Writing temporally predictable code

The Worst-Case Execution-Time Analysis (WCET Analysis) of program code for modern processors is a highly complex tasks: First, it involves path analysis, to identify and describe the possible execution paths through the code. Second, it models the worst-case timing of possible paths on the target hardware, where the characterization of the timing of sophisticated hardware features (e.g., instruction pipelines, caches, parallel execution units) and their interferences are non-trivial. This paper presents a programming paradigm that takes the complexity from WCET analysis. Program code written according to this paradigm only has a single execution path. Writing single-path code makes path analysis and thus WCET analysis trivial. The WCET of the single path is obtained by executing the code (necessarily on that single path) and logging the duration of this execution. To demonstrate that the single-path approach provides a universal solution to the WCET-analysis problem, the paper shows how every, WCET-analyzable piece of code can be translated into single-path code.

1 Introduction

Knowing the worst-case execution time (WCET) of tasks is crucial for building real-time systems. Only if safe WCET bounds for all time-critical tasks of a real-time system have been established can the correct timely operation of the whole real-time computer system be verified. During the last decade many research groups have undertaken research on (static) WCET analysis of real-time tasks and many sub-problems of WCET analysis have been solved [9].