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www.vector.com 7.0 Vector – Automotive. Embedded. Engineering.
V
Dear Reader,

There’s no better medium for having your
challenges taken up than qualified articles in
professional journals. Presenting current
problems and their solutions is just as important
an issue to us as discussing technical principles
and standards. Experts at Vector address your
questions and concerns and develop real-world
solutions from them.
In the seventh edition collection of Vector
technical articles, we cover current issues from
AUTOSAR Adaptive, the tense field of security
and safety and new developments to automated
driving and much more in 27 new articles.
We hope you’re looking forward to some very
inspiring articles!
Stuttgart, July 2018 Dr. Thomas Beck
Status: July 2018
Responsible for content: Vector Informatik GmbH, Stuttgart
All mentioned product names are either registered or nonregistered brand names of their respective owners.
Continual global availability of all products or services is not guaranteed.
Errors and omissions reserved.
Reprint only permitted with written approval of Vector Informatik GmbH, Stuttgart.
Please note: Some of the web links given in this article may be obsolete.
They were valid at the time of first publication of the technical article.
Illustration & Design: Cirek Mediendesign, Stuttgart, Germany
Contents
Company Profile Vector – The Company Design and Optimization of E/E Architectures 2/10
PREEvision as Model-Based Tool for the Next Generation
Serial Bus Systems Data Communication in the Automobil Part 1 1/0
E/E Development for Future Vehicle Innovations 2/16
Architecture, Tasks, and Advantages of Serial Bus Systems
An Integrated, Model-based Approach
Serial Bus Systems – CAN Data Communication in the Automobil Part 2 – CAN 1/6
Integrated Development of a Complete E/E Architecture 2/26
CAN Gets Even Better 1/12 Reaching Goals Reliably Using a Model-Based Approach
Ways to Transition from Classic CAN to the Improved CAN FD
Service-oriented Architectures and Ethernet in Vehicles 2/30
CAN FD: Fast Measurement and Reprogramming 1/16 Towards Data Centers on Wheels with Model-based Methods
Eye Diagram Analysis for CAN FD 1/20 Model-based Solutions for Medical Systems 2/36
Fast identification of poor signal quality An Integrated Approach for the E/E Development Process
CAN Tools – Then and Now 1/24 Integrated Requirement Management 2/42
The Next Stage in the Evolution of Requirement Engineering
Serial Bus Systems – LIN Data Communication in the Automobil Part 3 – LIN 1/28
Serial Bus Systems – FlexRay Data Communication in the Automobil Part 4 – FlexRay 1/34 Testing Current Approaches for ECU Testing 3/0
What Really Matters
Serial Bus Systems – Wireless Analysis in a Multi-Protocol CAN Environment 1/40
Automotive Ethernet Quickly Converting Test Benches Worldwide in Record Time 3/4
Acquiring Bus Data Wirelessly from Multiple Vehicles 1/44
Record-Breaking
Top-notch Precision Despite the “Air Interface”
Network Tests for Everyone 3/8
IP and Ethernet in Motor Vehicles 1/50
With Minimum Configuration Effort for Maximum Testing Depth
Challenges for the Development Tool, Illustrated by Today’s Applications
Case Study: Fraunhofer 3/13
Challenge of Ethernet Use in the Automobile 1/56
Flexible Interfaces and Software Tools Simplify ECU Development Tips and Tricks for the Use of CAPL 3/14
Part 1: CAPL Basics
New Perspectives on Remaining Bus Simulation for Networks with SOME/IP 1/62
Validating Automotive IP Network Elements Tips and Tricks for the Use of CAPL 3/16
Part 2: Effectively Apply CAPL
AUTOSAR Learns Ethernet 1/66
Tips and Tricks for the Use of CAPL 3/18
New Communication Paradigms in Automotive Networking 1/70
Part 3: CAPL for Advanced Users
Ethernet and CAN FD are the New Trailblazers
Quick Paths to a Comprehensive Remaining Bus Simulation 3/20
Full Transparency with Automotive Ethernet 1/76
Creative Virtual Networks Without Programming Expertise
Finally Seeing what is Really Happening
Hardware Simulation for the Challenging Unimog Tire Pressure Control System 3/24
Time Synchronization in Automotive Ethernet Networks 1/82
Time Savings and New Options by ECU Tests on the Model
Balancing Act Between AUTOSAR, IEEE, and TSN
ECU Testing with XCP Support 3/28
The Future with SOA, POSIX, TSN 1/88
A Look Behind the Scenes
Automotive Ethernet: Trends and Challenges
Case Study: GETRAG 3/31
From Signal to Service 1/94
Challenges for the Development of AUTOSAR Adaptive Applications Flexible Test Systems for Efficient ECU Testing 3/32
