FlexRay and Automotive Networking FlexRay and Automotive Networking FutureFuture

Chris QuigleyChris Quigley

Warwick Control TechnologiesWarwick Control Technologies

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Presentation OverviewPresentation Overview

High Speed and High Integrity NetworkingWhy FlexRay? CAN ProblemsTime Triggered Network PrinciplesTime Triggered Protocol CandidatesFlexRay protocol and Applications: BMW, Audi, SAPECS

Other Emerging Protocols and StandardsSummary

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Why FlexRay?Why FlexRay?CAN is extremely cost effective and powerful technology

However, for more intensive applications, it is reaching its limit

CAN ProblemsUnpredictable Latency (unless you buy into expensive solutions)

Undetected bit errors (1.3 x 10-7)

Bandwidth Limitation – 500Kbit/s typical maximum (1Mbit/s possible)

Too expensive for intelligent sensors and actuators

Emerging X-by-Wire and high integrity applications

Complicated automotive architectures• More design effort

• Weight increase from additional ECUs, gateways, connectors

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Why FlexRay? Why FlexRay? –– CAN LatencyCAN Latency

Typical CAN bus characteristic –unpredictable latency

Typical TT network characteristic –predictable latency

Bus Load

Message Latency

Message Latency

Bus Load

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Why FlexRay? Why FlexRay? –– Complicated ArchitecturesComplicated Architectures

CAN de-facto standard but problems include:

Wiring running the length of the vehicle

Too many ECUs – design complexity

Not robust enough for future X-by-wire

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Emerging Networks - Nodal Costing

TTP/CMOST25(Optical)

FlexRay II

Relative Cost0.5 2.5 5.0

20K

1M

10M

CAN / TTCAN

LIN

25M

FlexRay 2.1

Safe-by-Wire

400MIDB-1394(Firewire)

Bit rate MOST50

(Twisted Pair)

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Alternative ArchitectureAlternative Architecture

Alternative architecture possible due to the new technologies

Features (Chassis control only):

Based on FlexRay and LIN

LIN for sensors

FlexRay for high speed integration

Shorter wiring to local ECUs

Reduced design complexity

Generic ECUs – Reduced cost

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Network Architecture of FutureNetwork Architecture of Future-- Many proposed uses of FlexRayMany proposed uses of FlexRay

FlexRayFlexRay

High speed backbone

X-by-Wire

Airbag deployment

LIN Sub BusLIN Sub Bus::

Doors

Seats etc.

CAN/TTCANCAN/TTCAN ––Applications:

Powertrain/body

TTCAN deterministic powertrain

MOSTMOSTInfotainment

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Time Triggered Network PrinciplesTime Triggered Network Principles

Communication based on Slots or Windows of time

Determinism

Message transmission time known

Schedule defined by a Matrix

m Windows x n Cycles

Message Scheduling Techniques:

TDMA

Mini-slotting

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Time Triggered Network PrinciplesTime Triggered Network Principles

Time Triggered Matrix for Schedule

Increasing Window or Slot Number

Free WindowFree WindowFree WindowMessage2Message1

Free WindowFree WindowMessage4Message3Message1

Free WindowFree WindowFree WindowMessage2Message1

Free WindowFree WindowFree WindowMessage3Message1

Message6Message5Message4Message2Message1

Increasing Cycle Number

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Time Triggered Network PrinciplesTime Triggered Network Principles

Time Division Media Access Scheduling Technique

In general:Messages are always transmitted in the appropriate slot

Increasing Window Number

Free WindowFree WindowFree WindowMessage2Message1

Free WindowFree WindowMessage4Message3Message1

Free WindowFree WindowFree WindowMessage2Message1

Free WindowFree WindowFree WindowMessage3Message1

Message6Message5Message4Message2Message1Increasing Cycle Number

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Time Triggered Network PrinciplesTime Triggered Network Principles

Mini-Slotting Scheduling Technique

Communication Cycle Length

Cycle 0 m+1 m+2Slot ID m

Cycle 1 m m+1 Slot ID m+2

Cycle 2 m+2m+1m

Duration of Mini-Slot depends upon whether or not frame transmission takes place

If transmission does not take place, then moves to next mini-slot

Message transmission will not take place if it cannot be completed within the Cycle Length

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Time Triggered Protocol CandidatesTime Triggered Protocol Candidates

Candidates that were considered include:

Time Triggered CAN

Byteflight

TTP

FlexRay

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Time Triggered CAN (TTCAN)Time Triggered CAN (TTCAN)

