Abstract
In order to reduce overestimations of worst-case execution time (WCET), in this article, we firstly report a kind of specific WCET overestimation caused by non-orthogonal nested loops. Then, we propose a novel correction approach which has three basic steps. The first step is to locate the worst-case execution path (WCEP) in the control flow graph and then map it onto source code. The second step is to identify non-orthogonal nested loops from the WCEP by means of an abstract syntax tree. The last step is to recursively calculate the WCET errors caused by the loose loop bound constraints, and then subtract the total errors from the overestimations. The novelty lies in the fact that the WCET correction is only conducted on the non-branching part of WCEP, thus avoiding potential safety risks caused by possible WCEP switches. Experimental results show that our approach reduces the specific WCET overestimation by an average of more than 82%, and 100% of corrected WCET is no less than the actual WCET. Thus, our approach is not only effective but also safe. It will help developers to design energy-efficient and safe real-time systems.
Highlights
Programs in a real-time systems should be executed as fast as possible
In order to obtain a tighter worst-case execution time (WCET) estimation, we propose a novel approach to reduce a kind of specific WCET overestimation
The last step is to recursively calculate the WCET errors caused by the loose loop bound constraints, and subtract the total errors from the overestimations
Summary
Programs in a real-time systems should be executed as fast as possible. The execution speed can severely affect the system’s energy consumption [1,2]. For a battery-powered real-time system, since the energy is limited, a tradeoff between energy consumption and execution time is necessary [3]. The precondition is that the execution time of all programs should meet the related deadline constraints. Otherwise it may lead to casualty, environmental damage, property loss and other disasters. In order to ensure safety, one primary task during designing such real-time systems is to accurately estimate the program’s worst-case execution time (WCET). WCET estimations are key parameters for the evaluation of software safety and the optimization of energy consumption
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