FlexRay will very likely become the de- IntroductionMany safety-critical applications, following physical, modularity or safety constraints, are implemented using distributed architectures composed of several different types of hardware units (called nodes), interconnected in a network. For such systems, the communication between functions implemented on different nodes has an important impact on the overall system properties, such as performance, cost and maintainability.There are several communication protocols for realtime networks. Among the protocols that have been proposed for in-vehicle communication, only the Controller Area Network (CAN) [4], the Local Interconnection Network (LIN) [17], and SAE's J1850 [30] are currently in use on a large scale [20]. Moreover, only a few of the proposed protocols are suitable for safety-critical applications where predictability is mandatory [29].Communication activities can be triggered either dynamically, in response to an event (event-driven), or statically, at predetermined moments in time (time-driven). Therefore, on one hand, there are protocols that schedule the messages statically based on the progression of time, such as the SAFEbus A large consortium of automotive manufacturers and suppliers has recently proposed a hybrid type of protocol, namely the FlexRay communication protocol [11]. FlexRay allows the sharing of the bus among event-driven (ET) and time-driven (TT) messages, thus offering the advantages of both worlds. FlexRay will very likely become the de-facto standard for in-vehicle communications. 1 However, before it can be successfully deployed in applications that require predictability, timing analysis techniques are necessary to provide bounds for the message communication times [20].FlexRay is composed of static (ST) and dynamic (DYN) segments, which are arranged to form a bus cycle that is repeated periodically. The ST segment is similar to TTP, and employs a generalized time-division multiple-access (GTDMA) scheme. The DYN segment of the FlexRay protocol is similar to Byteflight and uses a flexible TDMA (FTDMA) bus access scheme.Although [24], none of these analyses is applicable to the DYN segment in FlexRay. In [7], the authors consider the case of a hard real-time application implemented on a FlexRay bus. However, in their discussion they restrict themselves exclusively to the static segment, which means that, in fact, only the classical problem of communication scheduling over a TDMA bus [24,12] is considered. The performance analysis of the Byteflight protocol, which is similar to the DYN segment of FlexRay, is analyzed in [5]. The authors assume a very restrictive "quasi-TDMA" transmission scheme for time-critical messages, which basically means that the DYN segment would behave as an ST (TDMA) segment in order to guarantee timeliness.In this paper we present the first approach to timing analysis of applications communicating over a FlexRay bus, taking into consideration the specific aspects of this protocol, including the DYN ...

This paper deals with specific issues related to the design of distributed embedded systems implemented with mixed, eventtriggered and time-triggered tusk sets, which communicate over bus protocols consisting of both static and dynamic phases. Such systems are emerging as the new standard for automotive applications. We have developed a holistic timing analysis and scheduling approach for this category of systems. We have also identified several new design problems characteristic to such hybrid systems. An example related to bus access optimization in the context of a mixed static~dynamic bus protocol is presented. Experimental results prove the efficiency of such an optimization approach.

This paper deals with specific issues related to the design of distributed embedded systems implemented with mixed, event-triggered and time-triggered task sets, which communicate over bus protocols consisting of both static and dynamic phases. Such systems are emerging as a new standard for automotive applications. We have developed a holistic timing analysis and scheduling approach for this category of systems. Three alternative scheduling heuristics are presented and compared. We have also identified several new design problems characteristic to such hybrid systems. An example related to bus access optimization in the context of a mixed static/dynamic bus protocol is presented. Experimental results prove the efficiency of such an optimization approach.

An increasing number of real-time applications are today implemented using distributed heterogeneous architectures composed of interconnected networks of processors. The systems are heterogeneous not only in terms of hardware and software components, but also in terms of communication protocols and scheduling policies. In this context, the task of designing such systems is becoming increasingly difficult. The success of new adequate design methods depends on the availability of efficient analysis as well as optimization techniques. In this article, we present both analysis and optimization approaches for such heterogeneous distributed real-time embedded systems. More specifically, we discuss the schedulability analysis of hard real-time systems, highlighting particular aspects related to the heterogeneous and distributed nature of the applications. We also introduce several design optimization problems characteristic of this class of systems: mapping of functionality, the optimization of access to communication channel, and the assignment of scheduling policies to processes. Optimization heuristics aiming at producing a schedulable system with a given amount of resources are presented.

FlexRay will very likely become the de-