Probabilistic scheduling of the FlexRay dynamic segment

Abstract

FlexRay is a communication system for automotive applications with high determinism, bandwidth, synchronization and reliability requirements, being a de facto standard for intra-vehicular communications in high-end vehicles. FlexRay media access control is based on a fixed-size communication cycle structured as a sequence of four segments: a Static Segment, a Dynamic Segment and two control segments. While the Static Segment is mainly used for transmissions related to time-triggered applications with hard real-time constraints, the Dynamic Segment is designed to accommodate transmissions from event-triggered applications with hard or soft real-time constraints, or from applications without real-time constraints. Some research works do consider a system model where message streams are sporadic with hard real-time constraints. To the best of our knowledge, there isn't in the literature research works addressing specifically the problems related to the transmission of messages from aperiodic streams in DN. In this work, we are proposing an arbitration mechanism to schedule aperiodic message streams on DN that avoids the indefinite postponement of low-priority streams. The proposed mechanism uses a probabilistic approach that takes advantage of the flexibility of aperiodic message streams regarding real-time constraints.