CprE 458/558: Real-Time Systems

CprE 458/558: Real-Time Systems (G. Manimaran)*CprE 458/558: Real-Time Systems Controller Area Network: Overview

(Updated by: Ki-sung Koo, CprE 458/558 TA)

CprE 458/558: Real-Time Systems (G. Manimaran)

CprE 458/558: Real-Time Systems (G. Manimaran)*Intra-vehicular communicationA typical vehicle has a large number of electronic control systems

The growth of automotive electronics is a result of:Customers wish for better comfort and better safety.Government requirements for improved emission controlReduced fuel consumption

Some of such control systemsEngine timingGearbox and carburetor throttle controlAnti-block systems (ABS)Acceleration skid control (ASC)


Intra-vehicular communicationAn example of intra-vehicular communication.CprE 458/558: Real-Time Systems (G. Manimaran)*


CprE 458/558: Real-Time Systems (G. Manimaran)*Intra-vehicular communicationThe complexity of these functions implemented by these electronic control systems necessitates an efficient communication between them.

In addition, a number of systems are being developed which will cover more than one device.

For exampleASC requires the interplay of the engine timing and carburetor control in order to reduce torque when drive wheel slippage occurs.

In the electronic gearbox control, the ease of gear changing can be improved by a brief adjustment to ignition timing


CprE 458/558: Real-Time Systems (G. Manimaran)*How do we connect these control devices?With conventional systems, data is exchanged by means of dedicated signal lines or wires.

But this is becoming increasingly difficult and expensive as control functions become ever more complex.

In the case of complex control systems in particular, the number of connections cannot be increased much further.

Solution: Use Fieldbus networks for connecting the control devices


CprE 458/558: Real-Time Systems (G. Manimaran)*Fieldbus Networks: basic motivationWhy use Fieldbus Networks? To avoid thisFigure 1 Traditional Wiring - two pairs of cables can substitute all typical connections.


Real-Time Communication ArchitectureThree different communication networks in real-time application.CprE 458/558: Real-Time Systems (G. Manimaran)*


CprE 458/558: Real-Time Systems (G. Manimaran)*Intra-vehicular communicationA schematic diagram of a current in-vehicle network

Smart Junction Box


CprE 458/558: Real-Time Systems (G. Manimaran)*Fieldbus NetworksFieldbuses are communication technologies and products used in vehicular, automation and process control industries.

1) Proprietary Fieldbuses (Closed Fileldbuses)Proprietary Fieldbuses are an intellectual property of a particular company or body.

2) Open FieldbusesFor a Fieldbus to be Open, it must satisfy the following criteria.a) The full Fieldbus Specification must be published and available at a reasonable price. b) Critical ASIC components must be available, also at a reasonable price. c) Well defined validation process, open to all of the Fieldbus users.


CprE 458/558: Real-Time Systems (G. Manimaran)*Fieldbus Advantages1) Reduces the complexity of the control system in terms of hardware outlay.

2) Resulting in the reduced complexity of the control system, project design engineering is made simpler, more efficient and conversely less expensive.

3) By selecting a recognized and well established system, this will make the Fieldbus equipment in you plant or plants interchangeable between suppliers.

4) The need to be concerned about connections, compatibility and other potential problems is eradicated.


CprE 458/558: Real-Time Systems (G. Manimaran)*What constitutes a Fieldbus?The specification of a Fieldbus should ideally cover all of the seven layers of the OSI model.


CprE 458/558: Real-Time Systems (G. Manimaran)*Fieldbus: OSI layer detailsPhysical Layer [1] What types of signals are present, levels, representation of 1's and 0's, what type of media connects, etc.

Link Layer [2] Techniques for establishing links between communicating parties.

Network Layer [3] Method of selecting the node of interest, method of routing data.

Transport Layer [4] Ensuring what was sent arrives at the receiver correcting any correctable problems.

Session Layer [5] Not applicable to Fieldbuses.

Presentation Layer [6] Not applicable to Fieldbuses.

Application Layer [7] Meaning of data.

The best way of covering layer 7 is to define standard profiles for standard devices.


