Cyber-physical systems (CPSs) include time-critical embedded systems where strict timing constraints are considered. These specific CPSs are dealing with close loop control functions, they are interfacing to sensors and actuators and have to fulfill safety critical real-time constraints. To guarantee the timing correctness, a lot of work introduced the strict-periodicity constraint. The latter is of great importance since it concerns sensors/actuators periodic tasks for which the relevancy of information they use is linked to the accuracy of their repetition. Applied to real-time control systems, the strict-periodicity constraint ensures much more stability and robustness. Therefore, the problem of scheduling real-time strictly periodic tasks has been targeted by several works in the literature but all these works were interested in nonpreemptive systems. In this work, we consider as strictly periodic and nonpreemptive only the sensory subtask and the remaining portion of the task may be preempted. This way, input transaction of every task receives the highest priority when accessing processor resource which enhances system predictability. On the other hand, the preemption allows easing schedulability analysis and, most of the time, it leads to a better processor utilization. The article proposes an optimal such task scheduling algorithm, called SPF for Strictly Periodic First, based on the Least Laxity First (LLF) scheduler and an efficient schedulability analysis. Simulation experiments with randomly generated task sets allowed showing the effectiveness of the proposed approach.

中文翻译：

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严格周期优先：LLF 的最佳变体，用于在时间关键的网络物理系统中调度任务

网络物理系统 (CPS) 包括时间要求严格的嵌入式系统，其中考虑了严格的时序约束。这些特定的 CPS 处理闭环控制功能，它们与传感器和执行器连接，并且必须满足安全关键的实时约束。为了保证时序的正确性，很多工作都引入了严格的周期性约束。后者非常重要，因为它涉及传感器/执行器的周期性任务，它们使用的信息的相关性与其重复的准确性相关联。应用于实时控制系统，严格的周期性约束确保了更高的稳定性和鲁棒性。所以，调度实时严格周期性任务的问题已成为文献中的几项工作的目标，但所有这些工作都对非抢占系统感兴趣。在这项工作中，我们认为只有感官子任务是严格周期性和非抢占式的，并且任务的剩余部分可能会被抢占。这样，每个任务的输入事务在访问处理器资源时获得最高优先级，从而增强了系统的可预测性。另一方面，抢占可以简化可调度性分析，并且在大多数情况下，它会导致更好的处理器利用率。本文基于最小松弛优先 (LLF) 调度器和有效的可调度性分析，提出了一种优化的此类任务调度算法，称为 SPF for Strictly Periodic First。