Steer-by-Wire over real-time Ethernet:A TTEthernet based safety-critical Application

CoRE Working Group

Department Informatik, Hamburg University of Applied Sciences

AbstractReal-time (RT) Ethernet is a new, scalable approachto reduce the complexity of in-vehicle networkssignificantly and therefore is a viable candidate forfuture automotive communication. To prove thecapabilities of such a network a real-time Ether-net prototype platform was built, to achieve timingand bandwidth characteristics of typical automo-tive applications. The use-case shows a steer-by-wire application which fulfils the challenging real-time demands of control processes.

Motivation•Using typical hardware for automotive domains

•Achieving timing requirements of in-car com-munication

•Fulfilling demands of real-time capable controlprocesses

ArchitectureSynchronization

•Sub-modules for reception and transmission ofsynchronization frames respectively are provided

•Client functionality provided by receive-moduleonly, whereas masters activate transmission too

•Fault tolerance capable through dynamic down-and upgrading

Scheduler

•Handling time-triggered events, as well as exter-nal events, demands a hybrid design

•Advanced interrupt driven approach through hi-erarchical order of possible tasks

•Preemptive scheduling supports immediate exe-cution of crucial events

Buffer

•Support for multiple buffer types to fulfil differ-ent demands

•Mapping to RT Ethernet buffer structure preventsexpensive memory operations

•Dedicated buffer reduces complexity of algorithmin runtime toO(1)

Fig. 1: Architecture of a TTEthernet platform

Bridge•Tunneling of CAN messages over TT Ethernet

•Connect CAN busses over common network

•Offers VirtualCAN interface for applications

Platform•Based on high integrated system-on-chip

•ARM 9 clocked with 200 MHz

•Four configurable communication channels

•Supports various communication technologies

•Data switching architecture replaces AMBA

•Time base with adjustable resolution of2−28 ns

Network Topology

Steer

CAN-Bus

Bridge

Controller

RT EthernetSwitch 1

CANopen-Bus

Wheel Force sensor

Bridge

RT EthernetSwitch 2

Fig. 2: Network topology of demonstrator

Scheduling

Motor

Force sensor

Bridge Wheel

Zeit µs

100 200 800700300 600500400 900 1000

Real-time Ethernet SYNC Phase

1100 1200 1300 1400 1500

0x252

1600

Controller

Steer

Switch 1

Bridge Steer0x200

0x2100x201

0x211

0x20A

0x21A

1700 1800 1900 2000

Switch 2

0x80 0x1820x183

Fig. 3: Scheduling of time-triggered communication

Controller•Generates CAN messages for communication with

sensors and actors

•Realizes force feedback for driving response

•Sport and cruise mode by demand

• Interface for custom adjustment of parameters

Results• Jitter of schedules<300 ns

•Oscillation behaviour at start-up

•Oscillation ends after runtime<2 s

•Controller delay time 930µs

Fig. 4: Measurement results of jitter and oscilla-tion behaviour at start-up

References[1] K. Muller, T. Steinbach, F. Korf, and T. C. Schmidt, “A Real-time

Ethernet Prototype Platform for Automotive Applications,” in Pro-ceedings of the 1st IEEE International Conference on ConsumerElectronics - Berlin (ICCE-Berlin), 2011, to appear.

[2] J. Kamieth, “Entwurf einer Mikrocontroller basierten Bridge zurKopplung von CAN Bussen ber Time-Triggered Realtime Ethernet,”Aug. 2011, Bachelorthesis.

[3] K. Muller, “Time-Triggered Ethernet fur eingebettete Systeme:Design, Umsetzung und Validierung einer echtzeitfahigenNetzwerkstack-Architektur,” Aug. 2011, Bachelorthesis.

[4] V. Stepanov, “Mikrocontroller und CAN-basierte verteilteRegelungeiner Steer-by-Wire Lenkung mit harten Echtzeitanforderungen,”Aug. 2011, Bachelorthesis.

Contact information: Franz Korf, Thomas C. Schmidt, Till Steinbach, Florian Bartols, Kai Muller, Vitalij Stepanov, Friedrich Groß: HAW Hamburg, Dept. Informatik, Berliner Tor 7, D-20099 Hamburg

Email: {korf, schmidt,till.steinbach, florian.bartols, kai.mueller, vitalij.stepanov, friedrich.gross}@informatik.haw-hamburg.de