1. Except as otherwise indicated, orientation change happens once
the predicted rotation has been stable for 40ms. Noise is
suppressed by a low-pass filter with a 200ms time constant which
seems to be about as small as is practical given the quality
of the sensor data.
2. If the magnitude exceeds a threshold (excessive noise or freefall),
resets the predicted orientation.
Doesn't happen very often even when shaking the device.
This heuristic mainly protects the detector from spurious tilt due
to inaccurate determination of the gravity vector.
3. If the device was previously in a flat posture (on a table for at
least 1000ms), then it must move out of that posture for at least
500ms before the next orientation change will happen.
This heuristic suppresses most spurious rotations that happen while
picking up the device.
4. If the device is tilted away from the user by 20 degrees within
a span of 300ms, the device is said to be swinging and at least
300ms must elapse after the device stops swinging before the
next orientation change will happen.
This heuristic suppresses some but not all spurious rotations that
happen while putting down a device. Unfortunately, this heuristic
sometimes triggers a false positive when turning the device very
rapidly due to accelerometer noise. The 300ms pause is a compromise
so that occasional mispredicted swings don't significantly delay
the rotation.
Bug: 5796249
Change-Id: Id7b36c4c563e35b70d6a7ac36d04f3c3d6ea5811
5aa73ae58f