Functional Testing with Error Simulation at the Developer’s Bench
Serial Bus Systems – ITS-G5 Testing Car2x Applications 1/100
Requirements for Test Tools Based on Example of the Road Works Warning Functional GUI Testing of In-vehicle Infotainment Systems in Virtual 3/36
and Real Environments
Car2x – From Research to Product Development 1/104
How Automotive OEMs and Suppliers are Successfully Completing What Kinds of Interfaces are Available? 3/40
Production Car2x Projects Testing in Heterogeneous Tool Landscapes
Serial Bus Systems – K-Line K-Line: Flexible Solutions for a Classic Protocol 1/110 Case Study: Moore Industries 3/44
From Precise Monitoring to Data Manipulation for Generic Byte Protocols
Case Study: SsangYong Motor Company 3/45
Serial Bus Systems – MOST Data Communication in the Automobil Part 5 – MOST 1/114
Case Study: Autec 3/46
Development of distributed Controlling Complexity in the Vehicle Wiring System 2/0 Easy Access to Bus Analysis 3/48
Systems Model-based Wiring Harness Development
Eye On the Whole System 2/4
Why Consistent Implementation of the AUTOSAR System View is Worth it
These technical articles have been added since the last Pressbook edition.
Contents
Vehicle Diagnostics Automatic Validation of Diagnostic Services by Use 4/0 User-friendly Configuration of AUTOSAR ECUs with Specialized Software Tools 6/22
of a Diagnostic Integration and Validation Assistant at Opel
AUTOSAR Goes Multi-Core – the Safe Way 6/28
Automated Testing of Diagnostic Implementations Based
on the Example of the Opel Insignia. AUTOSAR-Compliant Development of an In-car Radio Product 6/32
Using MICROSAR for the European Market
Automated Data-driven Validation of the Diagnostic Implementation 4/8
High-Rate Task Scheduling within AUTOSAR 6/36
Automatic Diagnostic Validation is not Rocket Science 4/12
... Just a Matter of Consequent Exploitation of Existing Possibilities New Opportunities With AUTOSAR 6/40
The Standard Mix Does It 4/16
Functional Safety SilentBSW – Silent AUTOSAR Basic Software for Safety-Related ECUs 7/0
Part 1: Diagnostics with AUTOSAR
Coexistence of Safety-Related and Non-Safety-Related Software
The Standard Mix Does It 4/20 in one ECU by Protecting Memory Areas
Part 2: ODX in the AUTOSAR Development Process
Practical Implementation of Mixed-ASIL Systems 7/4
Diagnostic Tools for WWH-OBD 4/24 A Certified Operating System Simplifies the Development
Implementation of the New Requirements for OEMs and Suppliers of Safety-Related Software
Case Study: KTM 4/27 Seamless Implementation of ECU Software Based on ISO 26262 7/8
From Diagnostic Requirements to Communication 4/28 Is this what the Future Will Look Like? 7/14
Standardization is the Trend in the Development of Automotive Electronics Implementing Fault Tolerant System Architectures with AUTOSAR Basic Software
Diagnostics from a Distance 4/32 Safety and Performance with ASIL D AUTOSAR Basic Software 7/20
Interactive Diagnostics for Vehicles Worldwide
Has Functional Safety Ceased to Be a Topic of Interest? 7/24
Statement of Dr. Heling, Leader of the “Software ISO 26262” Working Group
ECU Calibration Data Recording for ADAS Development 5/0
within ZVEI
Scalable Recording of Sensor and ECU Data
All Puzzle Parts for OBD Documentation 5/6 Automotive Cyber Security Secure Communication for CAN FD 8/0
Integrated Process for Generating the Legally Required OBD Documentation
Cyber Security – Challenges and Practical Guidance 8/4
Faster and Without Errors
Success Factors for Security Engineering
Calibrating ECUs 5/10
Cyber Security for the Automotive Industry 8/12
Trends and Effects on Development Methods and Tools
Practical Experiences on the Application of Cyber Security
Analyze Large Quantities of Measurement Data Rationally and Flexibly 5/14
Risk-Oriented Automotive Cybersecurity 8/18
Verification of Driver Assistance Systems in the Vehicle and in the Laboratory 5/18 Industry Experiences and Case Study
Calibration Data Management: A Puzzle Game No More 5/22
E-Mobility E-Mobility Ready for the Mass Market? 9/0
Case Study: BMW 5/27 Trends, Progress and Experiences
Riding on the Razor’s Edge 5/28 Commercial Vehicles and Electromobility 9/4
Optimal Parameterization of an Engine Controller for Drag Racing Charging Ahead
Case Study: HOERBIGER 5/31 Inductive Charging 9/8
From Evaluation to Standardized E-Mobility
AUTOSAR AUTOSAR ECU Development Process Using DaVinci and MICROSAR 6/0
Inductive Charging Gives Trigger to Future of E-Mobility 9/12
from Vector
ISO/IEC-15118 Standardization of Wireless Power Transfer
Case Study: vSBC 6/7
