Articles, Blog

Guaranteeing the real-time performance of in-vehicle networks

January 21, 2020


In the early nineteen nineties cars used
point to point wiring to connect the electronic control units (or ECUs) used for engine management,
transmission control, anti-lock braking and so on. The average
luxury car had 30 kilos of wiring harness, over one kilometer of copper wire and
more than 2,000 separate connections. This was extremely expensive to
manufacture, install and maintain. It was also
failure prone and unreliable. During the nineteen nineties the automotive industry began to use
Controller Area Network a multi-plex digital communications bus
used to connect ECUs. This approach dramatically
reduced the size weight and complexity of the wiring harness
for example with can-bus as it is commonly known, a
door system in a high-end car, typically requires four
wires compared to fifty plus with point to
point wiring. The information communicated over CAN is
in the form of signals. There are small pieces of information
such as dashboard switch positions, wheel speeds, oil and water temperature,
battery voltage and engine RPM. In a typical car there are over two and a half thousand
signals packed together in around 100 messages the are sent repeatedly over the CAN bus.
There a real time constraints or deadlines on the maximum time that
signals and hence the messages that contain them
are allowed to take to be transmitted over the network. A simple example is LED brake lights when the brake pedal is pressed this is
detected by an ECU in the instrument pack and a signal copied into a CAN message which is sent over the network. An ECU
in the rear of the vehicle receives the message decodes the signal and switches on the
LED brake lights. There is a short deadline on this, it
all happens in less than one twentieth of a second. Faster
than the time it takes an old-fashioned brake light to illuminate. The use of CAN lead to significant cost
savings and reliability improvements leading to its wholesale adoption by the
automotive industry. Today CAN is used in almost every new
car sold typical family cars have around 25 ECUs connected together by two or more
controller area networks. If a CAN message fails to meet its
deadline than the reliability and functionality
of the vehicles electronic systems can be compromised this leads to intermittent problems and
high warranty costs associated with no fault found
replacement and expensive electronic control units. The challenge
is to guarantee that all of the hundred or so different messages
sent over the network will meet their deadlines under all
possible conditions. Prior to research in this area by the
real time systems group at the University of York the automotive industry used an ad hoc
approach to assigning message priorities and relied on extensive testing to try
and determine if there would be any missed deadlines during operation.
This approach gave no guarantees it also only allowed a small fraction of
the available network bandwidth to be used before the system became unreliable due
to intermittent timing failures. In the mid 1990s researchers in the real time systems
group here at the University of York developed schedulability analysis
Controller Area Network this is a mathematical technique that
can be used to calculate the longest possible time that each message can take from being queued on one ECU to being broadcast over the network and so
received by all of the other ECUs. This analysis enables system designers
to determine, before they build their system, if all of the messages can be guaranteed
to always meet their deadlines during operation and hence to prove if the system will be
free from timing failures. Further research at York also showed how
to assign message identifiers which are used to prioritise transmission
of messages on CAN to make the best possible use of the
available network bandwidth without causing deadlines to be missed. As a consequence of this world class research we founded a startup company which along
with industrial partner Volvo Car Corporation transferred this technology to industry
in the form of the volcano communications concept. Since its first use on the Volvo s80 in 1998, Volcano has been used for CAN
communications in over five million Volvo cars. Volcano technology is also used by
Jaguar, Land Rover, Aston Martin, Mazda the Chinese automotive giant SAIC and by the world’s leading automotive
suppliers including both Robert Bosch and Visteon. The main advantages of
Volcano come from using the schedulability
analysis and priority assignment methods that were developed in the real time
systems group at York. This analysis enables system architects to configure in vehicle networks using
CAN and systematically check that all of the
messages can be guaranteed to meet their
deadlines at network loads of up to around 80 per cent. This compares very favorably with a
maximum of about 30 percent achieved using other approaches that are
still in use in industry today. The car manufacturers using Volcano have achieved significant improvements in both network efficiency and reliability. They’ve seen substantial
reductions in the time and effort required for testing and development and eliminated warranty costs due to
network timing issues. In a competitive marketplace, these
benefits to the car manufacturers have been passed on to us as
consumers in terms of less expensive cars with more functionality and much better
reliability. The future challenges in this area arise from the use of multiple networks
often of different types with signals and
messages transferred between them. Here the inflexibility of some legacy
applications gives rise to a number of interesting
issues which is still being researched today. A new CAN standard has also been
proposed allowing flexible high speed data rights
this brings a whole new set of research problems. The real time systems group at York
remain at the forefront of research into real-time communications and continue to produce world-class research in this area.

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5 Comments

  • Reply naresh korlapati April 2, 2017 at 8:31 pm

    very informative

  • Reply ricardo Lopez-Montes March 24, 2018 at 12:52 am

    got it,.

  • Reply Rooster Hunter April 15, 2019 at 7:39 am

    Not going to mention how this technology tracks you! CAN Bus allows creeps to spy on you. I'll be keeping my old school wiring harness…thank you very much!

  • Reply AMAN KANWAR June 18, 2019 at 8:41 pm

    Hey some other channel is using your video, please report the same,

    The link to the video is https://www.youtube.com/watch?v=Mpk1LLV5ZC8
    Channel Name is Manjunath Savadatti

  • Reply Osama Nasher August 7, 2019 at 3:00 am

    Dears,
    I like this vidio i get one question. How can extract data from ECM to monitor tge cidition of fuel, oil and air filters? Is there's tools ??

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