On the quantification of sustainability and extensibility of FlexRay schedules

FlexRay has emerged as the de-facto next generation in-vehicle communication protocol. Messages are scheduled incrementally on FlexRay according to the automotive design paradigm where new applications are added iteratively. On this account, the schedules must be (i) sustainable, i.e., when messages are added in later iterations, they must preserve deadline guarantees of existing messages and (ii) extensible, i.e., they must accommodate future messages without changes to existing schedules. Unfortunately, traditionally used metrics of sustainability and extensibility for timing and schedulability analysis are generic and can not be trivially adapted to FlexRay schedules. This is because of platform-specific properties of FlexRay like being a hybrid paradigm, where both time-triggered and event-triggered segments are used for communication. In this paper, we first introduce new notions of sustainability and extensibility for FlexRay that capture protocol-specific properties and then present novel metrics to quantify sustainable and extensible schedules. We demonstrate the applicability of our results with industrial-size case studies and show that our proposed metrics may be visually represented allowing easy interpretation by system designers in the automotive industry.