Timing Analysis of the FlexRay Communication Protocol

Abstract

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 ...

Categorizing and Analysis of Activated Faults in the FlexRay Communication Controller Registers

“…It has been reported that the overall reliability of a safety-critical distributed embedded system not only depends on the reliability of its nodes, but also more on the reliability of its communication network [1], [2]. This means that if a communication network fails, the overall operation cannot be succeeded; however, if a node fails, its task can be assigned to another node.…”

“…To resolve the drawbacks of both event-triggered and time-triggered protocols, other protocols such as TTCAN, FTT-CAN, and FlexRay [4] are introduced. Among the latter protocols, the FlexRay protocol is advancing as the predominant protocol and is expecting to become the de-facto industry standard for X-by-wire applications [5], [2], [3], [6]. As an example, the next edition of the BMW X5 will use the FlexRay protocol in its electronically controlled dampers [5].…”

Model Checking the FlexRay Startup Phase

“…Their analysis is however of a rather different kind, as they provide a schedulability analysis based on a correctly working protocol [21]. Such results can be extremely useful in proving correctness of a distributed application, as it may guarantee thatunder given circumstances-data will travel through the system.…”

Assessment of Message Missing Failures in FlexRay-Based Networks

“…Examples of timetriggered protocols are the SAFEbus, SPIDER, and Time-Triggered Protocol (TTP). The main drawback of the time-triggered protocols is their lack of flexibility [2]. Examples of event-triggered protocols are the Byteflight introduced by BMW Company for automotive applications, CAN, LonWorks and Profibus.…”

“…The FlexRay allows the sharing of the bus among event-triggered and time-triggered messages, thus offering the advantages of both protocols. It is reported that the FlexRay will very likely become the de-facto standard for in-vehicle communications [2] [4]. The FlexRay defines a communication cycle (bus cycle) as the combination of a time-triggered (or static) window, an event-triggered (or dynamic) window, a symbol window and a network idle time (NIT) window.…”