Wilamowski B.M., Irwin J.D. The Industrial Electronics Handbook. Second Edition: Industrial Communication Systems

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Protocols of the Time-Triggered Architecture: TTP, TTEthernet, TTP/A 43-7

43.5.4 Fault-tolerant ttEthernet Conguration

In.the.safety-critical. conguration.of. TTEthernet,.the. network.provides.its.services.in.the.pres-

ence

.of.node.or.communication.channel.failures.[AKG+06]..To.tolerate.a.fault.in.a.communication.

channel,.a.safety-critical TTEthernet controller,.which.transmits.and.receives.redundant.messages.

using.two.distinct.communication.channels,.is.required..A.message.that.should.be.redundantly.sent.

on.two.communication.channels.is.called.protected TT message..In.a.safety-critical.conguration,.

a.TTEthernet.switch.is.accompanied.by.a.guardian.controlling.the.input.and.output.ports.of.the.

switch.. e.guardian.has.knowledge.about.the.time-triggered.schedule.of.all.protected TT messages.

and.dynamically.disables.all.input.ports.that.could.possibly.interfere.with.the.transmission. of.a.

protected.TT.message.

43.5.5 Clock Synchronization

The.clock.synchronization.mechanisms.in.TTEthernet.can.be.adapted.to.the.specific.requirements.

of.the.actual.applications..The.initial.establishment.of.the.global.time.after.start-up.and.the.main-

tenance

.of.this.time.during.operation.is.performed.by.a.subset.of.TTEthernet.controllers.called.

time-keeping controllers.[KAGS05]..The.most.basic. form.that. is.supported.is.the.central master

algorithm.

.In.this.case,.a.single.time-keeping.controller—the.master—will.periodically.send.out.a.

resynchronization.message.containing.its.local.time..Being.aware.of.the.transmission.latency.of.the.

clock.synchronization.message,.the.individual.nodes.can.adjust.their.clock.according.to.the.time.

value.in.the.synchronization.message.

.tolerate.a.fail-stop failure.of.the.time-master,.a.shadow.master.can.be.employed.that.takes.over.

when.the.current.master.stops.sending.synchronization.messages.

.the.most.dependable.conguration,.multiple.time-keeping.controllers.can.execute.a.Byzantine

resilient

.clock.synchronization.algorithm.that.is.able.to.tolerate.an.arbitrary.failure.of.any.controller.

43.6 ttP/a

 e.time-triggered.eldbus.TTP/A.is.intended.for.the.integration.of.smart.transducers.in.all.types.of.

distributed.real-time.control.systems..Although.the.rst.targets.are.automotive.applications,.TTP/A.

has.been.designed.to.meet.the.requirements.of.process.control.systems.as.well..TTP/A.provides.a.well-

dened

.smart.transducer.interface.to.the.sensors.and.actuators.of.a.network..TTP/A.is.a.master/slave.

Global time counter

Oset bits

15 14 13 12 11 10 9

Period 15

Period 14

Period 13

Period 12

Period 11

Period 10

Period 9

Period 8

Period 7

Period 6

Period 5

Period 4

Period 3

Period 2

Period 1

Period 0

8 7 6 5 4 3 2 1 0

–1

–2

–3

–4

–5

–6

–7

–8

–9

–10

–11

–12

–13

–14

–15

–16

–17

–18

–19

–20

–21

–22

–23

–24

–25

–26

32 s

61 s

8 s

4 s

2 s

1 s

500 ms

250 ms

125 ms

62.5 ms

31.2 ms

15.6 ms

7.8 ms

3.9 ms

1.95 ms

976.5 μs

488.2 μs

244.1 μs

122 μs

61 μs

30.5 μs

15.2 μs

7.6 μs

3.8 μs

1.9 μs

953.6 ns

476.8 ns

238.4 ns

119.2 ns

59.6 ns

29.8 ns

14.9 ns

FIGURE 43.6 Period.and.phase.(oset).

43-8 Industrial Communication Systems

protocol.that.has.no.fault-tolerance.mechanisms.by.default,.but.supports.deterministic.real-time.com-

munication

.wit

.low.lat

ency

.and.sma

.jit

ter.

.TTP

.sup

ports

.low

-cost

.imp

lementations

.on.a.wid

.set.of.

ava

ilable

.co

mponent-o-the-shelf

.mi

crocontrollers.

TTP/A

.has.bee

.sta

ndardized

.in.200

.by.the.Obje

.Man

agement

.Gro

.(OM

.as.sma

rt transducer

interface

.sta

ndard

.[OM

G03].

