Accelerometer question

[Joel Newkirk]

On Fri, 10 Oct 2008 01:01:14 +0100, Rui Miguel Silva Seabra <rms at 1407.org>
wrote:
> Hi,
> 
> Big question:
> 	Are the accelerometers constantly draining battery life?
> 
> 	or...
> 
> 	The rate at which they feed me data only starts up when the file
> 	handle is opened, and stops when it's closed?
> 
> If it's the first case, then the init scripts should shut both
> accelerometers down as soon as possible, and software that uses them
> should turn them on as needed.

AFAIK by default they're always powered up.  Certainly apart from the times
I hit 'dead accelerometers' that took a few reflashes to get going again,
I've never had to power them up unless I'd previously powered down.

According to the datasheet at http://wiki.openmoko.org/wiki/ST_LIS302DL:

Symbol Parameter Test         conditions         Min.Max.Unit
  Idd  Supply current         T = 25°C, ODR=100Hz 0.3 0.4 mA
IddPdn Current consumption in T = 25°C             1   5  μA
       power-down mode

So the power draw is pretty low, both together being less than one
milliamp.

I suspect that frameworkd will be able to shut them down automatically if
nothing needs them, once accel support is incorporated.  (IIRC it does that
now for other subsystems, like gps)

j