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ETHERNET Powerlink Protocol Software

Overview of Functions

The EPL protocol software contains all the necessary functions for the implementation of controlled nodes or managing nodes in accordance with the EPL V2 specification. It does not contain a TCP/IP stack, which is required for running the SDO protocol via UDP, as this is usually provided by the operating system. Alternatively, an external TCP/IP stack (commercial or open source) can be used. The integration of an TCP/IP stack is simplified by the internal interfaces of the EPL stack.

Encapsulation of hard real-time tasks and hardware specific adaptation

The lower layers of the EPL software are specifically designed to guarantee fast response times of real-time events on the EPL bus. Therefore, the access and the handling of the Ehternet controller is encapsulated within a separate module, the lower layer driver (LLD). For an adaptation of the EPL software to a specific CPU or hardware platform, this module needs to be midified.

This abstraction between hardware-dependant routines and the higher layers of the EPL software makes it possible to provide a high degree of scalability and adaptability. A configuration tool delivered with the software allows optimum adaptation of the EPL functionality provided by the protocol stack to the given application and thus enables effective use of available resources which guarantees an extremely resource-efficient implementation.

Object dictionary and programming interface

The object dictionary is the interface between application and communication. Each object dictionary entry can be directly allocated a reference to a variable with application data. PDOs and SDOs access these application variables directly. Therefore, no modifications to an existing CANopen application are necessary to integrate and EPL protocol software.

User-specific call-back functions can be linked to every application object and enable an event-controlled notification of the application in the event of accesses to these objects. This mechanism allows a direct, application-specific reaction on modifications to the application data caused on the bus side. In addition, saving and recovery of configured data is also supported. The application is also able to build or modify parts of the Object Dictionary during operation.

Process (PDO) and Service Data Objects (SDO)

With PDOs, the EPL protocol software supports verification of the PDO version and of the PDO size. Depending on the configuration used, PDO mapping can be configured statically or dynamincally, according to the required reaction speed or available resources. Objects can be entered in several PDOs simultaneously.

With SDOs, the transfer types via UDP and via ASend (EPL frames) are supported. Both with read and write accesses, the SDO-service can be confirmed by the application with a delay. The application can thus check the data written by means of SDO for consistency before overwriting the target variables and if necessary abort the SDO transfer. This mechanism also enables data to first be acquired via another communication system (e.g. serial port) before they are transmitted.

Multi-channel support

The EPL-protocol software enables the implementation of several independent EPL interfaces in one device. Managing node or controlled node functionality can be configured independently, also with independent object dictionaries in each case. In this way, gateways can be developed that are connected to a higher order EPL network with one EPL channel as a controlled node and control an EPL sub-network as a managing node with the second EPL channel.

Operating system support

The EPL stack can be used with or without an operating system. The software has an internal scheduler which ensures the optimal allocation of the available process time resources to the various stack functions. By using an operating system, the EPL stack is executed as one task. Only basic operating system functions like semaphores and tasks are required. These functions are encapsulated by an abstraction layer (GOE-Generic Operating Environment) and can, due to this, be easily adapted to the operating system.

Reference platform

The provided "C" source code can be used on any target system. Besides the generic version, the delivered software package includes implementation samples, which work on Freescale Coldfire 523x based systems without the need of additional adaptation. Evaluation boards with wiring diagrams (reference schematics) are also available.

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