A Conditional Scheduling Approach to Designing Real-Time Systems

Lloyd Greenwald and Thomas Dean

We present an approach to designing real-time systems based on dynamically sequencing condition-specific task-execution schedules. A system that dynamically alters its real-time execution component provides flexibility in the face of changing on-line conditions. For domains in which real-time response and safety must be guaranteed at design time, achieving this flexibility requires the introduction of new modeling and analysis tools. We provide analytical techniques for validating the behavior of a real-time system designed under our conditional scheduling approach. We demonstrate the approach through the detailed design and analysis of a real-time avionics scheduling solution. This solution involves architectural changes to existing avionics system hardware and makes use of predictive models of in-flight dynamics to provide real-time behavior guarantees at design time. The approach described in this paper is an example of the use of a general framework that we have developed for analyzing tradeoffs when designing systems in which an agent with limited computational resources is required to respond in a timely manner to situations arising in a dynamic environment.

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