the previous approach assumed a 1:1 mapping between compass backends
and compass instances, which isn't true on PX4.
It also only setup milligauss offsets on a set_and_save call, which is
not the only way offsets change
this adds a milligauss_ratio per instance, which is considerably
simpler
From now on there's a pair get_field_milligauss() and
get_offsets_milligauss() that can make the transition to the common
units across all compasses easier.
a saturated compass is now marked unhealthy, rather than causing the
code to spin waiting for a valid sample. This fixes a problem with
strong magnets causing the main flight loop to stop
Andrew Tridgell
Staroselskii Georgii
Víctor Mayoral Vilches
Randy Mackay
Andrew Tridgell