. e.sta

ndard

.com

prises

.TTP

.as.the.tim

e-triggered

.tra

nsport

.ser

vice

wit

hin

.a.dis

tributed

.sma

.tra

nsducer

.sub

system

.and.de

nes

.a.wel

l-dened

.int

erface

.bet

ween

.the.tra

ns-

ducers

.an

.a.CO

RBA

.ne

twork.

.sma

rt-sensor

.tec

hnology

.oe

.a.numb

.of.adv

antages

.fro

.the.poi

nts

.of.vie

.of.tec

hnology,

cos

.an

.co

mplexity

.ma

nagement

.[K

op00]:

•

. Electrically.weak.nonlinear.sensor.signals.can.be.conditioned,.calibrated,.and.transformed.into.

dig

ital

.for

.on.a.sing

.sili

con

.die.wit

hout

.any.noi

.pic

kup

.fro

.lon

.ext

ernal

.sign

.tra

nsmis-

sion

.li

nes

.[D

W98].

•

. e.sma

.sen

sor

.con

tains

.a.wel

l-specied

.dig

ital

.com

munication

.int

erface

.to.a.sen

sor

.bus

.oe

ing

.“pl

ug-and-play”

.cap

ability

.if.the.sen

sor

.con

tains

.a.ref

erence

.to.its.doc

umentation

.in.for

.of.

an.el

ectronic

.da

.sh

eet

.as.it.is.pr

oposed

.in.th

.IE

.14

51.2

.Sta

ndard

.[E

cc98].

•

. It.is.pos

sible

.to.mon

itor

.the.loc

.ope

ration

.of.the.sen

sing

.ele

ment

.via.the.net

work

.and.thu

.sim-

lify

.th

.di

agnosis

.at.th

.sy

stem

.le

vel.

.int

ernal

.com

plexity

.of.the.sma

rt-sensor

.har

dware

.and.so

ware

.and.int

ernal

.fai

lure

.mod

.can.

be.hidden.from.the.user.by.well-designed.fully.specied.smart-sensor.interfaces.that.provide.just.those.

ser

vices

.th

.us

.is.in

terested

.in

43.6.1 Interface File System

 e.information.transfer.between.a.smart.transducer.and.its.client.is.achieved.by.sharing.informa-

tion

.tha

.is.con

tained

.in.an.int

ernal

.int

erface

.le.sys

tem

.(IF

S),

.whi

.is.enc

apsulated

.in.eac

.sma

tra

nsducer.

.IFS.pro

vides

.a.uni

que

.add

ress

.sch

eme

.for.tra

nsducer

.dat

.con

guration

.dat

.sel

f-describing

inf

ormation,

.and.int

ernal

.sta

.rep

orts

.of.a.sma

.tra

nsducer

.[KH

E01].

.It.est

ablishes

.a.sta

ble

.int

ermedi-

ate

.str

ucture

.tha

.is.a.sol

.bas

.for.sma

.tra

nsducer

.ser

vices.

. e.imp

lementation

.of.the.IFS.is.eco

nomically

.fea

sible

.to.assi

.loc

.int

elligence

.eve

.to.low

-cost

.I/O.dev

ices

.lik

.8.bit.mic

rocontrollers

wit

.4.kb

ytes

.Fl

ash

.RO

.an

.le

.th

.64.by

tes

.of.RA

.me

mory.

The

.IFS.is.the.sou

rce

.and.sin

.for.all.com

munication

.act

ivities

.and.act

.as.a.tem

poral

.fir

ewall

[KN

97]

.tha

.dec

ouples

.the.loc

.tra

nsducer

.app

lication

.fro

.the.com

munication

.act

ivities.

.A.tim

triggered

.sen

sor

.bus.wil

.per

form

.a.per

iodical

.tim

e-triggered

.com

munication

.to.cop

.dat

.fro

the.IFS.to.the.fie

ldbus

.and.wri

.rec

eived

.dat

.int

.the.IFS

.The.ROD

L—a

.pre

defined

.com

mu-

nication

. sch

edule—defines

. tim

. ori

gin,

.and. des

tination

. of. eac

. pro

tocol

.com

munication.

. The.

ins

tants

.of.upd

ates

.are.spe

cified

.a.pri

ori

.and.kno

.by.the.com

municating

.nod

es.

.Thu

.the.IFS.

act

.as.a. tem

porally specified interface

.tha

.dec

ouples

.the.loc

.tra

nsducer

.app

lication

.fro

.the.

com

munication

.tas

Each

.tra

nsducer

.can.con

tain

.up.to.64.le

.in.its.IFS

.An.IFS.le.is.an.ind

exed

.seq

uential

.arr

.of.up.

to.256.rec

ords.

