[Gta04-owner] Modem off

NeilBrown neilb at suse.de
Thu Sep 19 03:47:47 CEST 2013

On Sun, 15 Sep 2013 08:29:37 +1000 NeilBrown <neilb at suse.de> wrote:

> On Sat, 14 Sep 2013 18:11:29 +0200 Radek Polak <psonek2 at seznam.cz> wrote:
> > Hi,
> > i wonder if modem powering off works as it should. Attached is charging graph 
> > taken from my GTA04.
> > 
> > You can see power consumption for:
> > 
> > 1/ normal suspend 13:09 to 14:26, discharging current is 24mA
> > 
> > 2/ suspend when modem was turned off as documented here [1] from 14:32 to 
> > 16:11, discharging current is 37mA
> > 
> > 3/ device turned off with modem turned off from 16:11 to 16:59, discharging 
> > current is 14mA
> > 
> > What is strange - i'd expect current at 2/ to be under 24mA and it should tell 
> > us how much modem eats.
> Clearly the modem actually generates current (harvested from the air waves)
> and when you turn it off, you no longer benefit from that :-)
> I've noticed this too.  I blame the USB interface.  I'm not really sure why,
> but my current theory is that is it the source of all our problems.

I have some more evidence.

I currently have ehci_hcd compiled as a module, so it needs to be loaded
before the modem can be seen.

On a fresh reboot of 3.7 without loading the module or toggling the GPIO to
turn on the 3G modem, I see a current draw during suspend of 21.6mA and 23.7mA
If I then "insmod ehci_hcd" the suspend-time current usage goes up to  30.1mA
and 32.2mA.
I then "rmmod ehci_hcd" and the current drops to 12.9 and 15.1 mA.

So in each case I see two different measurements with a 2.1mA difference.

Loading the module turns something on which was only partly one before.
Removing the module turns it off properly.

If I can get "suspend" to turn off whatever "rmmod" turns off, we might be
able to get power usage down by several milliAmps.

If anyone else would like to try this and report the results I would love to
hear them.
You need to set:


in .config and make sure nothing turns the modem on at boot time.
Then measure the suspend current.  Then insmod and measure it again.  Then
rmmod and measure it a third time.

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