FlexRay and its Applications

Real Time Multiplexed Network

Dominique Paret

• Publisher: Wiley
• Year: 2012
• ISBN:
  9781119966944
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Microelectronics
• Index: Technology & Engineering

An authoritative yet highly accessible guide to the design and operation of the FlexRay bus, the latest protocol for automotive network communications

A translation of the French edition, originally published in January 2011, this work is the result of numerous training courses that Dominique Paret has given in companies, and it provides detailed explanations of the design and operation of the FlexRay bus. Comprised of five parts the book covers: the FlexRay concept and its communication protocol; the FlexRay physical layer; synchronization and global time and; architecture of a node, components and development aid tools for hardware and software.

• Provides comprehensive treatment of the FlexRay network, including its implementation through a real automotive application
• Includes the latest specifications (Version 3) concluded by the FlexRay consortium widely expected to become the industry standard
• Written by an author with in-depth experience of automotive electronics, including FlexRay, and presenter of specialist training courses to the industry
• Includes a review of industrial tools to help design and implement a FlexRay based distributor application

Part B

The FlexRay Concept and its Communication Protocol

For teaching reasons (so that everything is not mixed up!), the purpose of this second part is to present only the most general aspects of the FlexRay concept. Parts C and D of this book will fill in the missing points of the concept in detail. This part therefore presents:

• in Chapter 4, the genesis of FlexRay;
• in Chapter 5, FlexRay and real time;
• in Chapter 6, the communication protocol;
• in Chapter 7, the modes and techniques for access to the medium.

A very specific application example offers a synthesis of the content of the chapters listed above. Also, as you will very quickly appreciate, there are many things that are not said and hidden techniques in one of the parts about modes of access to the medium. Which one? Wait and see! The technical appendix which resolves most of this unbearable suspense forms a whole separate chapter.

Chapter 4

The Genesis of FlexRay

Before presenting the FlexRay concept and its genesis, let us mention, as a reminder, a solution which, for a few years, was claimed to be the solution to the problems mentioned in Chapter 3 for the automotive market. This is the Time Triggered Protocol Class C (TTP/C).

4.1 The TTP/C Protocol

The TTP/C system is one of the members of the large family of ‘time-triggered protocols’ (the ‘/C’ indicates that it meets the criteria of Class C of the Society of Automotive Engineers (SAE) for the real time communication and fault-tolerance aspects of the automotive field). It was designed and developed by Prof. Hermann Kopetz of the University of Technology of Vienna, Austria, and was then taken over by the TTTech company1 (plus some affiliates).

In short, TTP/C was designed on the principle that the strategy for access to the medium would be of the time division multiple access (TDMA) type, to which we will return in detail when we present FlexRay. This principle makes it possible to solve problems of interoperability between CPUs which are developed independently of each other. It should be noted that TTP/C was not originally dedicated to automotive applications, but was aimed at industrial applications generally.

On a certain date in 1997 or 1998, following some presentations which were made to the automotive world, for lack of anything better, some automotive manufacturers such as Audi (and Volkswagen, which is part of the same group) formed a ‘TTA Group’, where the A stood for ‘architecture’. Other manufacturers such as BMW and DaimlerChrysler also worked on the TTP/C design for a few years, but left the group because they judged, for precise technical reasons, that the concept was not aimed sufficiently at the automotive field, and that working with TTTech was quite awkward.

After this interlude, let us now go on to examine FlexRay.

4.2 FlexRay

4.2.1 The Genesis of FlexRay

The genesis of FlexRay began with the formation of a group of industrialists who had decided to carry out an exhaustive technical analysis of existing networks which were used or could be used specifically in the automotive environment—that is, CAN, TTCAN, TCN, TTP/C, Byteflight (a proprietary protocol of BMW)—and to judge whether one of them was capable of meeting, for decades to come, all the technical and application wishes in the preceding chapters. The conclusions of this study clearly indicated that this was not the case, and this led to the definition of a new proposal, which was later called ‘FlexRay’. In fact, in a few words, the inventory of existing solutions showed that:

• CAN
  • does not have a high enough bit rate for the new applications; it is difficult to make transmission really deterministic and redundant;
  • will not be replaced by FlexRay, but will work as a complement to it.
• TTCAN
  • in principle has the same throughput limitations as CAN;
  • regrettably is lacking support for optical transmission, a redundant transmission channel, ‘fault-tolerant Global Time’ and a bus guardian.
• TTP/C
  • has a frame whose information content is judged to be too low;
  • has few common properties with FlexRay, despite the use of bus access of the TDMA type;
  • does not offer or provide any flexibility relative to FlexRay concerning: the combination of the synchronous and asynchronous parts of transmission; the multiple slots for sending by the same node in the synchronous part; nodes acting on single, dual or mixed channels; a ‘never give up’ strategy regarding control of the communication system in relation to the application; the problems of the status of FlexRay members and of rights to licences and services.
• Byteflight
  • has too few functions;
  • can be functionally compatible with FlexRay if the latter is used in pure asynchronous mode.

4.3 The FlexRay Consortium

Following the technical report described above, in 2000, a ‘Consortium Agreement’ was signed between the following industrialists (look out for the first person who says ‘oh hell, always the same people!’):

• the automotive manufacturers BMW AG, DaimlerChrysler AG and General Motors Corporation;
• the equipment manufacturer Robert Bosch GmbH;
• the silicon founders Motorola GmbH (which has since become FreeScale), which is mainly involved in the definition of the protocol and of the communication controller, and Philips GmbH (which has since become NXP Semiconductors), for the definition and the components of the physical layer, but also involved in the definition of the protocol;
• they were joined a little later by the manufacturer Volkswagen AG, to form the core partners of the FlexRay Consortium, each with the mission of bringing its specific skills; on the same occasion, the statuses of premium members and associated members were also defined.

The Guilty

When it's friendly, a little denunciation never hurt anyone! So here is the list of companies and people who worked together in the FlexRay Consortium so that the concept became a reality. As you will notice—and it is rare enough to be emphasised—to show the unwavering desire of the Consortium members to make progress, the (main) patents listed below were filed jointly by all the companies which are core members of the Consortium.

Publication date: 22 October 2003

Patent Numbers and Inventions

• EP1355458 Method for transmitting data within a communication system.
• EP1355461 Method and unit for bit stream decoding.

Applicants

• Bayerische Motoren Werke AG (Germany)
• Robert Bosch GmbH (Germany)
• DaimlerChrysler AG (Germany)
• Gen Motors Corp (US)
• Koninkl Philips Electronics NV (Netherlands)
• Motorola Inc. (US)
• Philips Intellectual Property (Germany).

Inventors

• Ralf Belschner, Josef Berwanger, Florian Bogenberger, Harald Eisele, Bernd Elend, Thomas Fuehrer, Florian Hartwich, ...

Table of contents

• Cover
• Title Page
• Copyright
• Preface
• List of Abbreviations
• Part A: ‘Secure Real Time’ Applications
• Part B: The FlexRay Concept and its Communication Protocol
• Part C: The FlexRay Physical Layer
• Part D: Synchronisation and Global Time
• Part E: Architecture of a Node, Components and Development Aid Tools
• Bibliography
• Index