Hi Helge,
I don't remember the reason why you didn't end up using the "normal" imu_aspirin_v2.1 subsystem/module (where the mag is a slave of the MPU)...
In any case with the conversion from subsystems to modules [1] we decided to not provide different defaults for LPC and STM based boards anymore, as that was causing quite a bit of confusion.
So now we only have one default (See
http://docs.paparazziuav.org/v5.10/module__imu_mpu6000_hmc5883.html), in that case the default IMU_MPU_SPI_SLAVE_IDX is now SPI_SLAVE0 for all boards (where formerly it was SPI_SLAVE2 only for STM boards).
And as SPI_SLAVE2 doesn't exist on all boards, SLAVE0 was a better default...
And you don't have to change the module xml file, you can configure it from your airframe file:
<module name="imu_mpu6000_hmc5883">
<configure name="IMU_MPU_SPI_SLAVE_IDX" value="SPI_SLAVE2"/>