.A.rec

ord

.has.a.xe

.len

gth

.of.4.byt

.(32.bit

s).

.An.IFS.rec

ord

.is.the.sma

llest

.add

ressable

uni

.wit

hin

.a.sma

.tra

nsducer

.sys

tem.

.Eve

.rec

ord

.of.an.IFS.le.has.a.uni

que

.hie

rarchical

.add

ress

(which.also.serves.as.the.global.name.of.the.record).consisting.of.the.concatenation.of.the.cluster.name,.

the.lo

gical

.no

.na

me,

.th

.l

.na

me,

.an

.th

.re

cord

.na

me.

.loc

.app

lications

.in.the.sma

.tra

nsducer

.nod

.are.abl

.to.exe

cute

.a.clu

sterwide

.app

lication

.by.

com

municating

.dir

ectly

.wit

.eac

.oth

er.

.Fig

ure

.43.

.dep

icts

.the.log

ical

.net

work

.vie

.for.suc

.a.clu

ster-

wide

.ap

plication.

Protocols of the Time-Triggered Architecture: TTP, TTEthernet, TTP/A 43-9

43.6.2 the three Interfaces of a Smart transducer

In.order.to.support.complexity.management.and.composability,.it.is.useful.to.specify.distinct.interfaces.

for.functionally.dierent.services.[Kop00]..As.depicted.in.Figure.43.8,.a.smart.transducer.node.can.be.

accessed.via.three.dierent.interfaces.

Real-Time Service Interface

.real-time.service.(RS).interface.provides.the.timely.real-time.services.to.the.component.during.the.

operation.of.the.system.

Diagnostic and Maintenance Interface

.diagnostic.and.maintenance.(DM).interface.opens.a.communication.channel.to.the.internals.of.a.

component..It.is.used.to.set.parameters.and.to.retrieve.information.about.the.internals.of.a.component,.

for.example,.for.the.purpose.of.fault.diagnosis.. e.DM.interface.is.available.during.system.operation.

without.disturbing.the.real-time.service..Usually,.the.DM.interface.is.not.time-critical.

Actuator

Local sensor

application

Local sensor

application

e.g., control

Sensor

Distributed interface file system

Local sensor

application

Distributed

application

FIGURE 43.7 Logical.network.structure.

Local sensor

application

Sensor or

actuator

Interface le

system

Real-time service

interface

Conguration and

planning interface

Diagnostics and

management interface

Smart transducer

Read/write access

FIGURE 43.8 ree.interfaces.to.a.smart.transducer.node.

43-10 Industrial Communication Systems

Conguration and Planning Interface

During

.the.integration.phase,.the.conguration.and.planning.(CP).interface.is.used.to.generate.the.

“glue”.between.the.nearly.autonomous.components,.that.is,.the.time-triggered.schedule.and.communi-

cation

.endpoints.. e.CP.interface.is.not.time-critical.

43.6.3 Principles of Operation

TTP/A.is.a.TTP.supporting.two.types.of.communication:.(1).master–slave.communication.between.

an.active.master.and.a.selected.transducer.node.and.(2).multipartner.communication.among.several.

smart.transducer.nodes.. e.master.is.required.for.both.communication.modes.in.order.to.establish.a.

common.time.base.among.the.nodes..In.case.of.a.crash.failure.of.the.master,.a.shadow.master.can.take.

control..Every.node.in.this.cluster.has.a.unique.alias,.an.8.bit.(1.byte).integer,.which.can.be.assigned.to.

the.node.a.priori.or.set.via.the.conguration.interface.

.bus.allocation.is.done.by.a.TDMA.scheme..Communication.is.organized.into.rounds.consisting.

of.several.TDMA.slots..A.slot.is.the.unit.for.transmission.of.one.byte.of.data..Data.bytes.are.transmit-

ted

.in.a.standard.UART.format..Each.communication.round.is.started.by.the.master.with.a.so-called.

reworks.byte.. e.reworks.byte.denes.the.type.(e.g.,.multipartner.or.master–slave).of.the.round.and.

is.a.reference.signal.for.clock.synchronization..Followed.by.the.reworks.byte.are.a.number.of.data.

bytes.. e.communication.pattern.for.each.round.is.predened.via.the.RODL,.which.is.distributively.

stored.in.all.nodes.

 ere

.are.eight.dierent.rework.bytes.encoded.by.a.redundant.bit.code.supporting.error.detection..

