On-line maintenance with on-the-fly software replacement

At Philips Research Laboratories Aachen we have found a way to reconfigure software in embedded systems like, for example, switches or set top boxes. The goal of the reconfiguration is to repair software faults and to update software functionality. This should be done on-the-fly without decreasing the system's availability which means during the on-going operation of the system. The developed approach is based on available distributed operating system technology (Chorus) and on a widely used family of programming languages (C/C++). It does not require changes in the operating system nor in the development system. All needed adaptations are done in the application. However, it was our goal to keep the development of the application functionality separated from the creation of the replaceability. An application is made replaceable through some systematic changes which can be done automatically. Some additional effort is still needed. This paper describes the mechanisms developed for that purpose. As a reconfiguration unit we have chosen a Chorus actor which is a kind of a multi-threaded process. We describe how to make such a process replaceable. Finally, we give some performance figures to show the efficiency of the implemented algorithms.