DCW

Abstract

Real-time systems continuously interact with the physical environment and often have to satisfy stringent timing constraints imposed by their interactions. Those systems involve two main properties: reactivity and predictability. Reactivity allows the system to continuously react to a non-deterministic external environment, while predictability guarantees the deterministic execution of safety-critical parts of applications. However, with the increase in software complexity, traditional approaches to develop real-time systems make temporal behaviors difficult to infer, especially when the system is required to address non-deterministic aperiodic events from the physical environment. In this article, we propose a reactive and predictable programming framework, Distributed Clockwerk (DCW), for distributed real-time systems. DCW introduces the Servant, which is a non-preemptible execution entity, to implement periodic tasks based on the Logical Execution Time (LET) model. Furthermore, a joint schedule policy, based on the slack stealing algorithm, is proposed to efficiently address aperiodic events with no violated hard-time constraints. To further support predictable communication among distributed nodes, DCW implements the Time-Triggered Controller Area Network (TTCAN) to avoid collisions while accessing the shared communication medium. Moreover, a programming framework implements to provide a set of programming APIs for defining timing and functional behaviors of concurrent tasks. An example is further implemented to illustrate the DCW design flow. The evaluation results demonstrate that our proposal can improve both periodic and aperiodic reactivity compared with existing work, and the implemented DCW can also ensure the system predictability by achieving extremely low overheads.