One.reworks.byte.is.a.regular.bit.pattern,.which.is.also.used.by.slave.nodes.with.an.imprecise.on-chip.

oscillator.for.startup.synchronization.(see.Figure.43.9)..Between.2.data.bytes,.there.is.an.extra.Inter-Byte.

Gap.(IBG).in.order.to.account.for.a.switching.time.between.dierent.senders.. e.IRG.denes.a.time.of.

silence.between.two.consecutive.rounds.

0 1 2 3 4 5 6 7

Odd

Synchronize pattern

IRG

UART−Frame 11−bit

IBG

Start

LSB

MSB

Stop

Partity

TTP/A Slot−13 bit

FIGURE 43.9 Synchronization.pattern.

Slot 0 Slot nSlot 1 Slot 2

(Master)

FB.................. Fireworks Byte, sent by master

DataByte...... sent either by master or slave

DataByte

Slot 0

Multipartner round

Last slot of round

DataByte DataByte

(Master)

FIGURE 43.10 Example.for.a.TTP/A.multipartner.round.

Protocols of the Time-Triggered Architecture: TTP, TTEthernet, TTP/A 43-11

Generally,.there.are.two.types.of.rounds:

Multipartner round

.round.consists.of.a.conguration.dependent.number.of.slots.and.an.assigned.sender.node.for.each.

slot.. e.conguration.of.a.round.is.dened.in.a.data.structure.called.“RODL”.(ROund.Descriptor.List)..

 e.RODL.denes.which.node.transmits.in.a.certain.slot,.the.operation.in.each.individual.slot,.and.the.

receiving.nodes.of.a.slot..RODLs.must.be.congured.in.the.slave.nodes.prior.to.the.execution.of.the.

corresponding.multipartner.round..An.example.for.a.multipartner.round.is.depicted.in.Figure.43.10.

Master/slave round

.master/slave.round.is.a.special.round.with.a.xed.layout.that.establishes.a.connection.between.the.

master.and.a.particular.slave.for.accessing.data.of.the.node’s.IFS,.for.example,.the.RODL.information..

In.a.master/slave.round,.the.master.addresses.a.data.record.using.a.hierarchical.IFS.address.and.species.

an.action.like.reading.of,.writing.on,.or.executing.that.record.

.master/slave.rounds.are.used.to.access.the.DM.and.the.CP.interface.to.the.transducer.nodes..

Communication.via.the.RS.interface.is.established.by.periodical. multipartner.rounds..Master/slave.

rounds.are.scheduled.periodically.between.multipartner.rounds.as.depicted.in.Figure.43.11.in.order.to.

enable.maintenance.and.monitoring.activities.during.system.operation.without.a.probe.eect.

acknowledgments

 is.survey.was.supported.by.the.Austrian.FWF.project.TTCAR.under.contract.No..P18060-N04.

references

[AFI+00].Alcatel.Corp.,.Fujitsu.Ltd.,.IBM,.NEC.Corp.,.NTT.Corp.,.and.IONA.Tech..Management.of.

event.domains..OMG.TC.Document.telecom/2000-01-01,.January.2000..Available.at.http://www.

omg.org.

[AKG+06]

.A..Ademaj,.H..Kopetz,.P..Grillinger,.K..Steinhammer,.and.A..Hanzlik..Fault-tolerant.time-

triggered

.ethernet.conguration.with.star.topology..In.Dependability and Fault Tolerance Workshop,.

Frankfurt,.Germany,.March.2006.

[BP00]

.G..Bauer.and.M..Paulitsch..An.investigation.of.membership.and.clique.avoidance.in.ttp/c..In.the

IEEE Symposium on Reliable Distributed Systems,

.Nürnberg,.Germany,.October.16–18,.2000.

[DeL99]

.R..DeLine..Resolving.packaging.mismatch,.PhD.thesis,.Computer.Science.Department,.Carnegie.

Mellon.University,.Pittsburgh,.PA,.June.1999.

[DW98]

.P..Dierauer.and.B..Woolever..Understanding.smart.devices..Industrial Computing,.47–50,.October.

1998.

[Ecc98]

.L..H..Eccles..A.brief.description.of.IEEE.P1451.2..In.Sensors Expo,.San.Jose,.CA,.May.1998.

[EHK01]

.W..Elmenreich,.W..Haidinger,.and.H..Kopetz..Interface.design.for.smart.transducers..In.IEEE

Instrumentation and Measurement Technology Conference,

.Budapest,.Hungary,.May.2001,.Vol..3,.

pp..1642–1647.

