[Gta04-owner] 3.2-rc6-gta04 - another week, another rc.

Dr. H. Nikolaus Schaller hns at goldelico.com
Tue Dec 20 07:05:36 CET 2011

Hi Neil,

>> It will stay on all the time since it is part of the proper power on/off sequencing
>> scheme. There is a timing diagram in the TPS65950 and DM3730 data sheets.
>> So suspend has to take care that it switches all devices to low power mode
>> (e.g by activating RESET or sending some I2C commands). According to the
>> data sheets this is possible. So 3.3V remains active but the system draws some
>> 50 uA from the 3V3 rail. And the modem draws 3-10 mA from VBATT.
> OK.  So just to make this concrete - my reading of the schematics says that
> 3V3 is used for :
> P204 - The LCD controller. (TD28TTEC1)
>         The LCD can fairly clearly be turned off.


> D-AUX, D-PWR - The LEDS.  The controller itself is on 1V8 and presumably
>        cannot be turned off.
>        So turning all the leds off will remove any current drain here.

yes - unless you want to have one LED flashing to indicate a suspend state.
I think the average power drain is low if the duty cycle is e.g. 1:256

> U702 - The video-out amplifier.  This is controlled by GPIO23 so that is
>        easy to manage. 


> U901 - internal USB phy for WWAN.  GPIO174 on reset and stopping the clock
>        from the usb port on the processor should stop that using power.


> U1102 - level shifter for wifi chip.  Presumably when no data is flowing
>        it doesn't use significant power.

I think if the 3V3 side (VCCB) is powered down it will draw only leakage currents

> M1201 - GPS as already discussed
> U1401 - the FM transceiver.  Presumably you can tell it to power down
>         the RF bits over the I2B bus?

Yes, I think so

> U1501 - serial port driver which can be powered-down with GPIO13, though that
>         turns the IrDA on which is powered straight from the battery.
>         Does that mean one of these has to be on always?  I guess the serial
>         driver doesn't use much current?

Hm. The serial driver needs some current for the voltage converters. But is
in the uA range if Powered down.

Then, I have seen in the data sheet of the IrDA driver that it draws approx. 2mA
on the receiver if enabled. The transmitter will produce one 100us impulse
and then shut down.

So we have to choose between IrDA-Rx active and RS232 active.

I think we should change that for a future board layout and decode the
gta04_version in the kernel.

> U1801 - VGA drivers - currently not implemented.
> So yes, most things can be clearly turned "off" - nor sure about serial or FM
> though
>> It is also that the 1.8V is not shut down not keep DRAM alive. And to keep
>> the GPIO pins active that are looking for wakeup impulses. But one core
>> voltage is completely shut down (I think VDD2).
>> But I have no real experience with it. We may have to do some tests as soon
>> as suspend/wakeup works. We can suspend the CPU and check the power
>> consumption and try to find out which chips are not shut down.
>> I would e.g. suspect the TSC2007 driver. It could be sent to deep sleep
>> where it just monitors the touch screen and can generate a PENIRQ
>> wakeup if someone touches the screen. 
> I'm not sure I want the screen to be sensitive except when it is fully on.
> And I presume you cannot power much of the CPU down while the display is on??

You could power down the display ("screen saver") but still wake it up through
the touch. The touch itself does not draw current if not touched (high resistance).
And the TSC2007 has a special mode in which it does not do ADC conversions
but directly monitors the touch and drives the PENIRQ.

I am also not sure if this is a good feature. It is too easy to wake up the device
unintended e.g. if carried in a bag. Maybe, it could become some configuration
option and is off by default.


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