Worst-Case Execution Time Analysis of Disable Interrupt Regions in a Commercial Real-Time Operating System

Worst-Case Execution Time (WCET) analysis has been around for some time now, but has so far not been much used to analyse real production codes. Here, we present a case study where static WCET analysis was used to find upper time bounds for time-critical regions in a commercial real-time operating system. We report on practical experiences from the work, like the reverse engineering required to find these regions and prepare them for the analysis. We give the results of the WCET analysis and discuss the precision. We also present some qualitative and quantitative data on the program structure of the regions. This information is useful to judge whether WCET analysis could provide any useful results for this class of real codes, without excessive manual labour. Finally, we present a “wishlist” for features of WCET analysis tools, which has emerged during the project, and comment on the feasibility of implementing these features.