Linux - Android power consumption in suspend

Linux - Android power consumption in suspend

[Guru Prasad]

Hi,

I'm currently trying to compare the overhead of running Android over
bare linux on the Nexus S.
Towards this, I've built a TINY_ANDROID image that I'm using to
compare against stock AOSP (4.1.1_r4).

I noticed a discrepancy in the power consumption while the phone is suspended.
stock AOSP consumes ~1.2mA when suspended, whereas TINY_ANDROID consumes ~9mA.

The one change that was made to stock AOSP was that it was set to
airplane mode which disables the radio.
Initially I believed that the TINY_ANDROID build still has the radio
turned on and this is leading to the increased current draw.

I then put together a quick hack of the samsung_modemctl driver
(drivers/misc/samsung_modemctl) where I replaced existing
IOCTL_MODEM_RESET with calls to
dpram_modem_pwroff(mc);
modem_off(mc);

I'm not sure if this is sufficient to ensure that the radio consumes
no power, but despite doing this, I notice that the device continues
to draw ~9mA.

>From my understanding, the Android platform automatically suspends (by
using echo mem >/sys/power/state I presume) when it sees that there
are no wakelocks of the SUSPEND type being held. If the user pushes
the power button, then I believe it forcibly releases wakelocks to try
and suspend (eventually).


Could someone shed some light on what I'm missing or doing incorrectly?


Thanks