A Hierarchical Flexray Bus and Task Scheduler

Flexray is widely expected to be the next generation in-vehicle communication bus protocol that will satisfy high-determinism, high bandwidth and safety-critical automotive requirements. The deployment of Flexray into the automotive architecture will require a paradigm shift from a development process and tools perspective relative to the legacy CAN-based development process and tools. One of the key aspects of this shift is in the concept that task and bus message schedules are deterministically decided during design time. This paper provides a scheduling framework that would enable a designer to schedule systems in a hierarchical fashion based upon an iterative refinement concept. The idea is to iteratively refine the schedule from the top level application cycle down to the communication cycle definition and finally to include the TDMA slot definition. This approach is amenable to the decoupling of task from message scheduling and further to enable the decoupling of the top level schedule from the protocol detail. The concept has been implemented as a tool in Microsoft Excel using a List Scheduling optimization scheme. Initial results from a case study based upon an active safety subsystem indicate the advantages and disadvantages of this approach to scheduling.