Worst–Case Execution Time Analysis Approach for Safety–Critical Airborne Software

Abstract

The fundamental problem in building a system with hard real–time characteristics is guaranteeing that it will deterministically perform its required functionality within specified time constraints. Determining Worst–Case Execution Time (WCET) is key to predictability, that is to ensure that temporal behaviour of the system is correct and hence safe. Furthermore, it is an objective to meet by verification when development of airborne software shall be compliant with DO–178B objectives. Different approaches to WCET analysis could be taken. This paper presents the experience automating such analysis for a Fly–By–Wire system by means of a hybrid approach aiming to combine features of measurement and static analysis. Several challenges arise when integrating the analysis workflow withing the software development process, especially those regarding to instrumentation overhead. Control mechanisms need to be developed to mitigate the drawbacks and achieve realistic WCET estimations to assess temporal correctness of the system.