Smart Testing of Smart Charging 9/16
AUTOSAR Methodology in Practice 6/8 Consistent Test Case Coverage for Electric Mobility
On-Board Diagnostics Meets AUTOSAR 6/12 Case Study: ZSW 9/21
Case Study: AUTOSAR 6/13 Smart Charging 9/22
A Key to Successful Electric Mobility
AUTOSAR in Heavy-Duty Vehicles 6/14
Integration of J1939 in AUTOSAR ECU Testing for Electric and Hybrid Vehicles 9/26
Intelligent Measuring the Dynamic Power Consumption
Case Study: PATAC 6/17
New Bus Interfaces for Electric/Hybrid Vehicle Development 9/30
AUTOSAR – Equipped for Everything? 6/18
Realtime Performance Enables Flexible Use in the EV/HEV Development Field
These technical articles have been added since the last Pressbook edition.
Contents
Open Networks – SAE J1939 Networking Heavy-Duty Vehicles Based on SAE J1939 10/0
From Parameter Group to Plug-and-Play Application
Quo Vadis SAE J1939 Standardization 10/6
Integration of J1939 Systems in Practice 10/12
CAN and J1939 Under Extreme Duty Conditions 10/16
Vehicle Electronics Guarantees Functionality in Cold, Ice and Snow
Current Trends in Network Development for Heavy-Duty Vehicles 10/22
Factors of Success in Electronic Development
Open Networks – ISOBUS Automatic Interoperability Tests for ISO11783 Systems 10/26
Universal Test Solution Assures Compatibility
Forging New Pathways in Testing ISOBUS Task Controllers 10/30
Simulations Replace Inflexible and Time-Intensive Test Methods
Better Test Quality by Automation 10/36
Automated HIL Test System Ensures ISOBUS Functionality
of Agricultural Machines
Development of a Cooperative Tractor-Implement Combination 10/42
Open Networks – CANopen Prototyping and Testing CANopen Systems 10/48
Reaching Goals Rapidly with Minimal Effort
Automatic Testing of CANopen Devices 10/52
Consulting Connectivity 11/0
Practical Experiences with Smart Systems and Services
Lean Requirements Engineering 11/6
Improving Engineering Efficiency with PLM/ALM 11/10
These technical articles have been added since the last Pressbook edition.
Vector – the Company
Information at a Glance
The Vector Portfolio
Vector Informatik is the leading manufacturer of software
Development of Distributed Systems Testing
tools and embedded components for the development of
Tools and services to support you in designing and developing Tools and services that provide a scalable and re-usable
electronic systems and their networking with many
networks and networked ECUs - especially for simulation, solution from pure SIL simulations to HIL testing with func-
different systems from CAN to Automotive Ethernet.
analysis and testing of network communication. tional acceptance tests.
Vector has been a partner of automotive manufacturers
Main product: PREEvision Main products: CANoe, CANalyzer, vTESTstudio, VT System,
and suppliers and related industries since 1988. Vector
Data Logger, VectorCAST
tools and services provide engineers with the decisive
advantage to make a challenging and highly complex Employees Subsidiaries
subject area as simple and manageable as possible. Vector > 2,000 24 locations in
employees work on electronic innovations for the automotive worldwide 12 countries Diagnostics ECU Calibration
industry every day. Worldwide customers in the automotive, Tools and services to describe, implement, validate and test Tools to access the ECU at run-time for acquisition and
commercial vehicles, aerospace, transportation, and the diagnostic functionalities that are required to run diag- modification of measurement data and parameters to
control technology industries rely on the solutions and nostic services on an ECU. optimize ECU algorithms.
products of the independent Vector Group for the develop- Main products: CANdelaStudio, Indigo, vFlash, DiVa Main products: CANape, VX1000, vCDM, vSignalyzer,
ment of technologies for future mobility. vADASdeveloper
Reliable Partner with Quality
Our goal is excellence in all areas! Vector processes are
Embedded Software and Systems Consulting
worldwide regularly assessed and certified, and they
Software components for the ECU communication and for Vector offers consulting for the optimization of your tech-
comply with current standards: Customers Associations
re-programming (flashing) via CAN, LIN, FlexRay, MOST nical product development, the associated business
> Quality Management - ISO 9001 > 7,500 participation in
and Ethernet, real-time operating systems, AUTOSAR processes and tools, as well as for the successful implemen-
> Automotive SPICE companies 15 committees
basic software, diagnostic software, project work and tation of change.
