One phone interview and one face-to-face. They paid airplane, taxi and hotel. They first sent me a simple problem to implement it (color convertion for 2-D image and blending). Then we talked on the phone for my background, optimizations on the piece of code I wrote. Face-to-face had 3 phases, each with a group of 2 people. First general C questions and a bit of hardware, second compiler stuff and third compiler specific optimizations. Not very difficult but I wasn't well prepared. Very relaxed guys, eager to answer every question about the company and even make a joke.