Quantifying notions of extensibility in FlexRay schedule synthesis

FlexRay has now become a well-established in-vehicle communication bus at most original equipment manufacturers (OEMs) such as BMW, Audi, and GM. Given the increasing cost of verification and the high degree of crosslinking between components in automotive architectures, an incremental design process is commonly followed. In order to incorporate FlexRay-based designs in such a process, the resulting schedules must be extensible, that is: (i) when messages are added in later iterations, they must preserve deadline guarantees of already scheduled messages, and (ii) they must accommodate as many new messages as possible without changes to existing schedules. Apart from extensible scheduling having not received much attention so far, traditional metrics used for quantifying them cannot be trivially adapted to FlexRay schedules. This is because they do not exploit specific properties of the FlexRay protocol. In this article we, for the first time, introduce new notions of extensibility for FlexRay that capture all the protocol-specific properties. In particular, we focus on the dynamic segment of FlexRay and we present a number of metrics to quantify extensible schedules. Based on the introduced metrics, we propose strategies to synthesize extensible schedules and compare the results of different scheduling algorithms. We demonstrate the applicability of the results with industrial-size case studies and also show that the proposed metrics may also be visually represented, thereby allowing for easy interpretation.