MP round

MP roundMS round

MS round

Cluster cycle time

Real-time

service data

Diagnostics and

management data

FIGURE 43.11 Recommended.TTP/A.schedule.

43-12 Industrial Communication Systems

[Fle05].Flexray.Consortium..FlexRay.Communications.System.Protocol.Specication.Version.2.1,.2005..

Avai

lable

.at.ht

tp://www.exray.com.

[HMFH00]

.F..Har

twich,

.B..Mül

ler,

.T..Führ

er,

.and.R..Huge

.Time.trig

gered

.communic

ation

.on.CAN..In.

Pro

ceedings Seventh International CAN Conference,

.Am

sterdam,

.th

.Net

herlands,

.2000.

[KA

GS05]

.H..Kop

etz,

.A..Adema

.P..Gri

llinger,

.and.K..Stein

hammer.

. e.time-t

riggered

.ether

net

.(tte).

design..In.e IEEE

International Symposium on Object-oriented Real-time distributed Computing

(ISORC),

.Se

attle,

.WA,.Ma

.2005.

[KB03]

.H..Kop

etz

.and.G..Bauer

. e.time-t

riggered

.arc

hitecture.

.Pro

ceedings of the IEEE,

.91(1):.112–126,.

Jan

uary

.2003.

[KHE01]

.H..Kop

etz,

.M..Holzm

ann,

.and.W..Elmenr

eich.

.A.univer

sal

.smar

.tran

sducer

.inter

face:

.TTP/A..

Int

ernational Journal of Computer System Science & Engineering,

.16(2):.71–77,.Ma

rch

.2001.

[KN97]

.H..Kop

etz

.and.R..Noss

al.

.Temp

oral

.rewa

lls

.in.lar

.dist

ributed

.rea

l-time

.system

.Pro

ceedings

of the Sixth IEEE Workshop on Future Trends of Distributed Computing Systems (FTDCS’97),

.Tunis,.

Tunisi

.1997,.pp

.310–315.

[KO87]

.H..Kop

etz

.and.W..Och

senreiter.

.Cloc

.sync

hronization

.in.dist

ributed

.rea

l-time

.system

.IEEE

Tra

nsactions on Computers,

.C-36(8):.933–940,.1987.

[Ko

p92]

.H..Kop

etz.

.Spa

rse

.time.vers

.dense.time.in.dist

ributed

.rea

l-time

.system

.In.Pro

ceedings of the

12th International Conference on Distributed Computing Systems,

.Yo

kohama,

.Ja

pan,

.Jun

.1992.

[Ko

p00]

.H..Kop

etz.

.So

ware

.engin

eering

.for.rea

l-time:

.A.roadm

ap.

.In.Pro

ceedings of the IEEE Soware

Engineering Conference,

.Limmerick,.Ireland,.2000.

[OM

G02]

.OMG..Sma

.Tran

sducers

.Int

erface.

.Spe

cication

.ptc/2002-05-01,.Obj

ect

.Man

agement

.Gro

up,

May.2002..Ava

ilable

.at.ht

tp://www.omg.org/.

[OMG03]

. Obj

ect

. Man

agement

. Gro

. (OMG).. Sma

. Tran

sducers

. Int

erface

. V1.0,. Jan

uary

. 2003..

Spe

cication

.ava

ilable

.at.ht

tp://doc.omg.org/formal/2003-01-01

.as.doc

ument

.pt

c/2002-10-02.

[SAE95a]

.Cla

.A.app

lication/denition

.(sae.j2057/1.jun91)..In.SAE Ha

ndbook,

.Vol

.2,.pp..23.478–23.484..

Societ

.of.Aut

omotive

.Engin

eers,

.Inc.,.War

rendale,

.PA,.1995..Repo

.of.the.SAE.Vehic

.Netw

ork

for.Mu

ltiplex

.an

.Da

.Co

mmunication

.St

andards

.Co

mmittee

.ap

proved

.Jun

.1991.

[SAE95b]

.SAE..Cla

.C.app

lication

.req

uirements,

.surv

.of.kno

.pro

tocols,

.J20056..In.SAE Ha

ndbook,

pp..23.437–23.461..SAE.Pr

ess,

.Wa

rrendale,

.PA,.1995.

[SGAK06]

.Kla

.Stein

hammer,

.Petr.Gri

llinger,

.Ast

rit

.Adema

.and.Herm

ann

.Kop

etz.

.A.time-t

riggered

ether

net

.(tte).swit

ch.