CprE 458/558: Real-Time Systems (G. Manimaran)*What Fieldbus Networks are currently on the market? some of the Fieldbus technologies currently on the market AS-Interface (Europe)CAN (German, Bosch, we will discuss in detail)Interbus (German, Phoenix Contract)ModBus (America, Modicon)Profibus (German, Siemens)EtherNet (America, AB)Controlnet (America, AB)Etc.


CprE 458/558: Real-Time Systems (G. Manimaran)*Controller Area Network (CAN)Controller Area Network (CAN) is a fast serial bus that is designed to provide an efficient, Reliable andvery economical link between sensors and actuators.

CAN uses a twisted pair cable (dual-wire) to communicate at speeds up to 1Mbit/s (max) with up to 40 devices.

It originally developed to simplify the wiring in automobiles.

CAN (fieldbuse) are now used in machine and factory automation products as well.


CprE 458/558: Real-Time Systems (G. Manimaran)*CAN features1) Any node can access the bus when the bus is quiet.

2) Non-destructive bit-wise arbitration to allow 100% use of the bandwidth without loss of data (example)

3) Variable message priority based on 11-bit / 29 bit packet identifier

3) Peer-to-peer and multi-cast reception

4) Automatic error detection, signaling and retries

5) Data packets 8 bytes long

6) Asynchronous communication (Even Triggered)


CprE 458/558: Real-Time Systems (G. Manimaran)*CAN architectureCAN BusCS1CS2CS3CS40CAN Station 1CAN Station 40 (max).


CprE 458/558: Real-Time Systems (G. Manimaran)*Working of the CAN network: example


CprE 458/558: Real-Time Systems (G. Manimaran)*Tradeoff: CAN bus versus point-to-point connectionsBy introducing one single bus as the only means of communication as opposed to the point-to-point network, we traded off the channel access simplicity for the circuit simplicity

Since two devices might want to transmit simultaneously, we need to have a MAC protocol to handle the situation.

CAN manages MAC issues by using a unique identifier for each of the outgoing messages

Identifier of a message represents its priority.


CprE 458/558: Real-Time Systems (G. Manimaran)*CAN: message formatSupports only 11 bit identifier


CprE 458/558: Real-Time Systems (G. Manimaran)*Extended CAN message formatSupports 29 bit identifier


CprE 458/558: Real-Time Systems (G. Manimaran)*Physical CAN connection*ECU (Electrical Control Unit)


CprE 458/558: Real-Time Systems (G. Manimaran)*Implicit collision handling in the CAN busIf two messages are simultaneously sent over the CAN bus, the bus takes the logical AND of all them

Hence, the messages identifiers with the lowest binary number gets the highest priority

Every device listens on the channel and backs off when it notices a mismatch between the buss bit and its identifiers bit.


CprE 458/558: Real-Time Systems (G. Manimaran)*Implicit collision handling in the CAN bus: exampleNode Bs message-ID0000000000011111110100Node As message-IDBUS00011Node B notices a mismatch in bit # 3 on the bus.Therefore, it stops transmitting thereafterUnlike the MAC protocols we learnt, in CAN a collision does not result in wastage of bandwidth.Hence, CAN achieves 100% bandwidth utilization


CprE 458/558: Real-Time Systems (G. Manimaran)*Other applications of CAN 1) Concrete State Monitor & Control Ssytem


CprE 458/558: Real-Time Systems (G. Manimaran)*Other applications of CAN 2 ) MRI Cooling System


CprE 458/558: Real-Time Systems (G. Manimaran)*Other applications of CAN 3) Tram Energy Recycle System


CprE 458/558: Real-Time Systems (G. Manimaran)*Referenceshttp://www.fieldbus.com.au/techinfo.htm#Top

http://www.esd-electronics.com/german/PDF-file/CAN/Englisch/intro-e.pdf

http://www.eng.man.ac.uk/mech/merg/FieldbusTeam/Fieldbus%20Introduction.htm#_Toc487265349

In-Vehicle Network Architecture for the Next-Generation Vehicles Syed Masud Mahmud, Sheran Alles

http://www.can-cia.de/

http://www.icpdas.com/products/Remote_IO/can_bus/application.htm


CprE 458/558: Real-Time Systems

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