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!!!!!!!!