> Functional Safety - ISO 26262 in 72 countries
services. Our offer: consulting services, engineering services
Main products: MICROSAR, Flash Bootloader, VC ECU,
customer projects
large that their weight and multitude of connectors was prob- name (identifier) of the sending supermarket or home im-
lematic, not to mention the logistic challenges that arose during provement store chain. Each receiver decides whether or
manufacturing, maintenance, and further development. not he uses the received information.
The sender pairs information and address respectively
What is a “Bus“? identifier thus allowing the receiver to recognize the unit. In
A pioneering solution for all of these problems was the in- transmission technology we refer to this unit as a “frame”
troduction of the so-called bus. The word “bus” comes from because the addresses and information are framed by a
the Latin word “omnibus”, which simply means “for all”. The start identification and end identification, which mainly
many individual cables were thus replaced by a single cable serve to ensure error-free transmission between the sender
that is shared by all information of all electronic control and receiver. It’s also referred to as a message or packet.
units (ECUs) (Figure 2).
However, it was then necessary to find ways to organize The Protection of Data
the timely transmission of this multitude of information The most important tasks of a serial bus system include
over common wires. Different technologies arose, which we timely data transmission at fast enough rates for the par-
refer to as serial bus systems. ticular technical application and, above all, the protection
Before we delve into the specific characteristics of the indi- of data during transmission. The use of a serial bus system
vidual bus systems in the subsequent articles in this series, in the automobile depends in large part on the degree of
we will start by explaining the technical fundamentals of protection needed and the amount of data per unit of time
the serial bus systems that are used in modern motor vehi- that must be transmitted.
cles and then compare their underlying concepts. The protection of a serial bus system depends on how well
A common characteristic of all buses is that each connected the system prevents errors during data transmission and
ECU shares a single input and output and, unlike in networks, how well it detects remaining data corruption. The residual
information does not have to pass through the ECUs. Thus, error probability is one measure for this protection. This is
when one ECU sends information on a bus, all other ECUs the product of probability A that the data to be transmit-
receive the information at almost the same time. The con- ted are corrupted and probability B that corrupted data
Data Communication in the Automobile – Part 1: dition “almost” is necessary solely on account of the signal remain undetected. The lower the residual error probability,
transit time on copper, which is approximately 5 ns/m. the more the data transmission is protected.
Architecture, Tasks, and Advantages of Serial Bus Systems
There are many different causes of data corruption. The
Addresses Just Like the Post Office most powerful are sparks from ignition plugs and electric
For smooth information exchange, the data to be sent motors. Other galvanic, capacitive, or inductive interactions
History to participate safely in road traffic as in self-driving cars, must be clearly allocated to its senders and receivers. We and electromagnetic fields also play a role. Even reflections
The first vehicles powered by gasoline engines already also knows as autonomous. Vehicles are also starting to be call this addressing. A general distinction is made between at the end of the bus cable are an internal cause of data
had electrical components, such as ignition coils, contact connected with one another and with road infrastructure sender-selective and receiver-selective addressing. We are errors on a serial bus. The more effective a bus is at elimi-
breakers, and spark plugs. These were quickly followed by devices as well as with the Internet via WLAN. familiar with both of these types of addressing from our nating or preventing these causes, the better the data
other electrical devices such as headlights, brake lights, However, none of these functions would be possible in the mailbox. With sender-selective addressing, the sender de- transmission is protected.
direction signals, interior lights, and windshield wipers. The automobile without data exchange between electronic com- fines the desired receiver using a unique destination ad- A few important data protection measures are sufficient.
introduction of components for entertainment and infor- ponents. And it is exactly this need for data exchange that dress. This corresponds to a standard letter with a destina- These include shielding the transmission medium (cable or wire)
mation, such as radios and record players and more recent- has proven to be and still remains the real challenge. Initial- tion address and return address. and all electrical and electronic components. Alter natively
ly cassette and CD players, meant that automobiles soon ly, a dedicated cable was used for the transmission of each In contrast to this, receiver-selective addressing identifies the principle of differential signal transmission (Figure 3)
contained electronic components as well. Since the 1970s, separate information message (Figure 1). As the amount of the information to be sent and not the ECUs. For this
electronics came along that improved or enhanced the information grew, however, the cable harnesses became so reason we talk about identifiers here and not addresses.
