The ?Distributed Control Lab? [6] at Hasso-Plattner-Institute, University of Potsdam allows experimentation with a variety of physical equipment via the web (intra and internet), among them the Lego Mindstorm robots and Foucault?s Pendulum. In order to conduct control experiments, students may write programs, which are validated, run on a simulator, and eventually downloaded on the actual control device. We use online replacement of software components (dynamic re-configuration) as a safeguard mechanism to avoid damage to our hardware.

Our research focuses on the extension of middleware concepts to embedded devices. The component-based architecture of the laboratory in conjunction with given timing and safety constraints dictated by the experiments make our infrastructure an ideal candidate for studying system predictability, availability and security in context of middleware-based dynamic control systems. Within this paper we are going to describe our extensible architecture for hosting physical control experiments and focus on Foucault?s Pendulum as a case study. For the Pendulum we have implemented a dynamic recon.guration algorithm, which is able to replace erroneous user-supplied control programs with a verified safety controller at runtime. In addition we are going to discuss the design of custom-built controller hardware which allows us to meet the timing constraints of the Pendulum experiment with a commercial-off-the-shelf (COTS) operating system and middleware. Architectural characteristics of our hardware and software as well as a performance evaluation of the recon.guration process will be discussed in some detail.