FlexRay and Automotive Networking Future

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FlexRay and Automotive Networking Future
Chris QuigleyWarwick Control Technologies
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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

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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

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

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Emerging Networks - Nodal Costing
Bit rate
MOST50 (Twisted Pair)?
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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
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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

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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

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Time Triggered Network Principles

• Time Triggered Matrix for Schedule

Increasing Window or Slot Number
Increasing Cycle Number
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Time Triggered Network Principles

• Time Division Media Access Scheduling Technique

In general Messages are always transmitted in
the appropriate slot
Increasing Window Number
Increasing Cycle Number
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Time Triggered Network Principles
Mini-Slotting Scheduling Technique
Communication Cycle Length
m1
m2
Cycle 0
Slot ID m
Cycle 1
m1
m
Slot ID m2
Cycle 2
m2
m1
m
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 Candidates

• Candidates that were considered include
• Time Triggered CAN
• Byteflight
• TTP
• FlexRay

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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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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

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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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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

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FlexRay Compared to CAN
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FlexRay Frame Format
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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

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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

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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)?

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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

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Communication Example (3 Cycles)
Communication Cycle Length
Static Segment
Dynamic Segment
Cycle 0
Static Slot 0
m1
m2
Static Slot 1
Dynamic Slot ID m
Cycle 1
Static Slot 0
Static Slot 1
m1
m
Dynamic Slot ID m2
Cycle 2
m2
m1
m
Static 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 - 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

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FlexRay Physical Layer

• FlexRay Twisted Pair (22metres_at_ 10Mbit/s)?
• CAN Twisted Pair (40metres_at_ 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
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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
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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

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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

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SAPECS - Partner Inputs
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SAPECS FlexRay Demonstrator
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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.

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SAPECS FlexRay Communication Development Process

Validation
Requirements
FlexRay database
FlexRay Network Analyser
XML Configuration File
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
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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

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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

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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!!!!!!!!