– Clocking is an essential component of any embedded system design. However, traditional design techniques are either short of clocking support or too complex for users. The Unified Modeling Language (UML) has been proposed as design tool in real time system design, but the clocking semantics has not been properly dealt with. In this paper, we will present our experience of using UML to design a clocked system. In particular, UML is used to model the digital down converter, an essential component of software radios. Our tool chain automatically generates the simulation as well as synthesizes the final implementation.