Firmware for the stm32f3discovery board which exposes its sensors through a
virtual serial port. It just combines several examples for libopencm3 into
one program. Different sensors are read by sending a different command to the
searial port: m for magnetometer, a for accelerometer, etc.
To build and flash the firmware:
$ git submodule init
$ git submodule update
$ cd firmware/libopencm3
$ make
$ cd ..
$ make
$ make flash
There is a sample application for a compass in the host folder.
You can see it in action here: https://www.youtube.com/watch?v=qPO57GnuQYc