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EtherCAT Protocol Implementation Issues on an Embedded Linux Platform

EtherCAT Protocol Implementation Issues on an Embedded Linux Platform. Sorin Potra LVD-Napomar Bd-ul Muncii, nr. 14, Cluj-Napoca, România Sorin.Potra@lvdnapomar.ro. Gheorghe Sebestyen Technical University of Cluj-Napoca G. Bariţiu, Nr. 26-28, Cluj-Napoca, România

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EtherCAT Protocol Implementation Issues on an Embedded Linux Platform

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  1. EtherCAT Protocol Implementation Issues on an Embedded Linux Platform Sorin Potra LVD-Napomar Bd-ul Muncii, nr. 14, Cluj-Napoca, România Sorin.Potra@lvdnapomar.ro Gheorghe Sebestyen Technical University of Cluj-Napoca G. Bariţiu, Nr. 26-28, Cluj-Napoca, România Gheorghe.Sebestyen@cs.utcluj.ro

  2. Project goal • To develop a driver for a Linux platform that implements the EtherCAT standard's specification for a master node

  3. 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

  4. EtherCAT - Ethernet Control Automation Technology • Industrial protocol - 2003 • Open specification • Features: • High speed message transmission • Deterministic master/slave medium access control policy • ‘on the fly’ slave operations execution • Bit level data addressing on slave devices

  5. Development Framework 5. 3. 4. • Hardware 1. • Software • Linux with RTAI extension • RTnet real-time Ethernet driver 2. 6.

  6. 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

  7. Control Application Communication interface D R I V E R Application level module EtherCAT module RT Network module Ethernet network 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

  8. 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

  9. Master driver – Test Application

  10. 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): • 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

  11. 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

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