.Des

ign, Automation and Test in Europe,

.Munich,.Germ

any,

.Mar

.6–10,.2006.

[TT

A03]

.TTA

Group.

.Spec

ication

.of.the.TTP

.Pro

tocol

.V1.

.200

.Ava

ilable

.at.htt

p://www.ttagroup.org.

44-1

44.1 Introduction

Today,.electronic.control.units.(ECUs),.and.especially.their.interoperation,.are.the.driving.force.behind.

most.autom

otive

.inno

vations.

. ey.allo

.the.esta

blishment

.of.exte

nded

.and.impr

oved

.func

tionality

with.rega

.to.safe

ty,

.reli

ability,

.envi

ronmental

.eci

ency,

.and.comf

ort

.(e.g

.combi

ning

.mult

iple

.sens

info

rmation

.to.a.comp

rehensive

.pict

ure

.of.the.car’

.surr

ounding).

.In.rece

.year

.more.than.50.ECUs.

inte

rconnected

.with.die

rent

.comm

unication

.subs

ystems

.have.beco

.comm

.[H05

. is.in.turn.led.

to.high

.dema

nds

.on.comm

unication

.resu

lting

.in.a.stro

.incr

ease

.on.the.bus.tra

.In.fact

.the.com-

unication

.sub

system

.bec

ame

.a.bot

tleneck

.wit

.reg

ard

.to.ban

dwidth

.and.rel

iability.

.2000

.some.lead

ing

.autom

otive

.orig

inal

.equi

pment

.manu

facturers

.(OEM

.foun

ded

.an.indu

strial

cons

ortium

.to.deve

lop

.a.new.bus.proto

col

.term

.Flex

Ray*

.in.orde

.to.serv

.the.need

.of.futu

.auto-

otive

.appl

ications.

.Rely

ing

.on.the.time

-triggered

.para

digm,

.Flex

Ray

.addr

esses

.reli

ability

.and.faul

tolerance

.aspe

cts,

.name

.by.impl

ementing

.a.time.divi

sion

.mult

iple

.acce

.(TDM

.chan

nel

.acce

meth

.and.feat

ures

.like.bus-

guardians

.or.supp

ort

.for.redu

ndant

.physi

cal

.medi

.Addi

tional

.prov

isions

also.supp

ort

.even

t-triggered

.comm

unication

.for.an.eec

tive

.coup

ling

.of.sens

or/actuator

.syst

ems

.with.

lowe

.req

uirements

.on.rel

iability.

44.2 Protocol

 e.FlexRay.consortium.provides.specications.and.applications.for.the.electrical.physical.layer.and.

a.proto

col

.spec

ication

.[FE0

5,FP05]

.as.well.as.conf

ormance

.test.spec

ications

.that.esse

ntially

.cove

the.physi

cal

.and.data.link.laye

.when.comp

ared

.to.the.ISO/

OSI

.refe

rence

.mode

.Netw

ork,

.tran

sport,

sessi

on,

.and.pres

entation

.laye

.func

tionality

.may.be.impl

emented

.acco

rding

.to.the.AUTo

motive

.Open.

Syst

.ARc

hitecture

.(AU

TOSAR)

†

.standard.

http://www.exray.com

†.

http://www.autosar.org

FlexRay

44.1. Introduction.....................................................................................44-1

44.2

. Proto

col.............................................................................................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

Conguration. •. AUTOSAR

References.....................................................................................................44-7

Martin Horauer

University of Applied

Scie

nces

Tec

hnikum

Wie

Peter Rössler

University of Applied

Scie

nces

Tec

hnikum

Wie

44-2 Industrial Communication Systems

44.2.1 Communication Cycles

 e.communication.in.FlexRay.is.arranged.in.periodic.cycles.where.every.cycle.consists.of.a.static.seg-

ment,

.an.optional.dynamic.segment,.a.symbol.window,.and.a.network.idle.time.phase,.cf..Figure.44.1..

Communication.cycles.are.numbered.sequentially.from.0.to.cycle.63;.aer.cycle.63,.the.cycle.count.starts.

anew.at.0..Every.node.transmits.data.in.the.static.or.the.(optional).dynamic.segment..While.the.static.

segment.provides.a.communication.mechanism.for.reliable.data.transmissions,.the.dynamic.segment.

is.intended.to.be.used.for.nonsafety.critical.sporadic.messages.. e.symbol.window.is.used.to.transmit.

media.test.symbols.in.order.to.check.the.integrity.of.the.optional.bus-guardians,.cf..Section.44.3.. e.

network.idle.time.is.used.for.the.oset.correction.of.the.local.clock.of.every.node.. erefore,.FlexRay.

uses.a.distributed.clock.synchronization.scheme.by.employing.a.fault-tolerant.midpoint.algorithm;.see.

