Commit graph

3 commits

Author SHA1 Message Date
Joe Finney 8756bbd103 WIP: Lower RAM footprint compass calibration
- moved to single precision floats
- optimised transpose/multiply operation
- optimisation of algorithm
2016-01-26 21:52:22 +00:00
Joe Finney 6916d506b8 microbit: Removed print funcitons from matrix class due to SRAM overhead of
native printf() call.

The Matrix4::print() function is useful, but non essential for most
applications, and the underlying printf() call required cost an
additional 1K of RAM on first use, which is currently above the budget for
micro:bit.
2016-01-09 10:25:26 +00:00
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