Peter and I have discovered an odd behaviour with the lsm303d mag. If
you fetch data a bit too soon then it will give a peridic oscillation
in the output.
Checking the data ready bit in the status register doesn't help. The
only fix I've found is to run the sampling at a bit lower rate
Initialization was also changed a little bit so we don't try to
initialize 25 times. We rather use the same methods as in the
AP_InertialSensor drivers.
Also move up the call to is_zero() in read_raw so we don't set
_mag_[x|y|z] in case of failure.
These are not used. The only place where raw fields are used are in the
compass calibrator and we don't need to store them.
Additionally remove duplicated documentation about the meaning of the
functions to avoid them getting out of sync.
Not having data ready during initialization is normal. Don't print error
message since it can mislead people to think the compass was not
initialized successfully.
The PSTR is already define as a NOP for all supported platforms. It's
only needed for AVR so here we remove all the uses throughout the
codebase.
This was automated with a simple python script so it also converts
places which spans to multiple lines, removing the matching parentheses.
AVR-specific places were not changed.