wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

44
FlexRay
Martin Horauer
University of Applied
Sciences Technikum Wien
Peter Rössler
University of Applied
Sciences Technikum Wien
44.1 Introduction.....................................................................................44-1
44.2 Protocol.............................................................................................44-1
Communication Cycles. •. Framing. •. Startup of a Cluster. •. .
Physical Layer
44.3 System Architecture........................................................................44-4
Topologies. •. Node Architecture. •. Star Couplers
44.4 System Design Considerations......................................................44-5
Configuration. •. AUTOSAR
References....................................................................................................44-7
44.1 Introduction
Today, electronic control units (ECUs), and especially their interoperation, are the driving force behind
most automotive innovations. They allow the establishment of extended and improved functionality
with regard to safety, reliability, environmental efficiency, and comfort (e.g., combining multiple sensor
information to a comprehensive picture of the car’s surrounding). In recent years, more than 50 ECUs
interconnected with different communication subsystems have become common [H05]. This in turn led
to higher demands on communication resulting in a strong increase on the bus traffic. In fact, the communication
subsystem became a bottleneck with regard to bandwidth and reliability.
In 2000, some leading automotive original equipment manufacturers (OEMs) founded an industrial
consortium to develop a new bus protocol termed FlexRay* in order to serve the needs of future automotive
applications. Relying on the time-triggered paradigm, FlexRay addresses reliability and faulttolerance
aspects, namely by implementing a time division multiple access (TDMA) channel access
method and features like bus-guardians or support for redundant physical media. Additional provisions
also support event-triggered communication for an effective coupling of sensor/actuator systems with
lower requirements on reliability.
44.2 Protocol
The FlexRay consortium provides specifications and applications for the electrical physical layer and
a protocol specification [FE05,FP05] as well as conformance test specifications that essentially cover
the physical and data link layer when compared to the ISO/OSI reference model. Network, transport,
session, and presentation layer functionality may be implemented according to the AUTomotive Open
System ARchitecture (AUTOSAR) † standard.
* http://www.flexray.com
†
http://www.autosar.org
44-1
© 2011 by Taylor and Francis Group, LLC