FlexRay and Automotive Networking Future Chris Quigley Warwick Control Technologies
Presentation Overview High Speed and High Integrity Networking Why FlexRay? CAN Problems Time Triggered Network Principles Time Triggered Protocol Candidates FlexRay protocol and Applications: BMW, Audi, SAPECS Other Emerging Protocols and Standards Summary 2
Why FlexRay? CAN is extremely cost effective and powerful technology However, for more intensive applications, it is reaching its limit CAN Problems Unpredictable 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 3
Why FlexRay? CAN Latency Typical CAN bus characteristic unpredictable latency Typical TT network characteristic predictable latency Message Latency Message Latency Bus Load Bus Load 4
Why FlexRay? Complicated 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 5
Emerging Networks - Nodal Costing 400M IDB-1394 (Firewire) 25M Bit rate MOST50 (Twisted Pair) TTP/C MOST25 (Optical) 10M FlexRay II FlexRay 2.1 1M CAN / TTCAN 20K LIN Safe-by-Wire 0.5 2.5 5.0 Relative Cost 6
Alternative 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 7
Network Architecture of Future - Many proposed uses of FlexRay FlexRay High speed backbone X-by-Wire Airbag deployment LIN Sub Bus: Doors Seats etc. CAN/TTCAN Applications: Powertrain/body TTCAN deterministic powertrain MOST Infotainment 8
Time 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 9
Time Triggered Network Principles Time Triggered Matrix for Schedule Increasing Window or Slot Number Increasing Cycle Number Message1 Message1 Message2 Message3 Message4 Message5 Message6 Message1 Message2 Message1 Message3 Message4 Message1 Message2 10
Time Triggered Network Principles In general: Time Division Media Access Scheduling Technique Messages are always transmitted in the appropriate slot Increasing Window Number Increasing Cycle Number Message1 Message1 Message1 Message2 Message3 Message2 Message4 Message5 Message6 Message1 Message3 Message4 Message1 Message2 11
Time Triggered Network Principles Mini-Slotting Scheduling Technique Communication Cycle Length Cycle 0 Slot ID m m+1 m+2 Cycle 1 m m+1 Slot ID m+2 Cycle 2 m m+1 m+2 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 12
Time Triggered Protocol Candidates Candidates that were considered include: Time Triggered CAN Byteflight TTP FlexRay 13
Time Triggered CAN (TTCAN) TDMA message scheduling techniques and Arbitration Windows 1Mbit/s Single channel Twisted Pair CAN Physical layer No commercial examples 14
Byteflight 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 15
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 16
FlexRay 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 17
FlexRay Compared to CAN Message IDs (bits) Data payload (bytes) Network Architecture CRC Bus Access Bit rate Bus Guardian Physical Layer Semiconductor Support CAN 11 and 29 8 Bus 15 bit CSMA-CD-NDBA Max. 1Mbit/s None Twisted Pair Many FlexRay 11 254 Bus, Star, Mixed 15 bit Header CRC 24 bit Trailer CRC TDMA and mini-slots 2.5, 5, 10Mbit/s Specified, not developed Twisted Pair Many in development 18
FlexRay Frame Format SOF RTR 0 = Data 1 = Request Identifier (11) Reserved (= 00 ) CRC Delimiter (1) DLC (4) Data (0-8 Bytes) CRC (15) Acknowledge Frame (2) End of Frame (7) Standard CAN 19
FlexRay 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 20
FlexRay Network Access CAN Bus Access CSMA-CD-NDBA NDBA = Non Destructive Bitwise Arbitration Time Triggered (64 cycles of continuous schedule) FlexRay Network Access - static & dynamic segments Static = Time Division Media Access Node A ID 1493 SOF t1 t2 R D Dynamic = Mini-slotting Node B ID 1501 Node C ID 2013 R D R D Bus ID 1493 R D 21
FlexRay 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) 22
FlexRay 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 23
Communication Example (3 Cycles) Communication Cycle Length Static Segment Dynamic Segment Cycle 0 Static Slot 0 Static Slot 1 Dynamic Slot ID m m+1 m+2 Cycle 1 Static Slot 0 Static Slot 1 m m+1 Dynamic Slot ID m+2 Cycle 2 Static Slot 0 Static Slot 1 m m+1 m+2 Duration of Dynamic Slot depends upon whether or not frame tx or rx takes place Another 61 cycles and then back to Cycle 0 again Each mini slot contains an Action Point (macroticks) when transmission takes place If transmission does not take place, then moves to next mini-slot 24
Node Architecture - Bus Guardian CAN None specified, could use proprietary implementation FlexRay Bus Guardian specified but not developed BD Bus Driver Electrical Physical layer BG Bus Guardian Protects message schedule Stops Babbling Idiot failure 25
FlexRay Physical Layer FlexRay Twisted Pair (22metres@ 10Mbit/s) CAN Twisted Pair (40metres@ 1Mbit/s) Electrical signals differ 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 ISO 11898 CAN High Speed Recessive Dominant Recessive 3.5 V 2.5 V 1.5 V CAN_High V Diff 2 V CAN_Low V diff 0 V 26
FlexRay Voltage Levels In Practice The FlexRay PL has a buffer supplied by VBuf (typically ~5v) The idle level is half VBuf Typically around 2.5 volts At startup - Shows rise from Idle_LP to Idle Red shows BP Green shows BM 27
FlexRay Application: BMW Latest BMW X5 5 ECUs for Adaptive Drive Electronic damper control Wheel located ECUs Management unit acts as Active Star Audi have announced new A8 with FlexRay
SAPECS (2004 to 2007) (Secured Architecture & Protocols for Enhanced Car Safety) 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 29
SAPECS - Partner Inputs Company AMI Semiconductors Contribution FlexRay physical layer development Atmel Nantes Ayrton Technology FlexRay microcontroller with fail-safety functionality development FlexRay software stack development CS Valeo Capture requirements for vehicle & telematic information Engine management demonstrator Warwick Control Design, Analysis and automatic FlexRay stack configuration tools 30
SAPECS FlexRay Demonstrator 31
SAPECS FlexRay Demonstrator Electronic 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. 32
SAPECS FlexRay Communication Development Process Requirements FlexRay database Validation FlexRay Planning Tool XML Configuration File FlexRay Network Analyser (Prototype of future NetGen, X- Editor) Design FlexRay Code Configuration Tool Code Test FlexRay Interface Card C- Coding Node Under Development FlexRay Node FlexRay Node FlexRay Node 33
Other 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 34
Emerging Standards Network data exchange: CANdb Vector proprietary LDF (LIN Description Files) Open standard LIN only FIBEX New open ASAM standard CAN, LIN, MOST, FlexRay For diagnostics/analysis tools AUTOSAR (CAN, LIN, MOST, FlexRay) For ECU designers 35
Summary and Outlook CAN 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. FlexRay 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!!!!!!!! 36