functions of the vehicle itself or made driving easier. The We recognize deliveries like this in our mailboxes from the
Sample Point
next stage in the 1980s was directed at driving safety, in-
cluding ABS and airbags, and expansion of comfort fea- age
olt Wire 1
tures such as air conditioning, mirror dimming and adjust- V ΔVnormal
Wire 2
ing, power windows, and cruise control. Node A Node B Node C Node A Node B Node C
Growing competition brought about by increasing global-
ΔVimpaired
ization ensured more and more innovation. Automobile
manufacturers met this multifaceted challenge with elec- Disturbance symmetrical
on both wires
tronics. The development of electronic components grew so
Node E Node D Node E Node D Time
rapidly in the 1990s that it is beyond the scope of this article
to list all of the individual stages. Nowadays, the focus is on
Figure 1: Point-to-Point-Connections Figure 2: Bus Networking Figure 3: Differential transmission on a twisted pair
environmental friendliness and on the ability of automobiles
1/0 1/1
Data Communication in the Automobile – Part 1
achieves a high degree of transmission protection without Is Information Transmitted Fast Enough? Architecture of Serial Bus Systems (AUTomotive Open System ARchitecture, Figure 6), which
the need for real physical shielding. Shielding would be too A bus system is regarded as capable of transmission in Based on the reference model for data communication provide the necessary transparency on a system or func-
expensive and does not adequately meet the requirements real- time [1], or real-time capable, if it can guarantee suffi- specified by the ISO (International Standardization tion level. Cross-vendor communication standards such as
for flexibility and heat resistance. Using differential signal ciently fast transmission of all data that accumulates for Organization), the serial bus interface of an ECU in the the serial bus systems CAN  [2], LIN  [3], FlexRay  [4],
transmission, information is serially transmitted over un- an application. The essential factors for this are the num- automobile is generally distributed among two (communi- MOST [5], and Ethernet [6] ensure more transparency on
shielded twisted pair with the help of voltage levels that ber and size of messages, the available transmission speed cation) layers. The physical layer implements the physical the lower communication levels.
are exactly symmetrically opposed. If the voltage on one (also referred to as bandwidth), and the bus access method bus connection including the physical signal transmission. CAN (Controller Area Network) is used mainly in the drive
wire increases by X volts, the voltage on the other wire of the ECUs. For the latter, a distinction is made between Above that is the data link layer with its tasks including and chassis areas and in the operation of the vehicle. LIN
decreases by X volts. As a result, the electric fields in the controlled bus access and random bus access (Figure 4). addressing, framing, bus access, synchronization, and error (Local Interconnect Network) is used to control simple
cables are exactly opposed and the resulting magnetic With controlled bus access, the bus access right of an ECU detection and correction (Figure 5). comfort functions, such as the air conditioning, seats,
fields around the wires cancel each other almost completely. is already defined before its bus access. Such systems are The physical bus connection is made with help of a trans- mirrors, and windows. MOST (Media Oriented System
Such a system hardly emits any noise. The voltage difference called deterministic systems because it can be exactly de- ceiver. A communication controller takes over the tasks of Transport) has long served the infotainment area with
between the two wires represents the signal from which termined or calculated when a particular ECU transmits the data link layer. If all ECUs on the bus use the same type transmission of video and audio signals that require large
external noise is subtracted. which data. Deterministic behavior is an important precon- of transceivers and communication controllers, the basic bandwidths. Also Ethernet is increasingly being used for
Sufficient clearance between the data transmission and dition for achievement of real-time. Because the entire preconditions exist for smooth data exchange. this. Currently, Ethernet is mainly used for diagnostics in-
power supply cables and between electrical and electronic communication sequence runs according to schedule and During serial communication, the sender’s application de- cluding flashing. In the future, however, its main use will be
components is helpful. It is also essential to limit the data can hardly be influenced, bus systems with controlled bus livers the data block to be sent together with addresses or in the driver assistance area, including the park assist and
transmission speed as well as the number and steepness of access are characterized by a poor dynamic response. identifiers to the communication controller. Check and syn- autonomous driving sub-areas. Finally, FlexRay should en-
the data signal edges and to terminate the two bus ends Bus systems with uncontrolled bus access avoid this dis- chronization information as well as start and end identifi- able the most demanding communication in safety-critical
with the characteristic impedance of the transmission advantage. Each ECU has the right to transmit data at any cation are added, so that a frame results. The transceiver applications such as electronically controlled steering and
medium to prevent reflections. time. This results in a very fast bus access but also poses now sends the frame on the bus. braking. However, lawmakers along with the automakers
Nevertheless, transmission errors can never be fully elimi- the following risk: Depending on the density and length of Most buses in automobiles are in the form of a cable to are finding it difficult to push forward here, by trying to avoid
nated, which is why error detection measures are needed. the messages and the available bandwidth, there is a which the ECUs are connected via short spur lines. This is the risks in these areas that are highly critical to safety.
