Abstract

To guarantee timeliness in hard real-time systems the knowledge of the worst-case execution time (WCET) for its time-critical tasks is mandatory. Accurate and correct WCET analysis for modern processor is a quite complex problem. Path analysis is required to identify a minimal set of possible execution paths. Further, the modeling of a processor’s internal states for features like caches or pipelines requires to consider possible interferences of these features. Document type: Part of book or chapter of book

Abstract

Traditional Worst-Case Execution-Time (WCET) analysis is very complex. It has to deal with path analysis, to identify and describe the possible execution paths through the code to be analyzed, and it has to model the worst-case timing of the possible paths on the target hardware. The latter is again nontrivial due to interference of modern hardware features like instruction pipelines, caches, and parallel instruction-execution units on the processor. Document type: Part of book or chapter of book

Abstract

International audience; Long pipelines need good branch predictors to keep the pipeline running. Current branch predictors are optimized for the average case, which might not be a good fit for real-time systems and worst- case execution time analysis.This paper presents a time-predictable branch predictor co-designed with the associated worst-case execution time analysis. The branch predictor uses a fully-associative cache to track branch outcomes and destination addresses. The fully-associative cache avoids any false sharing of entries between branches. Therefore, we can analyze program scopes that contain a number of branches lower than or equal to the number of branches in the prediction table. Experimental results show that the worst-case execution time bounds of programs using the proposed predictor are lower than using static branch predictors at a moderate hardware cost.