TDMA message scheduling techniques and Arbitration Windows

1Mbit/s

Single channel

Twisted Pair CAN Physical layer

No commercial examples

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ByteflightByteflight

Mini-slotting message scheduling technique

10Mbit/s

Single channel

8 bytes of data payload

BMW 7-Series (2001) – only production example

Airbag deployment, seatbelt restraint

Throttle and shift-by-wire

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Time Triggered Protocol (TTP)Time Triggered Protocol (TTP)

TDMA message scheduling technique

25Mbit/s and beyond

Dual channel for redundancy or faster transfer

244 byte data payload

No automotive commercial examples

Commercial examples:

Boeing 787 flight controls

Off highway drive-by-wire

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FlexRayFlexRay

TDMA and mini-slotting message scheduling technique

10Mbit/s

Dual channel for redundancy or faster transfer

254 byte data payload

Commercial examples:

BMW 2006 X5 for chassis controls

Audi next generation A8

Flight controls in development

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FlexRay Compared to CANFlexRay Compared to CAN

Many in developmentManySemiconductor Support

Twisted PairTwisted PairPhysical Layer

Specified, not developedNoneBus Guardian

2.5, 5, 10Mbit/sMax. 1Mbit/sBit rate

TDMA and mini-slotsCSMA-CD-NDBABus Access

15 bit Header CRC

24 bit Trailer CRC

15 bitCRC

Bus, Star, MixedBusNetwork Architecture

2548Data payload (bytes)

1111 and 29Message IDs (bits)

FlexRayCAN

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FlexRay Frame FormatFlexRay Frame Format

DLC (4)

End ofFrame

(7)

Identifier(11)

CRC (15)

Data(0 - 8 Bytes)

Standard CANSOF

Reserved (= ‘00’) CRC Delimiter

(1) Acknowledge Frame

(2)

RTR‘0’ = Data‘1’ = Request

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FlexRay and CAN Network TopologiesFlexRay and CAN Network Topologies

CAN Topologies• Linear Passive Bus:- Similar to current CAN bus

FlexRay Numerous topologies include:-• Passive Star:- Low cost star

• Active Star:- Fault tolerant star

• Linear Passive Bus:- Similar to current CAN bus

• Dual Channel Bus:- Dual redundancy

• Cascaded Active Star:- Multiple couplers

• Dual Channel Cascaded Active Star:-

• Additional safety

• Mixed Topology Network:-

• Mixture of Star and Bus topologies

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FlexRay Network AccessFlexRay Network Access

Time Triggered (64 cycles of continuous schedule)

FlexRay Network Access - static & dynamic segments

Static = Time Division Media Access

Dynamic = Mini-slotting

Node A

Node B

Node C

Bus

RD

RD

RD

t1 t2

RD

ID 1501

ID 1493

ID 2013

ID 1493

SOF

CAN Bus Access – CSMA-CD-NDBANDBA = Non Destructive Bitwise Arbitration

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FlexRay Static SegmentFlexRay Static Segment

Frames of static length assigned uniquely to slots of static duration• Frame sent when assigned slot matches slot counter

BG protection of static slots (when it is available)

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FlexRay Dynamic SegmentFlexRay Dynamic Segment

Dynamic bandwidth allocation• per node as well as per channel

Collision free arbitration via unique IDs and mini-slot counting• Frame sent when scheduled frame ID matches slot counter

No BG protection of dynamic slots

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Communication Example (3 Cycles) Communication Example (3 Cycles) Communication Cycle Length

Static Segment Dynamic Segment

Cycle 0 m+1 m+2Static Slot 0 Dynamic Slot ID mStatic Slot 1

Static Slot 0Cycle 1 Static Slot 1 m m+1 Dynamic Slot ID m+2

Cycle 2 m+2m+1mStatic Slot 0 Static Slot 1

Duration of Dynamic Slot depends upon whether or not frame tx or rx takes place

Each mini slot contains an Action Point (macroticks) when transmission takes place

If transmission does not take place, then moves to next mini-slot

Another 61 cycles and then back to Cycle 0 again

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Node Architecture Node Architecture -- Bus GuardianBus Guardian

• BD – Bus Driver• Electrical Physical layer

• BG – Bus Guardian• Protects message schedule

• Stops “Babbling Idiot” failure

CAN

None specified, could use proprietary implementation

FlexRay

Bus Guardian – specified but not developed

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FlexRay Physical LayerFlexRay Physical Layer

FlexRay – Twisted Pair (22metres@ 10Mbit/s)

CAN – Twisted Pair (40metres@ 1Mbit/s)

Electrical signals differ

Recessive Recessive

Vdiff

0 V

Dominant

CAN_High

VDiff2 V

CAN_Low

2.5 V

3.5 V

1.5 V

ISO 11898 CAN High Speed

Differential voltage uBus = uBP - uBM

Idle-LP is Power Off situation. BP and BM at GND.

