Abstract: Rapid prototyping of complex systems embedded in even more complex environments raise the need of a multi-level design approach. Our example is taken from mechatronic design of the automotive industry and illustrate the rapid prototyping procedure of real-time critical control laws. Our approach is based on an object oriented structuring allowing not only central control units but supports distributed control units as needed in todays designs. The implementation of control laws is a stepwise refined hardware-in-the-loop simulation reducing the simulation part in each step. At the lower level common platforms as FPGAs, microcontrollers or specialised platforms can be instantiated. This is illustrated by an asynchronous data-flow processor for high performance rapid prototyping of cyclic iterated control laws.