Hierarchical Composition of Parametric WCET in a Component Based Approach

Worst Case Execution Time (WCET) computation is crucial to the overall timing analysis of real-time embedded systems. Facing the ever increasing complexity of such systems, techniques dedicated to WCET analysis can take advantage of Component Based Software Engineering (CBSE) by decomposing a difficult problem into smaller pieces, easier to analyse. To achieve this objective, the corresponding analysis results have to be composed to provide timing guarantees on the whole system. In this paper, we express the WCET of a component as a formula, allowing to represent its different computational modes. We then propose a Model Driven Engineering (MDE) approach that derives parametric WCET for composite components from parametric WCET of their subcomponents. This approach gives more accurate WCET estimates than naaive additive compositional analysis by taking into account usage context of components. However, analysis scalability concerns lead us to consider a trade-off between precision and scalability. This trade-off can be specified in the model. The composition of WCET estimations is automated and produces the parametric WCET expression of the composite component under analysis. This approach has been integrated in PRIDE.