CANopen is an application layer protocol based on the CAN bus. Porting it to the target platform generally requires the following steps:
1.Hardware Preparation
◦Ensure that the target microcontroller or microprocessor has a CAN controller. If there is no built-in CAN controller, an external CAN controller chip (such as SJA1000, etc.) may be required, and ensure that the CAN transceiver (such as PCA82C250, etc.) is correctly connected to the CAN controller and the CAN bus.
◦Design and produce the hardware circuit board, ensuring that the CAN bus’s electrical characteristics meet the requirements, including appropriate termination resistors (generally 120Ω), etc.
2.Development Environment Setup
◦Install the integrated development environment (IDE) corresponding to the target platform, such as Keil MDK, IAR Embedded Workbench, etc.
◦Prepare the compiler, debugger, and other tools for the target platform to ensure that code can be compiled, downloaded, and debugged.
3.CAN Driver Development
◦Write the CAN driver program according to the characteristics of the CAN controller of the target platform. This includes initializing the CAN controller (setting the operating mode, baud rate, filters, etc.), sending CAN data frame functions, and receiving CAN data frame functions.
◦For example, for a platform based on STM32, it is necessary to configure the relevant registers of the CAN controller, such as CAN_MCR (mode register), CAN_BTR (bit timing register), etc., to set the CAN operating mode and baud rate. The sending function needs to encapsulate the data into the CAN frame format and send it to the bus, while the receiving function needs to receive data from the CAN controller and process it.
4.CANopen Protocol Stack Porting
◦Select an appropriate CANopen protocol stack source code, which can be an open-source protocol stack (such as libcanopen, etc.) or a commercial protocol stack.
◦Read the documentation of the protocol stack to understand its architecture and usage.
◦Modify the protocol stack according to the characteristics of the target platform. This may include memory management, data type adaptation, interrupt handling, etc.
◦For example, the protocol stack may use standard C library functions for memory allocation (such as malloc and free), but on some resource-constrained microcontrollers, it may be necessary to implement a custom memory management mechanism. Additionally, the data types defined in the protocol stack may not match the default data types of the target platform’s compiler and need to be adjusted.
5.Object Dictionary Implementation
◦CANopen uses an object dictionary to describe various parameters and functions of the device. Create and configure the object dictionary based on the functional requirements of the device.
◦Each object in the object dictionary has a unique 16-bit index and an optional 8-bit sub-index. For example, the manufacturer’s ID of the device may be an object, with its index and sub-index clearly defined in the object dictionary.
◦Implement access functions for the object dictionary, including reading and writing the values of objects. These functions will be called by the CANopen protocol stack to communicate with other CANopen devices.
6.Device Function Implementation
◦Write the corresponding code based on the actual functions of the device and integrate it with the CANopen protocol stack.
◦For example, if it is a CANopen slave device, it is necessary to implement the state machine of the slave, handle various commands sent by the master (such as NMT commands), and update the device’s status and parameters according to the commands. At the same time, the device needs to send corresponding data (such as process data objects PDO) to the master based on its functions.
7.Debugging and Testing
◦Use a debugger to debug the ported code, checking for syntax errors, logical errors, etc.
◦Conduct CANopen communication tests, using CANopen master testing tools (such as CANopen Explorer, etc.) to communicate with the target device, checking whether the device can correctly respond to the master’s commands and whether data transmission is normal.
◦Perform functional tests to ensure that all functions of the device can operate normally and comply with the requirements of the CANopen protocol.
8.Optimization and Improvement
◦Based on the test results, optimize the code to improve its efficiency and stability.
◦Enhance the documentation of the device, including functional descriptions, CANopen configuration instructions, etc., to facilitate use and maintenance by other developers.
Porting the CANopen bus is a complex process that requires an in-depth understanding of the CAN bus, the CANopen protocol, and the target platform.