[WL88].for.further.details..Selected.nodes.send.synchronization.messages.(having.the.sync.bit.set,.see.

below);.these.messages.get.timestamped.at.every.receiver.and.form.the.input.for.the.clock.synchroniza-

tion

.algorithm.along.with.the.node’s.local.clock.

.the. static. segment,.communication. follows. a. TDMA. scheme..Herein,. frames.are. transmitted.

within.one.or.multiple.preassigned.time.slots.all.having.an.equal.length..In.particular,.transmission.

within.an.assigned.slot.starts.aer.the.so-called.action-point.oset.(see.Figure.44.1).and.ceases.some.

time.before.the.end.of.the.slot.is.reached.. ese.times.as.well.as.the.assignment.of.slots.to.nodes.is.

congured.at.design.time,.that.is,.before.a.FlexRay.cluster.is.put.into.operation.. e.number.of.slots.n.

within.the.static.segment.can.be.congured.between.2.and.1023.

Using

.a.minislotting.access.scheme,.the.dynamic.segment.is.divided.into.multiple.slots.of.equal.length.

numbered.in.increasing.sequence..A.node.may.send.a.message.whenever.its.congured.frame.identier.

matches.the.slot.number..In.this.case,.the.actual.slot.gets.elongated.by.a.multiple.number.of.minislots.

up.to.the.end.of.the.dynamic.segment..However,.when.no.message.is.transmitted,.a.slot.takes.up.only.

the.length.of.one.minislot..In.both.situations,.the.slot.counter.is.incremented.aer.one.slot..Nodes.may.

not.be.able.to.send.frames.with.higher.identiers.in.the.dynamic.segment.when.other.frames.with.lower.

identiers.have.been.sent.before.

Static segment

Header segment

Payload segment

Trailer segment

Dynamic segment

Communication cycle (CC

)

Static slot

Action point offset

Static slot

Minislot

m–1

Minislot

Symbol

window

Network

idle time

FIGURE 44.1 Communication.cycle.

FlexRay 44-3

44.2.2 Framing

A.frame.sent.in.either.the.static.or.dynamic.segment.consists.of.a.header,.the.payload,.and.a.trailer..

 e.5-byte.long.header.is.made.up.of.ve.control.bits,.an.11.bit.long.frame.identier,.a.payload.length.

eld,.a.header.cyclic.redundancy.checksum.(CRC),.and.a.cycle.count.eld;.cf..Figure.44.2.. e.header.

CRC.secures.the.sync frame indicator.bit,.the.startup frame indicator.control.bit,.the.frame.identier,.

and.the.payload length.eld.. e.payload.holds.an.even.number.of.bytes.(between.0.and.254).that.carry.

the.application.data..When.the.payload.preamble.indicator.control.bit.in.the.header.is.set,.a.part.of.

the.payload.in.the.static.segment.is.reserved.for.network.management.information..Special.cases.are.

nullframes.that.are.identied.by.the.nullframe indicator.control.bit.set.in.the.header;.these.frames.have.

all.the.payload.bits.set.to.zero..Null.frames.are.sent.autonomously.by.the.network.controller.whenever.

no.new.data.are.at.hand.from.the.node’s.host.. e.trailer.contains.a.CRC.over.the.entire.frame.with.a.

Hamming.distance.of.6.for.frame.lengths.up.to.248.bytes.payload.and.a.Hamming.distance.of.4.for.

frame.lengths.between.249.and.254.bytes.payload..With.a.Hamming.distance.of.6,.up.to.5.arbitrary.bit.

ips.can.be.detected.

44.2.3 Startup of a Cluster

When.the.cluster.is.not.running.(e.g.,.aer.power-up).the.host.of.a.dedicated,.so-called.coldstart.node.

may.try.to.start.the.cluster..It.sends.a.collision avoidance symbol.and.waits.for.a.response.within.a.con-

gured

.time..When.no.response.is.received,.the.node.stops.its.start-up.attempts.and.waits.for.an.attempt.

from.another.node.to.start.the.cluster..When.the.latter.occurs,.the.leading.coldstart.node.will.reply.and.

synchronize.its.timebase..Both.nodes.will.now.make.the.transition.to.an.active.state.and.other.noncold-

start

.nodes.may.join.the.cluster,.see.[FE05].or.[R08].for.details.

