Assessing Software Abstractions in WCET Analysis of Reactive Programs

The estimation of the worst case execution time (WCET) of a reactive system on agiven architecture is an important goal for time-critical systems. However, it cannotbe achieved exactly, because of the complexity of modern architectures, the undecidability of most program analysis problems, and the need of taking into accountthe actual environment in which the system is intended to work. As a consequence,two approaches are possible: extensively testing the system with realistic input scenarios (dynamic method) provides an under-approximation of the WCET, while aguaranteed over-approximation can be obtained by applying static analysis of software and hardware. Comparing the results of both approaches and reducing the gapbetween them is interesting to assess the quality of the static analysis, and to decidewhen further refinements are useless. In this paper, we propose a methodology anda combination of tools to assess the result of software static analysis in the case ofreactive programs. In order to permit a meaningful comparison, we perform a dynamic analysis using a cycle accurate simulator based on the same hardware modelas the one used for static analysis. Moreover, we use an existing quite sophisticatedframework to conduct the generation of reactive input scenarios, in order to trackthe worst case. This methodology and the use of associated tools is illustrated on asmall but realistic example