introduction to automotive networks

Introduction to Automotive Networks An introduction to: CAN, LIN, MOST and Flexray

Agenda • Evolution of in-vehicle automotive Networks – Why were automotive networks introduced? – What are automotive networks used for?

• Basic introduction to networking principles • Current and future networking technologies – CAN, LIN, MOST, Flexray

General Computer Networks •Interconnected devices that store, retrieve and share information

Automotive Network Evolution - 1

ECU = Electronic Control Unit

Automotive Networking Evolution - 2

Hard-wired Integration ECU = Electronic Control Unit

Automotive Networking Evolution - 3

Data Bus Integration ECU = Electronic Control Unit

Automotive Networking - advantages • Reduced wiring harness weight – lower emissions, improved fuel consumption

• Reduction in number of redundant sensors & connectors • Improved reliability – fewer warranty issues • Improved diagnostics • Eases integration of more ECU’s – Standard interfaces

Legacy and current networking technologies •In-Vehicle Network Protocols Legacy Powertrain / Chassis Body

SCP, K-bus

Infotainment D2B

Current

Future

CAN

CAN, FlexRay

CAN, LIN

CAN, LIN, FlexRay

MOST Gen 2.1

Ethernet (BroadR-Reach)

Why so many different types of networks? Data rate

Comparison : Network data rate versus relative communication costs per node

(bps)

MOST

25M

Optical

10M

Flexray Optical/

1M

Copper

CAN 125K 20K

Dual wire

LIN

Relative communication cost per node

Single wire

0.5

1

2.5

5

Multiple networks and gateways

Multiple-Bus Networking

Head Lights

Low Speed CAN

High Speed CAN

ABS

Tail Lights

Dash Board

Doors

Engine Control Gateway

Suspension Control

Controller Area Network (CAN) Overview

CAN

CAN Network History & Evolution •Developed by Bosch in Europe – At request of BMW and Mercedes

•History and Evolution of CAN Network protocol – 1991 CAN – 1992 – 1999 – 2003 – 2003

– ISO/Draft International Standard + Extended – – – –

First use in car (S-series, BMW 8) estimated 125 million nodes world-wide estimated 240 million nodes world-wide ISO 11898 revised

•Used by almost all car manufacturers for the main data communications technology

CAN “physical layer” – Hardware Input/Output Ports

Input/Output Ports

Microcontroller eg. 80537

Microcontroller eg. 68705 Microcontroller eg. 68HC05X4

CAN Controller e.g. 82C200 TX0 TX1

CAN Controller e.g. 82527

RX0 RX1

TX0 TX1

CAN Transceiver CAN_L

RX0 RX1

CAN Transceiver

CAN_H

CAN_H

T w i sted - p ai r W i re

CAN_L

CAN “physical layer” – CAN Signalling •Bit Representation – CAN uses an electrical medium to transfer data – UTP (Unshielded Twisted Pair) – Data represented by voltage difference between two wires • CAN_High – Recessive = 2.5V – Dominant = 3.5V • CAN_Low – Recessive = 2.5V – Dominant = 1.5V

V 3.5 V

2.5 V

Can_H

0 1 0 1 0 1 0

1.5 V

Can_L t

CAN Signalling Logical ‘1’ = Vdiff = 0V Logical ‘0’ = Vdiff = 2V

CAN “physical layer” – Twisted pair wiring Transient noise

CAN-HI

Receiver looks for a 2V differential CAN-LO

CAN “physical layer” – Bus topology •CAN Physical Layer – Realities: JLR + J2284 (SAE) Node 1 120Ώ

Node 2

Node n Node 3

120Ώ

CAN_H CAN_L Automotive constraints are quite different from the original theoretical specification

CAN Data Rate 500 Kbps 250 Kbps 125 Kbps

CAN Bus Length 33.5 m* 50 m 50 m

Stub Length 1m 1m 1m

Max Nodes 16* 32 32

*Note. 5m + 1node required for test equipment access => max length from J1962 connector to terminator = 28.5m

CAN “physical layer” – Bus topology •Example – Physical implementation of CAN bus schematic

CAN “physical layer” – Bus topology •Example – Physical implementation of CAN bus schematic

