Developing predictable and flexible distributed real-time systems

Predictability is considered the most distinguishing characteristic of real-time systems. Besides that, adaptability is also a very important attribute because RT systems are usually designed for long life cycles, during which they will have to cope with change. This paper presents the STER real-time software development environment, designed to support the production of predictable, and yet flexible, distributed real-time systems. Flexibility is one of the main concerns of STER's programming model, based on the construction of reusable software modules. Modules can be reused with different timing constraints without having to be recoded, since the specification of their timing constraints is decoupled from their implementation. Predictable temporal behavior is obtained by an integrated allocation and scheduling strategy that involves off-line and online schedulers. The off-line scheduler tries to satisfy timing, precedence and allocation constraints of periodic hard real-time tasks, and to give the necessary leeway for the dynamic scheduling of aperiodic tasks. The paper shows how distributed programs are translated to scheduling graphs, and gives the results of some experiments conducted to evaluate the performance of the off-line algorithm