Simulation tools have been touted as a way to achieve improved quality and productivity in the design of automotive electrical and electronic dynamic systems. In most design environments, system interactions and integration can only be studied after the first development units have been built. One of the most complex interfaces is between hardware and software, which are usually developed independently. In this paper, we use the Saber® simulator to design and study system interactions in order to show how hardware/software development can be done simultaneously. In particular, we show how top-down design methods can be utilized to take a real life design from concept all the way to layout.