CAN “data link layer” – CAN message frame •CAN Data is transferred in frames 1 Bit 6 Bits 1 ... 8 Bits bytes

11 or 29

15 1 Bit 7 1 Bit 1Bit Bits Bits

>=3 Bits

End of Frame ACK Delimiter ACK ACK Slot CRC Delimiter

CRC Sequence Data Field Control (2 bits reserved for future, DLC0-3 is the data length code )

{

1 Bit

Interframe Space

{

Interframe Space

RTR Bit Identifier Start of Frame

Arbitration Field

RTR = Remote Transmission Frame CRC = Cyclic Redundancy Check ACK = Acknowledge DLC = Data Length Code

CAN “data link layer” – Bus Access •Access to the CAN network

– Multiple bus masters - every node attempts to transmit when it wants to… – Every node must contend (arbitrate) for network access

•Bus Access is achieved through CSMA/CD with NDBA •Carrier Sense Multiple Access/Collision Detect – Allows multiple access to transmission medium – Used in Ethernet, CAN etc.

•Non-Destructive Bit-wise Arbitration

– Fixed priority scheme (based on node ID) – If node senses a higher priority node is requesting bus access it relinquishes bus – Highest priority node always granted access – No corrupted message during arbitration - No wasted bandwidth – Guaranteed throughput of high priority messages

Automotive Networking CAN bus Overview •CAN Data Link Layer – How CSMA/CD & NDBA t1 t2 works SOF R Node A 0 1 0 1 1 1 1 1 0 ID 1493 D (5D5Hex) R D

Node B ID 1501 (5DDHex)

R D

Node C ID 2013 (7DDHex)

R D

Bus ID 1493 (5D5Hex)

t1 & t2 , Node C and Node B lost arbitration

CAN Network – Bus Load & Message Latency •CAN networks are non-deterministic – No guarantees on time to deliver a message – Does not perform well above 50% bus loading – 35-40% is the usual practical bus loading limit Typical CAN bus characteristic Message Latency

Bus Load

CAN Network Summary •Features – Low cost, twisted-pair (2-wire) electrical implementation – Multiple bus masters - arbitration used to grant access to network – 125 & 500kbits/sec – Non-deterministic

•Where used – High speed - PowerTrain – Low/Medium speed – Body Control Systems

Local Interconnect Network (LIN) Overview

LIN Network overview • Not a competitor or alternative to CAN – Introduced in 2000 – Low cost / lower bandwidth – Developed for intelligent sensor and actuator applications – Automotive Sub-bus (UART based), CAN bus complement

• Where used – Switches, Solenoids, Actuators and Motors (mechatronics) – Bodywork, Doors etc.

LIN applications

LIN “physical layer – Signalling •Data Representation – LIN uses an electrical medium to transfer data – A simple single wire interconnect (based on enhanced ISO 9141) – Data represented simply by voltage on wire – 12 volts = Logic 1, 0 volts = Logic 0

• Speed

12V=logic 1

– Low speed - 20Kbaud – Limited for EMC reasons

0V=logic 0

LIN Bus Architecture – master/slave LIN Master Message Header

Possibly to vehicle body control CANbus

Message Response

LIN Bus

LIN Slave

LIN Slave

LIN Slave

Message Response

Message Response

Message Response

LIN “data link layer” – LIN message frame •LIN data is transferred in frames

Produced by Master

Produced by Master or Slave

LIN “data link layer” – Bus access Access to the LIN network Single Master – no arbitration necessary Master determines transmission using task schedule – Predictable message timing as everything works to the master schedule – Slaves respond to master request

LIN Network Summary •Features – – – –

Low cost, single-wire implementation (UART) Single Master, Multiple Slaves Low bandwidth - 20kbaud Complements CAN bus – not a replacement

•Where used – Switches, Solenoids, Actuators and Motors (mechatronics) – Bodywork, Doors etc.

