One of the important aspects of schedulability analysis is the model used to describe the system and its timing behavior. On one side, the accuracy of the test strongly depends on the accuracy of the model. On the other side, a detailed model could lead to an inaccaptable evaluation time. In this paper we propose a new model, the hierarchical event streams, which allows a high accuracy. We provide an efficient feasibility test for the model based on the context of demand and request bound function. Additionally we will provide a methodology to extract this model out of a control-flow graph efficiently. Together this allows a more accurate and efficient schedulability analysis of event driven real-time systems.
Analyzing future distributed real-time systems, automotive and avionic systems, is requiring compositional hard real-time analysis techniques. Well known established techniques as SymTA/S and the real-time calculus are candidates solving the mentioned problem. However both techniques use quite simple event models. SymTA/S is based on discrete events the real-time calculus on continuous functions. Such simple models has been choosen because of the computational complexity of the considered mathematical operations required for real-time analysis. Advances in approximation techniques are allowing the consideration of more expressive descriptions of events. In this paper such a new expressive event model and its analysis algorithm are described. It integrates the models of both techniques. It is also possible in this module to integrate an approximative real-time analysis into the event model. This allows to propagate the approximation through the analysis of a distributed system leading to a much more efficient analysis.
The performance of feasibility tests is crucial in many applications. When using feasibility tests online only a limited amount of analysis time is available. Run-time efficiency is also needed for testing the feasibility of many different task sets, which is the case in system synthesis tools. We propose a fast uni-processor feasibility test using static priorities. The idea is to use approximation with a variable error to achieve a high performance exact test. It generally outperforms the existing tests which we show using a large number of random task sets.
In this paper we present a real-time analysis for complex distributed systems. The event stream model describes the occurrences of events within arbitrary time intervals. We propose a method to explore the modification of these occurrences as the events are processed within a complex task system. By observing the effects of several tasks competing for the same resource, additional insight can be won on the density of the events generated by the individual tasks.
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