44.2.4 Physical Layer

FlexRay.employs.a.variant.of.the.inverted.non-return-to-zero.(NRZ-I).coding.for.bit.transmission..

Astandard.NRZ-I.code.represents.a.“One”.with.a.change.in.the.physical.level.whereas.a.“Zero”.is.with.

no.change.. e.modication.of.the.employed.coding.consists.of.a.byte-start sequence.(the.bit.combi-

nation

.“10”).that.is.prepended.to.every.byte.. e.falling.edge.between.these.two.bits.is.used.for.bit-

resynchronization.

.Furthermore,.every.frame.transmission.is.prepended.by.a.transmission start.and.a.

frame start sequence.. e.transmission.start.sequence.consists.of.3–15.bits.and.is.used.to.activate.star.

couplers..Since.activation.takes.some.time,.a.few.bits.of.the.transmission.start.sequence.are.usually.

consumed.by.them..Furthermore,.the.end.of.a.frame.is.followed.by.a.frame end sequence.consisting.of.

the.bits.“01,”.and.an.idle.phase.where.the.transmitter.is.turned.o..Figure.44.3.illustrates.the.coding.of.

an.entire.FlexRay.frame..

Payload segment

(0 ... 254 bytes)

Trailer segment

(3 bytes)

Frame identiﬁer

Startup frame indicator

Sync frame indicator

Nullframe indicator

Payload preamble indicator

Reserved bit

Payload length

Header CRC

Cycle count Payload Frame CRC

Header segment (5 bytes)

FIGURE 44.2 Frame.format.

44-4 Industrial Communication Systems

In.the.dynamic.segment,.an.additional.dynamic trailing sequence.is.inserted.aer.the.frame.end.

sequence.. e.dynamic.trailing.sequence.is.a.low.period.of.variable.length.followed.by.a.high.bit;.it.

extends.a.frame.until.the.next.action.point.

Termination

.needs.to.be.applied.at.the.two.nodes.that.are.set.apart.with.the.longest.wiring.distance..

It.is.calculated.as.equal.to.the.nominal.cable.impedance.between.the.two.points..One.concept.is.split.

termination,.where.one.half.of.the.cable.impedance.to.ground.is.connected.between.the.two.bus.lines..

Furthermore,.a.common.mode.choke.should.be.applied.between.bus.driver.and.termination.circuitry.

.maximum.transfer.rate.is.10.Mbps/channel.allowing.for.a.maximum.cable.length.of.up.to.24.m.

between.two.active.components..Hence,.when.two.cascaded.star.couplers.are.in.use.up.to.72.m.can.be.

spanned.at.10.Mbps..Lowering.the.data.transfer.rates.allows.elongating.the.cabling;.in.particular,.reduc-

ing

.the.data.rate,.for.example,.to.5.Mbps,.allows.doubling.the.cabling.distance.

.standard.species.an.electrical.physical.layer.using.either.shielded.or.unshielded.twisted.pair.

cables..An.optical.medium.can.be.used.as.well;.however,.the.latter.is.not.yet.specied.in.the.standard.

44.3 System architecture

To.address.the.diverse.requirements.of.the.automotive.industry,.the.FlexRay.specication.allows.for.

alot.of.dierent.topologies.and.options.in.the.node.design.

44.3.1 topologies

A.communication.system.of.multiple.nodes.connected.via.at.least.one.communication.channel.directly.(bus.

topology).or.by.star.couplers.(star.topology).is.called.a.cluster..FlexRay.supports.point-to-point,.linear.bus,.

star.topologies,.or.hybrids.thereof.cascaded.with.up.to.two.star.couplers,.cf..Figure.44.4..Furthermore,.com-

munication

.can.take.place.in.a.redundant.fashion.via.two.separate.channels.or.in.a.nonredundant.fashion.

.maximum.of.22.active.nodes.may.be.attached.to.one.segment.(a.linear.bus.or.a.passive.star);.there.

is,.however,.no.guarantee.that.such.a.system.is.operational..It.is.up.to.the.system.designer.to.verify.the.

electrical.interplay.between.bus.drivers,.cables,.and.termination.circuitry.

# Bits:

Idle

Transmission

start sequence

Frame start

sequence

Byte start

sequence

Frame end

sequence

1 2 8 82 2

15...

FIGURE 44.3 Coded.frame.(static.segment).

Node A Node B Node C

Star coupler Star coupler

Node D Node E Node A Node B Node C Node D

FIGURE 44.4 Topology.examples.