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.
Minor amends:
- bleDisconnectionCallback signature change
- bleSetAdvertisingInterval now takes milliseconds as a parameter
- event based invocation of DFU bootloader
- LFSR generated values in a subset of the range requested (rounded to the nearest lower power of 2).
Corrected by increasing the number of bits usedby one, such that it now generated st least the power of 2 greater.
- replaced enable/disable of interrupts with a local snapshot of randomValue. Much of the nordic software is sensitive to interrupt timings,
so best avoided where possible. Chance of race condition is low, and effect is minimal (duplicate number returned).
Uisng libc's implementation is likely to be safer than rolling our own. At least
the failure modes are well documented. (glibc's implementation of rand() is
actually not bad).
The LFSR used only provides 1 bit of random data each time it is cycled.
This implementation generates the minimum number of bits needed. Further
it discards numbers that are bigger than required and re-calculates -
this keeps the distribution flat.
Also recalibrated loop timers in MicroBitDisplay::Error(), as used by panic()...
strange these now seem off by several orders of magnitude.
TODO: Ensure CPU is running at correct internal frequency with an oscilloscope test...
Whilst a little more invasive change than the previous warnings
supression this is more correct and more obvious as to what's being done,
and what warnigns will remain in place for the rest of the comilation
unit.
Unfortunately we can't turn it off just while nrf_soc.h is being included
as the way the defines are used the compiler can't tell the parameters
are unused until the end of the compilation unit. So we can't use the
more normal
as that pops the supression too early.
WARNING: including nrf_soc.h will turn off unused-function warnings for
the rest of the compilation unit - see included nrf_svc.h
- Enures an event listener is not deleted whilst a fiber is activiely processing a queue
- Added support for resurrection of event listeners in cases where identical listeners are removed/added repetitively.
- Add maximum depth for event queues, to prevent buggy scripts causing total memory exhaustion.
- Suppress generation of A/B click events when A+B click is generated
- preservation of event ordering on messagebus for resursive event generation cases.
- bugfix of message bus processing to prevent occasional dual processing of events
- bugfix MicroBitDisplay to behave correctly when delay parameter is zero.
Joe Finney