[Gta04-owner] GTA04 suspend power consumption

H. Nikolaus Schaller hns at goldelico.com
Fri Oct 30 19:18:19 CET 2015

I have aquired a thermographic camera and made some pictures of a running GTA04
(without case and battery connected through external cables so that it does not cover
the chips on the PCB). 

Here are some first findings and conclusions (which may be wrong):

running from battery:

USB charging:

suspended (power LED still on):

tps65950 during suspend:


chip placement to compare:

During operation it is visible that the TPS65950, the charging control FETs, the
CPU+PoP and the USB3322 are "hot spots".

During suspend it was really unexpected. The TPS65950 stays at around 30°C
(23°C surrounding temperature) which means quite some energy is "consumed".

And, it is visible that the chip has 4 "quadrants". Looking up the quadrants deeply
in the board layout and TI documentation (BGA ball assignment) makes me think
it is the VDD2 regulator which drives VDD_CORE of the OMAP3.

VDD_CORE drives all the peripherals, GPU and some other components of the 
OMAP3 SoC while VDD_MPU drives the Cortex A8 and 1V8 drives the DRAM.

What I don't exactly know is which power rail is driving the built-in DSP and camera
image signal processor.

So my first conclusion would be that the 25 mA beyond 3.7 optimization we still
see comes from a GPU or DSP that is not properly suspended or disabled.

Well, we have no drivers for that...

We don't have them on a 3.7 kernel either, but 3.7 might handle some minor
clock/enables/resets differently to get a better situation.

So this are first results. More experiments may be able to prove or disprove this
idea. But kernel developers may be able to build on this and better focus their
search for the missing bit.

If I find time, I can try to prepare (restore) an old µSD to boot 3.7 and do a
comparable experiment.


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