Power leakage: save 40mW by turning GSM on

[Rask Ingemann Lambertsen]

On Sun, Jan 18, 2009 at 08:15:26PM +0000, Andy Green wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Somebody in the thread at some point said:
>
> |    After a reboot and turning off wifi, leaving BT, GPS, and GSM off,
> I get:
>
> Why do we think they're "off"?  As in, what actual action did you take
> that claimed to turn them off?

   I'm going by the indications of openmoko-panel-plugin. The initial state
when openmoko-panel-plugin starts is BT off, GPS off, WiFi on and GSM off. I
clicked on the WiFi icon and clicked "Turn WiFi off" in the popup menu to
turn WiFi off.

   I'm unable to measure any difference in power consumption between WiFi on
and WiFi off. In the list archives, I see there has been much discussion
about WiFi power management. It appears that you can't really turn off WiFi
power.

   Playing with the openmoko-panel-plugin gives:

   BT on increases current draw by 7,5 mA @ 3,79 V.
   GPS on increases current draw by 47 mA @ 3,79 V.

   For both BT and GPS, current draw reduces to the previous level by
turning off the device through openmoko-panel-plugin. On to GSM:

   GSM on increases current draw by 2,2 mA @ 3,80 V.
   Now comes the surprice:
   GSM off further increases current draw by 17 mA @ 3,80 V. :-(
   GSM on now _decreases_ current draw by 17 mA @ 3,80 V.

   I reboot with 'shutdown -r now', hold AUX to get into NOR u-boot and boot
from SD-card. That also recovers the 2,2 mA initially drawn by GSM.

-- 
Rask Ingemann Lambertsen
Danish law requires addresses in e-mail to be logged and stored for a year