Idle is when no current is drawn but BP & BM are biased to the same voltage level

Data_1, BP at +ve level, BM at -ve level, Differential = +ve

Data_0, BM is +ve level, BP is -ve level, Differential = -ve

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FlexRay Voltage Levels FlexRay Voltage Levels –– In PracticeIn Practice

The FlexRay PL has a buffer supplied by VBuf(typically ~5v)

The idle level is half VBuf

Typically around 2.5 volts

Red shows BP

Green shows BM

At startup - Shows rise from Idle_LP to Idle

FlexRay Application: BMWFlexRay Application: BMW

Latest BMW X5Latest BMW X5

5 5 ECUsECUs for Adaptive Drive for Adaptive Drive –– Electronic Electronic damper controldamper control

Wheel located Wheel located ECUsECUs

Management unit acts as Active StarManagement unit acts as Active Star

Audi have announced new A8 with FlexRayAudi have announced new A8 with FlexRay

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SAPECS (2004 to 2007)SAPECS (2004 to 2007)((SSecured ecured AArchitecture & rchitecture & PProtocols for rotocols for EEnhanced nhanced CCar ar SSafety)afety)

Objectives

• Capture Requirements of :-• information around vehicle

• telematic information between vehicle & infrastructure

• FlexRay Demo• Develop and integrate FlexRay IP for demo

• Demo of power train control

• Analysis / Qualification tool for displaying data

• Qualification standards for systems• Review of current

• Suggestion of new procedures and tools for qualification

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SAPECS SAPECS -- Partner InputsPartner Inputs

Design, Analysis and automatic FlexRay stack configuration tools

Warwick Control

Engine management demonstratorValeo

Capture requirements for vehicle & telematic information

CS

FlexRay software stack developmentAyrton Technology

FlexRay microcontroller with fail-safety functionality development

Atmel Nantes

FlexRay physical layer developmentAMI Semiconductors

ContributionCompany

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SAPECS FlexRay DemonstratorSAPECS FlexRay Demonstrator

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SAPECS FlexRay DemonstratorSAPECS FlexRay DemonstratorElectronic Throttle Motor controlled by Electronic Pedal Sensor via the Engine ECU

ECUs connected to a Dual Channel FlexRay bus

Distributed Architecture with THREE calculators:

Pedal

• 3 ECUs - majority voter calculates position at Engine ECU

Throttle

• receives new position from Engine ECU

• turns position info into H bridge control data.

Engine Management (Main)

• Performs standard engine management along with throttle control

• Receive pedal position data from the three Pedal ECUs to perform the majority voter strategy.

• Transfers the new position to the Throttle ECU.

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SAPECS FlexRay Communication SAPECS FlexRay Communication ––Development ProcessDevelopment Process

Requirements

C- Coding

DesignCode Test

Validation

FlexRay Planning

Tool(Prototype of future

NetGen, X-Editor)

FlexRay Code Configuration

Tool

FlexRay Network Analyser

XML Configuration

File

FlexRay Interface Card

Node Under Development

FlexRay database

FlexRay Node

FlexRay Node

FlexRay Node

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Other Emerging Network TechnologiesOther Emerging Network Technologies

Safe-by-Wire Plus

Safe-by-Wire Plus consortium formed in February 2004

Automotive safety bus for occupant safety applications (e.g. airbag deployment and seat belt restraint)

Safe-by-Wire Plus has variable bus speeds of 20, 40, 80 or 160 kbps

Expected to have a similar nodal cost comparable to CAN

The application of the Safe-by-Wire protocol is narrow and therefore is not suitable for general network service

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Emerging StandardsEmerging Standards

Network data exchange:

CANdbVector proprietary

LDF (LIN Description Files) Open standard

LIN only

FIBEXNew open ASAM standard

CAN, LIN, MOST, FlexRay

For diagnostics/analysis tools

AUTOSAR (CAN, LIN, MOST, FlexRay) For ECU designers

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Summary and OutlookSummary and Outlook

CANCAN

original aim: reduction wiring harness complexity, size and weight

However, successful adoption has allowed integration of many more ECUs

Led to more wiring, more CAN buses, more gateways etc.

FlexRayFlexRay

off-the-shelf technology available for applications in which CAN performance has limitations and has been compared with CAN

FlexRay implemented in the BMW X5 plus numerous other emerging applications

Likely to become de-facto standard for X-by-Wire and future high speed networking

Protocol features likely to evolve further

Danger is that FlexRay will allow the growth in vehicle electronics to explode

Extremely complex when compared to CAN!!!!!!!!