Media Orientated Systems Transport (MOST) Network Overview

MOST Network History • A network was required to link modular multi-media systems

– Ability to transmit audio signals as well as control – Audio signals are typically twisted pair wiring, can be 9+ audio sources = wiring complexity issues – AM/FM radio, CD, DVD, Satellite radio, Navigation, Phone, Voice, TV, Auxiliary input

• Ability to seamlessly control several sources • Need to share large amounts of data

– Phone book (phone to navigation display) – Traffic messages (radio to navigation display) – Station data (Satellite radio to navigation display)

• Ease of upgrade (not quite plug & play) • MOST was developed & controlled by industry consortium – Used by JLR, Volvo, BMW, Mercedes, GM……

MOST Physical Layer – Network layer 1 • Data representation – – – –

MOST uses an optical medium to transfer data Plastic Optical Fibre (POF) Ring topology Data represented by presence or absence of light

• Speed – Up to 25Mbits/sec

MOST “data link layer” – Types of MOST messages •MOST Data is transferred in network frames which can contain three types of data: • Synchronous data – Guaranteed bandwidth with minimal buffering – Real-time transmission e.g. streaming audio & video files

• Asynchronous data – Variable throughput – For transmission of ‘large’ packet data e.g. computer files, Sat-Nav maps, web pages etc.

• Control Data – Transportation of Commands, Status and “small” Packet Data

MOST Frame Data •Two examples ONE NETWORK FRAME = 512 bits (64 bytes) MAX BANDWIDTH ALLOCATED TO ASYNCHRONOUS CHANNELS = 36 bytes 0

63

Audio – CD, Radio

Data – phone book download, traffic info

24 bytes

36 bytes

0

63

Audio – CD, Radio, DVD, Phone, satellite radio, i-Pod 60 bytes 1-60

0 0

SOURCE DATA CHANNELS (Asynchronous and/or Synchronous) BOUNDARY DESCRIPTOR PREAMBLE

= Asynchronous Channel

CONTROL CHANNEL FRAME CONTROL & STATUS PARITY CHECK

= Synchronous Channel

= Boundary Descriptor

61-62 63 63

MOST “data link layer” – Bus Access • Access to the MOST network • Single network master device – the timing master • Time Division Multiplexing – Time slots provide predictable performance – Bandwidth can be varied by allocating bytes to logical channels

MOST Network Summary •Features – Single Plastic Optical Fibre, Ring topology – Good EMC characteristics (immunity & emissions) – High speed for digital audio & video (low cost per Mhz) – Asynchronous (14.4Mbps), Synchronous (23Mbps) data – Plug & Play Applications for up to 64 devices

•If ring is broken everything fails •Where used – Designed for Multi-media applications (also known as Infotainment) in the automotive environment

Future Automotive Networks

Future Automotive Networks Industry pressures: • Move to drive-by-wire applications – Safety-critical, robust, fault-tolerant – More sophisticated control strategies • Hybrid/EV vehicles

• Faster speeds – Increased bandwidth • More ECU’s, more sensors • Higher volumes of data to move around the vehicle – Faster response times • Hybrid vehicle electric motor control

Networking – Message Latency Typical TT network characteristic – predictable latency

Typical CAN bus characteristic – unpredictable latency

Message Latency

Message Latency

Bus Load

Bus Load

FlexRay is a time-triggered (TT) protocol – each node is guaranteed access to the bus

FlexRay Physical Layer •

•

FlexRay • Electrical, Twisted Pair • 22metres@ 10Mbit/s

•

Idle-LP : Power Off situation. BP & BM @ GND. Idle : No current is drawn, BP & BM biased to the same voltage level

CAN •

Differential voltage uBus = uBP - uBM

Electrical, Twisted Pair (40metres@ 1Mbit/s)

Data_1, BP +ve, BM –ve, Differential = +ve Data_0, BM +ve, BP -ve, Differential = -ve

FlexRay Physical Layer

FlexRay Data Link Layer

TDMA Access

Note: FlexRay is much more complex than CAN to design – there are multiple design parameters to consider. Consider integration issues as well.

FlexRay Networking  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 Many proposed uses of FlexRay

Review of what we’ve learnt • Networking principles – “physical layer” – how data is represented – “data link layer” – how data is transferred between nodes

• Evolution of automotive networks – Why they were introduced

• Current Network Technologies – CAN, LIN, MOST – Choice depends upon application requirements, speed, cost etc.

• Future Network Technologies – FlexRay (one possible solution)