The checksum calculation method is most commonly used. greater or lesser acute risk of collision. This is not an ideal called a line topology or bus topology. On the receiver side, CAN was developed in the early 1980s by Robert Bosch
With this method, the sender uses a defined algorithm to basis for real-time. the transceiver passes the frame to the communication GmbH and became an international standard (ISO 11898)
calculate a checksum from the data to be transmitted and If all ECUs monitor the bus continuously and send informa- controller, which checks the information, and if data is re- in 1994. The founders of Vector played a central role in this
includes it at the end of the message. A receiver can com- tion only when the bus is available, the risk of collision is ceived correctly, forwards the data block to the application. development. LIN (ISO 17987), FlexRay (ISO 17458), and
pare this checksum with the one that it has calculated from significantly reduced, but not fully reduced. This risk is elimi- For some tasks such as bus management, that is, the con- MOST came from cross-vendor organizations, namely the
the received data. If the two checksums do not match, nated altogether by introducing priorities for information, certed putting to sleep and waking up of all ECUs, and the LIN Consortium, FlexRay Consortium, and MOST Cooperation.
there is an error. The more sophisticated the algorithm and which can be recognized on the CAN bus with help of the diagnosing and configuring of ECUs, the functions of the Vector [7] supports automobile manufacturers and sup pliers
the longer the checksum, the better the data error detec- identi fier. However, even these bus access methods cannot physical layer and the data link layers are not sufficient. in networking using CAN, LIN, FlexRay, MOST, and Ethernet
tion capability. A checksum must not be too long, however, guarantee timeliness (real-time). The reason is that, as a The higher layers of the ISO reference model for higher with a consistent set of design and development tools as
because every message in turn becomes longer and less result of prioritization, there is a risk that messages with communication protocols are then used in order to achieve well as with software components and basic software for
data can be transmitted on the bus. lower priority will be subject to long delays and no longer be the required communication functionality. AUTOSAR ECUs. Advice, consulting services and tools for
If an error is detected, the question arises as to how to cor- received in a timely manner. process management supplement the areas of application.
rect it. Errors can be corrected based on the checksum con- Cross-Vendor Bus Technologies A comprehensive training program that includes basic semi-
tained in a message. However, this requires longer check- Intensified competition is ensuring more and more safety nars for CAN, LIN, FlexRay, and Ethernet rounds out the services.
sums and, in particular, immense computing capacity in the and comfort functions in automobiles. As a result, there is Parts 2 to 5 of this series cover the details of the serial bus
receiving ECUs. This correction method is not used in auto- not only a continual increase in the number of electronic systems CAN, LIN, FlexRay, and MOST.
mobiles. Instead, the faulty message is discarded and a components in vehicles but also a significantly higher de-
new transmission is requested. gree of networking and a rapid rise in data volumes since Closing Remarks About the Term “Real-Time”
most new automobile functions rely on data exchange. The The term “real-time” is often used loosely or imprecisely,
Bus Node Bus Node challenge arising from this is to keep the increasing com- because it is not very easy to grasp. Because I had to use it
Application Application plexity under control to ensure the continued quality and at the outset, I would like to clarify a few facts about this
„Bus access rights „Bus access rights
are assigned Controlled Random are not assigned reliability of functions. For this purpose, the automobile subject. Whoever wants to know more can draw on other
before bus access“ Bus Access Bus Access before bus access“
Communication Communication industry has developed standards, such as “AUTOSAR” sources. [1]
Communication Communication Protocol Communication Part 9 of DIN 44300 (Information Processing), which has
Centralized Decentralized collisNioont-free Collision-free Controller Controller been replaced by DIN ISO/IEC 2382, defines real-time as
– Polling – Token Passing – Carrier Sense – CSMA with follows: ”Real-time refers to the operation of a computing
– Delegated – Time Division Multiple Access Collision Transceiver Physical Layer Definition Transceiver
Token Multiple Access (CSMA) Avoidance system on which data processing programs are always
(TDMA) (CSMA/CA)
Bus operable such that processing results are available within a
specified time span. The data may occur randomly or at
Figure 4: Controlled and random bus access Figure 5: Architecture of serial bus systems Figure 6: AUTomotive Open System ARchitecture
predefined times, depending on the application.”
