Now that the IMU is functioning, my next step is to use that to produce an attitude estimate.  Here, I dusted off my [unscented Kalman filter](http://unscented Kalman filter) based estimator from long ago, and adapted it slightly to run on an STM32.  As before, I used a UKF instead of the more traditional EKF not because of its superior filtering performance, but because of the flexibility it allows with the process and measurement functions.  Unlike the EKF, the UKF is purely numerical, so no derivation of Jacobians is necessary.  It turns out that even an STM32 has plenty of processing power to do this for things like a 7 state attitude filter.