Fundamental design problems of distributed systems for the hard-real-time environment

Software designed to function in a hard-real-time environment where strict timing constraints must be met often entails implicit assumptions about a programming language and the underlying system which supports it. Programs which are logically correct, i.e., they implement the intended algorithms, may not function correctly if their assumed timing characteristics of the software or if the expressible timing characteristics cannot be verified before run time. For distributed systems in particular, the software must be tailored to a myriad of implementation parameters, e.g., communication bandwidth, thus rendering subsequent modifications hazardous. Our research investigates the basic problems in automating the design and maintenance of hard real-time software. After examining the limitations of the traditional approach to real-time software design via process-based models, we shall provide a graph-based computation model which is more suitable for expressing the computation requirements of the real-time environment. This model is an extension of CONSORT (Control Structure Optimized for Real-Time), an experimental software design system which has been implemented to generate process control application programs from block diagram schemata. While our graph-based model is abstract, it can serve as a useful intermediate representation between textual requirements specifications and target application programs. Using the graph-based model, the complexity of the relevant resource allocation problems for meeting stringent timing constraints is investigated.