I've just installed my old APM/IMU/Magnetometer from my Arducopter into my Skywalker and installed the latest APM code.
During testing I found that the AH wasn't displaying heading, and I've checked the hardware setup screen and confirmed that compass is enabled with declination set.
I've then gone to CLI and tried to run compass test, and it reports that the compass of off.
I then goto setup and give the command compass on
It reports initialisation failed.
I'm sure it was working on my Arducopter.