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Implementation of CANopen

Implementation of CANopen

For the implementation of CANopen in embedded devices, protocol stacks are used, which are usually offered in form of company licenses. HMS offers under the IXXAT brand comprehensively tested CANopen protocol stack either as general C-code or already adapted to a large number of conventional microcontrollers The CANopen stack, available as "Slave" or "Master/Slave" , is proven in many applications. Terms "Slave" and "Master" refer to the different functionality with regard to network management, which is implemented in CANopen in the form of a logical Master/Slave relationship.

The CANopen stack equips a developer with the complete functionality required for communication, network management, general system services and device description. Implementation on the basis of a purchasable protocol stack therefore merely means connecting the application functionality to the protocol stack.

Structure of the CANopen protocol software


The IXXAT CANopen stack from HMS is structured in scalable, modular form in accordance with the various services of CANopen, such as Network Management (NMT), Process Data Objects (PDOs), Service Data Objects (SDOs), Emergency (EMCY), Synchronization (SYNC), SDO-Manager (SDM/SDR), Layer Setting Services (LSS) and Object Dictionary (OBD). All modules have access to the object dictionary, which represents the central instance of the software package as an interface between the communication interface and the data, parameters and functions of the application.

Access to the CAN controller (e.g. for transmitting and receiving messages) is carried out via a "Data Link Layer" interface, which is also integrated in a separate module (DLL-module). This allows fast and simple adaptation of the CANopen protocol software to different CAN controller implementations.
 
 
CANopen
Bus
CAN
controller
Data
Link
Layer
Communication
Interface
SDO
PDO
SYNC
MNS
NMM
ENCY
LED
FLY
SDM, SRD
LSS
Object
Dictionary
(OBD)
Application
(USR)

 
Software structure of the IXXAT CANopen stack

 

Simple configuration and optimized memory requirement


The functionality of the IXXAT CANopen stack can be easily adapted to the requirements of the application. For this, the developer just has to activate or deactivate functions/modules by means of "defines" in a central configuration file.

For the implementation of a slave with a reasonably useful functional scope on a 16-bit microcontroller, memory requirements of approx. 13k ROM and 1k RAM can be assumed as standard values. If the developer has fewer resources available, these values can be further reduced by means of specific modifications.

The important factors are a high degree of flexibility, comprehensive tests and assured
long-term maintenance and further development


HMS offers the IXXAT CANopen protocol software as cross-platform C-source code or already adapted to specific microcontrollers and CAN controllers. The developer therefore has all degrees of freedom to adapt and manage the software as necessary, like an own development.

Since the beginning of the CANopen standardisation activities, HMS has been actively involved in the CANopen organizations and is therefore definitely able to implement the latest version of the specifications at an early stage. HMS invests considerable amount of work in the continous advancement and maintenance of its CANopen stacks. By means of a software maintenance agreement, our customers can participate in this continual further development and benefit from the expert support of our CANopen specialists.

In order to supply customers with high quality products, HMS always tests its protocol stack against the current conformance test software of the CiA. This, together with the fact that the IXXAT software has been successfully used in the field for many years, guarantees our customers unproblematic, successful implementation of CANopen in their products and long-term maintenance.

Develop or buy?


Time and again there are developers who consider whether they should develop CANopen protocol software themselves, because the specifications are freely available without license costs and there are also several open source initiatives to date. Of course this is an interesting development challenge. However, from an economic point of view it is not at all worthwhile, as mature CANopen protocol software is offered nowadays by several manufacturers at very attractive prices.

For the development of a sufficiently tested and documented CANopen protocol stack a development time of at least 4 to 6 months is to be expected, even if the full functional scope of the specifications is not implemented. However, it remains to be seen whether an "initial implementation" is already a sufficiently optimized, fault-free product and whether the "subtleties" of the not exactly straightforward CANopen specification are correctly implemented. The possible setting up of free or open implementations does little to change this fact. Most of these approaches are only really of interest for training or other non-commercial environments.

If we assume that an in-house development of a CANopen protocol stack could be accomplished within 4 man months, at an hourly rate of EUR 60, the costs for such a development would be more than EUR 35.000. However this is a very optimistic estimation and a well tested and reliable solution supplied as source code off the shelf is available for a fraction of this price. Therefore an in-house development of a CANopen protocol stack is completely uninteresting from an economic point of view, including the time-to-market.

What does implementation of CANopen involve?


HMS supplies its IXXAT CANopen protocol stack with comprehensive documentation and sample programs. Project files are supplied with the sample programs that allow direct integration into the corresponding development environments of the compiler manufacturer. All sample programs can be run directly on a reference platform (evaluation board or IXXAT interface card).
 
The implementation is carried out as follows:
  • Adaptation to the hardware of the target platform (Timer, Interrupt system)
  • Creation of object dictionary entries
  • Adaptation of configuration file
  • Compiling and testing. For testing, the sample application can be transferred to the target platform. This can then also serve as the basis for the own application.

Early CANopen implementations on the target system can be set-up within a few days.
 
Alternatively, implementation can also be carried out by HMS. In this case, the requirements are specified together with the customer and then implemented by HMS. As the implementation is carried out by experienced engineers who are familiar with the software, this represents a low-cost, fast alternative to self-implementation.
 

Available CANopen software and tools


An overview of the available IXXAT protocol stacks can be found in the section "Protocol Stacks" or on the IXXAT website.
 
Useful tools for development and start-up, such as the canAnalyser, the CANopen Device Manager, or the CANopen ConfigurationStudio (basic) can be found in the section "Tools / Interfaces".