Analyzing Real Time Communication Over FlexRay

Abstract

In this paper we present an approach to timing analysis of applications communicating over a FlexRay bus, taking into consideration the specific aspects of the publish subscribe paradigm. We give an overview of works dealing with Data Distribution Service (DDS), scheduling over FlexRay and scheduling over the Control area Network (CAN). We are interesting in real time Quality of Service (QoS) for DDS. We specially focus on real time communication on static and dynamic FlexRay bus. We give our approach to calculate deadline on a DDS distribution using the equal Flexibility. We give also DDS and the task models for the computation. In Many distributed embedded real-time applications, like military, automobile, aeronautique data produced in one component of the system needs to be shared with other components of the system. The middleware Data Distribution Service DDS is divided into two components: the Data-Centric Publish-Subscribe DCPS layerand the Data local Reconstruction Layer DLRL. The DCPS layer transports data from publishers to subscribers according to Quality of Service QoS constraints associated with the data topic, publisher, and subscriber. The DLRL allows distributed data to be shared by local objects located remotely from each other as if the data is local. The DLRL is built on top of the DCPS layer. DDS impose of Service in transmission between publishers and subscribers. The transmission of data is managed by the real time bus. Real time applications use CAN or FlexRay bus. The challenge is to deal with a configuration using DDS middleware over FlexRay bus. The goal of using QoS in DDS is that all DataReaders read temporally valid data. DDS proveides QosPolicies specifically targeted to minimum latency, predictable real-time operation in high performance distributed data-critical systems. The DEADLINE QosPolicy expresses the maximum duration within which a DataReader expects a data-object instance to be updated. Our research team was interested in the LifeSpan (LS) Qos which concerns the Topic and the Data Writer entities. It specifies the maximum duration of validity of the data written by the DataWriter. They developed [6] an algorithm that calculate data distribution deadline. The following assumptions are considered: all nodes, data objects, and scheduling parameters are known a priori; each DataReader/DataWriter has a local node, where it originates.; the period of a DataWriter is always less than its Lifespan; and the offered deadline period is always less then the requested deadline period. This work gives an analysis for deadline computation on a FlexRay bus. The goal is to consider the data-centric publish- subscribe (DCPS) and to use DDS Qos. Both Dynamic segment and static segment are considered. We are currently working on a project to implement deadline computation with C language in order to finalize our works dealing with our DDS implementation.