1/2 1/3
For a real-time capable system, it is thus not enough to
deliver a measurement or calculation result with the cor-
rect value. Rather, this also has to occur within a specified
response time. If this is not the case, the system has failed.
According to the theory of real-time systems, the required
response time must be calculated for an application run-
ning on the system.
People often speak carelessly about “real-time” if a pro-
gram runs without a noticeable delay. However this defini-
tion is not very accurate.
It is wrong to use “real-time“ as a synonym for “very fast“,
because real-time systems even have to schedule no-load
operations in order to also meet real-time requirements
under high load.
A distinction is made between hard real-time and soft real-
time. The distinguishing criterion is the different conse-
quences of a violation of the real-time requirements.
> Hard real-time requirements: If the system exceeds the
required response time, it has failed. Real-time systems
must always supply the correct result within the required
response time, and the user of a hard real-time system
must be able to rely on this. (For example, engine
control: if the requirements are violated, the engine
sputters and even damage may occur.)
> Soft real-time requirements: Such systems typically
meet the required response time but not always. Thus,
for example, the required response time reaches only an
average or satisfies a different statistical criterion. The
time requirements are not absolutely strict, but rather
are viewed as guidelines. Exceeding the required
response time is not regarded as a failure. It can be
exceeded frequently as long as it still falls within a toler-
ance range. Or, the response time can far exceed the
required response time occasionally. (For example, a
video conference: When response time requirements are
violated, the image “jerks“ but work can continue.)
Literature References:
[1] de.wikipedia.org/wiki/Echtzeit
[2] de.wikipedia.org/wiki/Controller_Area_Network
[3] de.wikipedia.org/wiki/Local_Interconnect_Network
[4] de.wikipedia.org/wiki/FlexRay
[5] www.mostcooperation.com
[6] de.wikipedia.org/wiki/BroadR-Reach
[7] www.vector.com
Ernst Christmann, Physicist, Mathematician
is a Senior Technical Trainer in the area of software tools for
ECU testing and development and has worked for Vector
Informatik GmbH in Stuttgart since 2004.
1/4
and sunroofs where it is subject to bending that can cause Events Trigger the Transmission of Messages
wire breaks. Here the fault-tolerant CAN low-speed trans- If a newsworthy event happens in everyday life, it is com-
ceiver with a maximum data rate of 125 kbit/s is used. It municated in newscasts. In the world of serial buses, the
can also be operated using a single wire. Although this type term “event” is also used to describe an occurrence that
of CAN bus is rarely used. requires information to be transmitted. For fast communi-
The CAN interface consists of a CAN controller and a CAN cation of information, the ideal situation is for the underly-
transceiver (Figure 2). ing event to directly trigger transmission of the respective
The CAN controller handles the CAN protocol. The CAN data. This is referred to as event-driven transmission.
transceiver connects the CAN controller physically to both The alternative would be to transmit information accord-
of the CAN wires and measures or generates the voltage ing to a prescribed schedule or time pattern. But, if infor-
levels on these two wires. mation is now produced that requires transmission and it’s
not the ECU’s turn to send, the transmission must wait.
What Has to Go from Where to Where? To avoid this wait, CAN was developed as an event-driven
CAN uses the receiver-selective form of addressing. The bus system. Every CAN node is authorized to access the
identifier (ID) indicates the content of the transmitted CAN bus immediately after occurrence of an event and to
data and not the destination. A message can thus be re- send data that has been created. The only exception is if
ceived and evaluated by all ECUs on the bus (message another ECU is already transmitting data. Courtesy dic-
distribution). The application of a receiving ECU decides tates that another transmission is not to be interrupted.
whether it evaluates a message. It can even set an accep- The important thing here is that the other transmission does
tance filter in its CAN controller when starting, which hides not last too long. CAN limits the message length to a maxi-
unneeded CAN messages in the message stream based on mum of 130 bits (for 11 bit identifiers). With the usual data
their identifiers. CAN offers two sizes of identifiers: 11 bit transmission rate of 500 kbit/s in passenger cars, this leads
and 29 bit. The smaller identifier (standard format) is used to a transmission duration of approximately 0.25 milli-
in passenger cars. It provides 2048 different messages, seconds. The bus is available again after that. This is an
while the larger identifier offers 536 870 912 messages. The important precondition for data transmission that must be
Data Communication in the Automobile – Part 2: latter is mainly required in commercial vehicles for CAN- sufficiently fast for applications like drive and chassis.
