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FlexRay and Automotive Networking Future Chris Quigley Warwick Control Technologies Slide 2 2 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 Slide 3 3 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 Slide 4 4 Why FlexRay? CAN Latency Bus Load Message Latency Typical CAN bus characteristic unpredictable latency Bus Load Message Latency Typical TT network characteristic predictable latency Slide 5 5 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 Slide 6 6 Emerging Networks - Nodal Costing TTP/C MOST25 (Optical) FlexRay II Relative Cost 0.52.55.0 20K 1M 10M CAN / TTCAN LIN 25M FlexRay 2.1 Safe-by-Wire 400M IDB-1394 (Firewire) Bit rate MOST50 (Twisted Pair) Slide 7 7 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 Slide 8 8 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 CAN/TTCAN Applications: Powertrain/body TTCAN deterministic powertrain MOST MOST Infotainment Slide 9 9 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 Slide 10 10 Time Triggered Network Principles Time Triggered Matrix for Schedule Free Window Message2Message1 Free Window Message4Message3Message1 Free Window Message2Message1 Free Window Message3Message1 Message6Message5Message4Message2Message1 Increasing Window or Slot Number Increasing Cycle Number Slide 11 11 Time Triggered Network Principles Time Division Media Access Scheduling Technique Free Window Message2Message1 Free Window Message4Message3Message1 Free Window Message2Message1 Free Window Message3Message1 Message6Message5Message4Message2Message1 Increasing Window Number Increasing Cycle Number In general: Messages are always transmitted in the appropriate slot Slide 12 12 Cycle 0 Cycle 1 Slot ID m Mini-Slotting Scheduling Technique Cycle 2 m+1mSlot ID m+2 Communication Cycle Length m+1m+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 Time Triggered Network Principles Slide 13 13 Time Triggered Protocol Candidates Candidates that were considered include: Time Triggered CAN Byteflight TTP FlexRay Slide 14 14 Time Triggered CAN (TTCAN) TDMA message scheduling techniques and Arbitration Windows 1Mbit/s Single channel Twisted Pair CAN Physical layer No commercial examples Slide 15 15 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 Slide 16 16 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 Slide 17 17 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 Slide 18 18 FlexRay Compared to CAN Many in developmentManySemiconductor Support Twisted Pair Physical 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 Slide 19 19 FlexRay Frame Format DLC (4) End of Frame (7) Identifier (11) CRC (15) Data (0 - 8 Bytes) Standard CAN SOF Reserved (= 00) CRC Delimiter (1) Acknowledge Frame (2) RTR 0 = Data 1 = Request Slide 20 20 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 Slide 21 21 FlexRay Network Access Time Triggered (64 cycles of continuous schedule) FlexRay Network Access - static & dynamic segments Static = Time Division Media Access Dynamic = Mini-slotting CAN Bus Access CSMA-CD-NDBA NDBA = Non Destructive Bitwise Arbitration Slide 22 22 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) Slide 23 23 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 Slide 24 24 Communication Example (3 Cycles) Cycle 0 Static Slot 0 Static Slot 1 Cycle 1 Dynamic Slot ID m Static Segment Dynamic Segment Static Slot 0 Static Slot 1 Another 61 cycles and then back to Cycle 0 again Cycle 2 Static Slot 0Static Slot 1 m+1mDynamic Slot ID m+2 Communication Cycle Length m+1m+2 m m+1 m+2 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 Slide 25 25 Node Architecture - Bus 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 Slide 26 26 FlexRay Physical Layer FlexRay Twisted Pair (22metres@ 10Mbit/s) CAN Twisted Pair (40metres@ 1Mbit/s) Electrical signals differ Recessive V diff 0 V Dominant CAN_High V Diff 2 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 Slide 27 27 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 Red shows BP Green shows BM At startup - Shows rise from Idle_LP to Idle Slide 28 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 Slide 29 29 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 SAPECS (2004 to 2007) (Secured Architecture & Protocols for Enhanced Car Safety) Slide 30 30 SAPECS - Partner 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 Slide 31 31 SAPECS FlexRay Demonstrator Slide 32 32 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. SAPECS FlexRay Demonstrator Slide 33 33 SAPECS FlexRay Communication Development Process Requirements C- Coding Design Code Test Validation FlexRay Planning Tool (Prototype of future NetGen, X- Editor) FlexRay Code Configuration Tool FlexRay Network Analyser XML Configuration File FlexRay Node FlexRay Interface Card Node Under Development FlexRay database Slide 34 34 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 Other Emerging Network Technologies Slide 35 35 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 Slide 36 36 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!!!!!!!! Summary and Outlook