Transcript EtherCAT Protocol Implementation Issues on an Embedded

EtherCAT Protocol
Implementation Issues on an
Embedded Linux Platform
Sorin Potra
LVD-Napomar
Bd-ul Muncii, nr. 14, Cluj-Napoca,
România
[email protected]
Gheorghe Sebestyen
Technical University of Cluj-Napoca
G. Bariţiu, Nr. 26-28, Cluj-Napoca,
România
[email protected]
Project goal
 To develop a driver for a Linux platform that
implements the EtherCAT standard's
specification for a master node
Industrial protocols – design issues
 Must offer:
 Real-time data delivery
 High reliability and dependability
 Priority based messaging
 Implementation issues:
 Developed on platforms with limited hardware and
software resource
 Requires guaranties for message delivery deadlines
 Driver’s features:
 Must have a highly predictable behavior

Must contain automatic fault recovery mechanisms
EtherCAT - Ethernet Control
Automation Technology
 Industrial protocol - 2003
 Open specification
 Features:
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High speed message transmission
Deterministic master/slave medium access
control policy
‘on the fly’ slave operations execution
Bit level data addressing on slave devices
Development Framework
 Hardware
5.
3.
4.
1.
 Software
2.
 Linux with RTAI extension 6.
 RTnet real-time Ethernet driver
Implementation problems:
Master driver - functionalities
 Initialize and configure the slave nodes
 Control of network traffic in a deterministic and
predictive manner
 Buffer and refresh the input and output process data
 Present a set of services to a higher level control
application that allow:
Changing a slave’s state
 Reading a slave’s state
 Start/Stop the refresh of the process data
 Write outputs
 Read inputs

Master driver - Structure
 Advantages of multi-module driver approach:
Offers a scalable and
flexible solution
 Allows the decomposition
of network functionality
 Suits EtherCAT standard
 Reduces complexity

Control Application
Communication interface
D
R
I
V
E
R
Application level module
EtherCAT module
RT Network module
Ethernet
network
Master driver – Implementation
 Implemented as a “real time task”
 Free of uncontrolled delays
Real time task
While
true
Receive telegrams
Wait for new cycle
Test pending responses
Do master state machine
Send cyclic telegrams
Master driver – Test Application
Experimental results
 Performance parameter = process data transmission
time
 Maximum delay of process image update is equal to
the periodicity of the real time task associated to the
master driver
 Process data transmission time (period):
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Must be as low as possible
Sufficiently high to allow the transmission of all
commands in a time frame
Depends on the size of the process image
 Test scenario:
 Single slave with process image of 32 digital signals
 Measured transmission time of IO image: 200us
Conclusions
 The developed master driver

Conforms to the EtherCAT standard
 Can
control complex systems with a
variable number of slave nodes
 Highly time-efficient implementation