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Author SHA1 Message Date
Joe Finney d51b1205f7 microbit: Added support for compass tilt compensation
An e-compass solution requires knowwlede two pieces of data to provide an
accurate heading:

  - Accurate calibration of the magnetometer hardware so that reliable
    measurements can be taken.
  - Knowledge of the pitch and roll of of device, so that the correct
    components of the X/Y and Z axis sensors of the magnetomer can be used
    to sense the magnetic field in a horizontal plane regardless of the tilt
    of the device.

This commit represent changes to the MicroBitAccelerometer and MicroBitCompass
classes to implemen tthese goals. More specifically, this commit provides:

 - The introduciton of an interactive calibration 'game', that can rapidly
   gather all the data required to calibrate the compass.

 - An improved calibration algorithm based on a Least Mean Squares approach of
   compass samples, as documened in Freescale Application Note AN4248.

 - The inclusion of a simple Matrix4 class to enable efficient Least Mean
   Squares implementation.

 - A change from asynchronous to synchronous calibration of the compass when
   first used. This is in repsonse to a feature request for this from users
   and high level languages using microbit-dal.

 - Support for detemrining tilt and roll angle in MicroBitAccelerometer

 - Support for multiple co-ordinate spaces in MicroBitAccelerometer and
   MicroBitCompass. Data can now be read in either RAW (unaltered) data.
   MICORBIT_SIMPLE_CARTESIAN (as used previously) or NORTH_EAST_DOWN
   (the industry convention in mobile phones, tablets and aviation)

 - Implementation of a tilt compensated algorithm, used when determining
   device heading.
2016-01-09 00:20:19 +00:00