based software protocols, such as SAE J1939, but is now However, there is still a risk of collisions, namely when mul-
Reliable Data Exchange with CAN
found in passenger cars as well. tiple ECUs want to start transmitting messages simulta-
Receiver-selective addressing offers the following advan- neously after the bus becomes available again after a
tages: transmission. This danger rises with increasing bus load. If
As presented in part 1 of our article series, the increasingly physical bus connection, data rates, and the voltage levels > Cost savings through shared use of sensors by all ECUs messages were to be destroyed as a result of a collision,
complex electronic systems in automobiles are calling for a on both CAN wires. on the bus. this would cause the bus load to increase and initiate a vi-
higher level of data exchange between the ECUs. In order CAN uses differential signal transmission, which reduces > Easy implementation of distributed functions cious cycle that would place the availability of sufficient data
to ensure this with sufficient reliability and speed, the CAN noise sensitivity and requires two communication wires > It allows different configurations without adaptation of transmission speed in doubt. To avoid this, the CSMA/CA
bus was developed. CAN stands for Controller Area Network. (CAN high and CAN low) that are terminated at both ends hardware or software (Carrier Sense Multiple Access / Collision Avoidance) bus
As the name implies, the CAN bus can link a larger area and with characteristic impedance R of 120 Ω. access method is used in the CAN network.
T
reach a length up to multiple kilometers. CAN high-speed is mainly used in drive and chassis applica-
The CAN bus was developed by Bosch [1] and became a tions. It is primarily implemented by the CAN high-speed Priorities Instead of Collisions
standard in 1993. It is currently available as ISO 11898 transceiver, which supports a maximum data rate of When an ECU wants to send, it must check whether the
(Figure 1). The standard is divided into multiple parts. The 1 Mbit/s. The CAN low-speed physical layer has been used bus is free (Carrier Sense – CS). If the bus is busy, the ECU
first part specifies the CAN protocol and covers all aspects mainly in the convenience area. It is placed in doors, seats, must wait. When the bus becomes available again, there is
of the data link layer (framing, addressing, bus access, a possibility that other ECUs have been waiting for it too.
Microcontroller
data integrity) and the physical signal coding as part of the Application software communicating In this case, all ECUs start sending messages (Multiple
with other ECUs via messages over
physical layer of the ISO 7498 reference model – the so- the bus Access – MA). To avoid the impending damage from this
CAN Controller
called OSI layer model (OSI: Open Systems Interconnec- ISO 7498 CAN CAN Standard Implementation Message completion, Controls bus collision (Collision Avoidance – CA or Collision Resolution –
2 LLC access, transmission and reception
tion). The CAN controller was developed for handling the DaLtaay eLrink MAC PrCotAoNcol ISO 11898-1 CoCntArNoller of messages, bit timing CR), a process now occurs that is referred to as bitwise
CAN protocol. 1 PLS CTraAnNsm Tissriaonn: Tsrcaensivlaetiron of bits arbitration.
Parts 2 and 3 of ISO 11898 describe two versions of the PLhaysyiecral PMMDAI PhysiCcaAlN Layer IISSOO 1111889988--23 TranCsAcNeiver iRsnaetmcoe pvplotelidtoa,n fg:o eVr owleltavaerdglsee dle tvoe lCs oanrteroller CECAUN CECAUN All ECUs with a transmission request simultaneously send
physical layer, namely CAN high-speed and CAN low-speed. the identifier of their respective CAN message to be trans-
The latter is also often called fault-tolerant CAN because it LMLACC LMoegdiciuaml L Ainckc eCsosn Ctroonltrol IISSOO 1111889988--12 CCAANN PHrigohto-Scopleed RT CAN_H mitted, bitwise from the most significant to least signifi-
PLS Physical Signalling Physical Layer
continues functioning if one of its two wires breaks, al- PMMDAI PMheydsiiucmal MDeepdeiunmda Anttt Ianctheerfmaecnet ISO 11898-3 CPhAyNs icLaolw L-aSypeered CAN_L RT cant bit.
though with diminished reliability. Parts 2 and 3 also cover A bit with significance 0 is dominant on the CAN bus. This
Figure 1: CAN Standard Figure 2: Structure of a CAN ECU
the physical layer of the ISO reference model, including the means if two ECUs simultaneously transmit different bit
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