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FlexRay and Automotive Networking Future

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1 FlexRay and Automotive Networking Future
Chris Quigley Warwick Control Technologies

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

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

4 Why FlexRay? – CAN Latency
Typical CAN bus characteristic – unpredictable latency Typical TT network characteristic – predictable latency Message Latency Message Latency Bus Load Bus Load

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

6 Emerging Networks - Nodal Costing
TTP/C MOST25 (Optical)‏ FlexRay II Relative Cost 0.5 2.5 5.0 20K 1M 10M CAN / TTCAN LIN 25M FlexRay 2.1 Safe-by-Wire 400M IDB-1394 (Firewire)‏ Bit rate MOST50 (Twisted Pair)‏

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

8 Network Architecture of Future - Many proposed uses of 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

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

10 Time Triggered Network Principles
Time Triggered Matrix for Schedule Increasing Window or Slot Number Free Window Message2 Message1 Message4 Message3 Message6 Message5 Increasing Cycle Number

11 Time Triggered Network Principles
Time Division Media Access Scheduling Technique In general: Messages are always transmitted in the appropriate slot Increasing Window Number Free Window Message2 Message1 Message4 Message3 Message6 Message5 Increasing Cycle Number

12 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

13 Time Triggered Protocol Candidates
Candidates that were considered include: Time Triggered CAN Byteflight TTP FlexRay

14 Time Triggered CAN (TTCAN)‏
TDMA message scheduling techniques and Arbitration Windows 1Mbit/s Single channel Twisted Pair CAN Physical layer No commercial examples

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

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

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

18 FlexRay Compared to CAN
Many in development Many Semiconductor Support Twisted Pair Physical Layer Specified, not developed None Bus Guardian 2.5, 5, 10Mbit/s Max. 1Mbit/s Bit rate TDMA and mini-slots CSMA-CD-NDBA Bus Access 15 bit Header CRC 24 bit Trailer CRC 15 bit CRC Bus, Star, Mixed Bus Network Architecture 254 8 Data payload (bytes)‏ 11 11 and 29 Message IDs (bits)‏ FlexRay CAN

19 FlexRay Frame Format Standard CAN 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

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

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

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)‏

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

24 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 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

25 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

26 FlexRay Physical Layer
FlexRay – Twisted Pair 10Mbit/s)‏ CAN – Twisted Pair 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 Recessive Vdiff 0 V Dominant CAN_High VDiff 2 V CAN_Low 2.5 V 3.5 V 1.5 V ISO CAN High Speed

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

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

29 SAPECS (2004 to 2007) (Secured Architecture & Protocols for Enhanced Car Safety)
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

30 SAPECS - Partner Inputs
Design, Analysis and automatic FlexRay stack configuration tools Warwick Control Engine management demonstrator Valeo Capture requirements for vehicle & telematic information CS FlexRay software stack development Ayrton Technology FlexRay microcontroller with fail-safety functionality development Atmel Nantes FlexRay physical layer development AMI Semiconductors Contribution Company

31 SAPECS FlexRay Demonstrator

32 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.

33 SAPECS FlexRay Communication – Development Process
Validation Requirements FlexRay database XML Configuration File FlexRay Network Analyser FlexRay Planning Tool (Prototype of future NetGen, X- Editor)‏ Code Test Design FlexRay Interface Card FlexRay Code Configuration Tool C- Coding Node Under Development FlexRay Node FlexRay Node FlexRay Node

34 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 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

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

36 Summary and Outlook CAN FlexRay
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!!!!!!!!

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