Developing safety-critical real-time systems with SDL design patterns and components

SDL is a system design language for the development of distributed systems, including real-time systems. In this paper, we apply SDL to capture design solutions found in safety-critical real-time systems. In particular, we present a methodology to augment system safety step-by-step, and systematically define and apply reusable design solutions for safety-critical real-time systems, expressed as SDL design patterns and components. These solutions can be added to real-time system designs, to protect against certain types of system failures. We illustrate the approach by the definition of reusable solutions for the detection of fail-silent nodes-a watchdog and a heartbeat-and their application to a distributed airship flight-control system.