Static Worst-Case Execution Time (WCET) analysis is a technique to derive upper bounds for the execution times of programs. Such bounds are crucial when designing and verifying real-time systems. A key component for statically deriving safe and tight WCET bounds is information on the possible program flow through the program. Such flow information can be provided manually by user annotations, or automatically by a flow analysis. To make WCET analysis as simple and safe as possible, it should preferably be automatically derived, with no or very limited user interaction.In this paper we present a method for deriving such flow information called abstract execution. This method can automatically calculate loop bounds, bounds for including nested loops, as well as many types of infeasible paths. Our evaluations show that it can calculate WCET estimates automatically, without any user annotations, for a range of benchmark programs, and that our techniques for nested loops and infeasible paths sometimes can give substantially better WCET estimates than using loop bounds analysis only.
In this article we give an overview of the Worst-Case Execution Time (WCET) analysis research performed by the WCET group of the ASTEC Competence Center at Uppsala University. The basis for this work is our modular architecture for a WCET tool, used b oth to identify the components of the overall WCET analysis problem, and as a starting point for the development of an industry strength WCET tool prototype. Within this framework we have proposed solutions to several key problems in WCET analysis, including representation and analysis of the control ow of programs, modeling of the behavior and timing of pipelines and other low-level timing aspects, integration of the control ow information and low-level timing to obtain a safe and tight WCET estimate, and validation of our tools and methods. We have focussed on the needs of embedded realtime systems in designing our tools and directing our research. Our long-term goal is to provide WCET analysis as a part of the standard tool chain for embedded development (together with compilers, debuggers, and simulators). This is substantially facilitated by our close cooperation with the embedded systems programming-tools vendor IAR Systems.
Abstract. A n umber of methods have been presented to calculate the worst case execution time (WCET) of real-time programs. However, to properly handle semantic dependencies, which in most cases is needed to reduce overestimation, all these methods require extra semantic information to be given by the programmer (manual annotations for paths, loops and recursion depth). To m a n ually derive these annotations is often di cult and the process is error-prone. In this paper we present a new method to automatically derive safe and tight annotations for paths and loops. We illustrate our method by giving some examples and by presenting a prototype tool, implementing the method for a subset of C.
Abstract. Methods for Worst-Case Execution Time (WCET) analysis have been known for some time, and recently commercial tools have emerged. This technique is gradually being entered into industry to analyse real production codes. This article presents a case study where the aiT WCET analysis tool was used to find upper time bounds for taskoriented vehicular control code. The main purpose was to investigate the practical difficulties that arise when applying the current WCET analysis methods to this particular kind of code. In particular, we were interested in how labor-intense the analysis becomes, measured by the number of manual annotations necessary for calculating a WCET estimate. We were also interested how much tighter WCET estimates will become by manually adding extra annotations, and how much additional work that is needed to give these annotations. We also made some systematic comparisons between calculated and measured WCET estimates for the analysed system.
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