Accelerometer Data

Neil Brown neilb at
Mon Mar 23 06:36:23 CET 2009

On Sunday March 22, charles-henri.gros+openmoko at wrote:
> Iain B. Findleton wrote:
> > I have been playing a bit with the accelerometers on the FR appear to
> > observe the following:
> > 
> >    1) The time stamp on events appears to be unreliable, in the sense
> > that the time difference
> >        between sequential events is frequently negative, and appears
> > also to be have erratically
> >        by jumping an order of magnitude or 2 between sequentially
> > available events.
> > 
> >    2) It also appears to be relatively common that a SYN arrives before
> > all 3 axis values are available,
> >        making it hard to figure out the meaning of the data
> I've seen that too; it seems that '0' readings are discarded.

That is because the device reports REL events.
In the latest andy-tracking it reports the more correct 'ABS' events.
So now it does report zeros.  However it doesn't report an axis if there
has been no change.  If you want to simply get "the current values"
there is an ioctl : EVIOCGABS I think.


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