did point out only CPU+RAM.

That would be enough to get down to a few mA, so there must be power
dissipated somewhere else.

Also, I suspect that the battery I'm using now is old. At the moment
I'm russing QtMoko v56, which uses about 35mA. That would mean an
empty battery in about 34hrs. (at least, more than a day). But, I need
to re-charge every day, so my battery is probably less than 1200 mAh
by now.

I have 2 other batteries, perhaps I need to pop in another one to see
if that helps...

Christ van Willegen
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

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