[Gta04-owner] GTA04 power management.

NeilBrown neilb at suse.de
Sat Dec 24 06:10:02 CET 2011

 I've been playing with power management and have not achieved the results I
 had hoped for yet and am running out of ideas.  So I thought I would
 summarise were I am at in the hope that someone can say something helpful.

 I'm particularly looking at suspend-mode.  While runtime power management
 (turning the CPU on/off dynamically as needed and adjusting voltage) is
 attractive it can never save more power than full suspend, so suspend mode
 will show us the minimum power usage without turning the device off

 I'm current measuring about 8%/hour battery discharge while in suspend mode
 which corresponds to approximately 100mA current drain.  When the device is
 off I lose about  1%/hour which is around 10mA (the precision of these
 measurements isn't great so there is a lot of rounding here) which is
 presumably attributed to the OPTION GSM module (and matches what HNS said it
 would be).

 So that suggests around 90mA still being used by something else.

 I've turned off the power supplies for WIFI, BT, GPS antenna, sensors.
 I've turned off VDD1 and VDD2 to the CPU, and the various power supplies for
 USB and the battery charger (VINTANA, VINTDIG).  All the leds are off.

 All that should be left on are VDDIO aka 1V8, and REGEN aka 3v3.  It seems
 that these need to be on by design.

 With the GPS off (it is, I checked) and the LEDs off and none of the
 other peripherals enabled, 3V3 shouldn't be providing much current as
 discussed previously.  The only things of any significance I can see driven
 1V8 are:

  - The 26MHz clock.  This seems to be on all the time where I (naively)
    would have expected it to be enabled by the CLKEN output from the TWL4030.
    I assume there is a reason for that?  How much current does it use?

  - Some power to the CPU.  If I read it correctly it is only supplying
    - DDS - the display subsystem
    - POP-DDR and POP_FLASH - the Package on Package memory.

    I would expect the DDS to be off (not sure how to check yet) and the
    memory to be in self-refresh mode.

 Any guesses were that 90mA is going?  I would understand a 10mA draw, but
 90mA seems a bit steep for a sleeping device.

 BTW, only slightly related: it looks like it might be possible to get the
 power management chip to turn 1v8 and 3v3 off and back on again in response
 to warm-reset.  So possibly I could use that to get the GPS into a known
 state if I really need to.

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