Algorithms for Infeasible Path Calculation

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. One key component in static WCET analysis is to derive flow information, such as loop bounds and infeasible paths for the analysed program. Such flow information can be provided as either as annotations by the user, can be automatically calculated by a flow analysis, or by a combination of both. To make the analysis as simple, automatic and safe as possible, this flow information should be calculated automatically with no or very limited user interaction. In this paper we present three novel algorithms to calculate infeasible paths. The algorithms are all designed to be simple and efficient, both in terms of generated flow facts and in analysis running time. The algorithms have been implemented and tested for a set of WCET benchmarks programs

Comparing WCET and Resource Demands of Trigonometric Functions Implemented as Iterative Calculations vs. Table-Lookup

Trigonometric functions are often needed in embedded real-time software. To fulfill concrete resource demands, different implementation strategies of trigonometric functions are possible. In this paper we analyze the resource demands of iterative calculations compared to other implementation strategies, using the trigonometric functions as a case study. By analyzing the worst-case execution time (WCET) of the different calculation techniques of trigonometric functions we got the surprising result that the WCET of iterative calculations is quite competitive to alternative calculation techniques, while their economics on memory demand is far superior. Finally, a discussion of the general applicability of the obtained results is given as a design guide for embedded software

History-based Schemes and Implicit Path Enumeration

The Implicit Path Enumeration Technique is often used to compute the WCET of control-intensive programs. This method does not consider execution paths as ordered sequences of basic blocks but instead as lists of basic blocks with their respective execution counts. This way of describing an execution path is adequate to compute its execution time, provided that safe individual WCETs for the blocks are known. Recently, a model for branch prediction has been integrated into WCET computation with IPET. This model generates safe estimations of the branch misprediction counts. However, we show in this paper that these counts can be over-estimated because IPET does consider simplified flow information that do not completely reflect the program semantics. We show how additional information on nested loops can be specified so that the model provides tighter WCET estimations