Research On Implementing Real-Time Publish/Subscribe Communication Protocol Based On CAN Bus

Communication is basic of real-time control system. Data is meaningful only when it is transferred reliably in a limited time. Distributed real-time application has unique communication requirements. Real-time applications must handle different kinds of data flow;many nodes intercommunication making data flow complex;and dynamic configuration changes occur as nodes leave and join the network. Strict timing requirements further complicate the entire design. Traditional Client/Server architectures route all communications through a central server. This make them ill-suited to handle real-time data distribution. Publish/Subscribe architectures, designed to distribute data to many nodes simultaneously and anonymously, have clear advantages for real-time application developers. In Publish/subscribe model, publisher and subscriber send or receive data anonymously and does not need to have detail information of networks, nor address of other nodes. Application can be publisher or subscriber or both of them. Publish/Subscribe work well in distributed application which handles complex data flow.CAN bus(CAN: Controller Area Network) is a kind of Field bus. Comparing to normal communication bus, the data communication of CAN bus has excellent characters of reliability, real-time and flexibility, and the strongpoint of Field bus. The CAN-bus is well suited to implement Publish/Subscribe communication model.The research of this thesis aim at the architectures of Publish/Subscribe and the technology of CAN bus of Field bus. The problem of routing, filtering, binding, reliability and efficiency must be solved, when implementing Publish/Subscribe model based on CAN bus. This thesis, desiged two function modules(Event Channel Handler and Event Channel Broker)based on trying to exploit CAN basic features as far as possible. The ECH provides an event channel interface to the application object and performs the filtering of messages based on their event tags. The ECB handles binding and configuration request. The system of implementing the procotol is composed of Supervisory PC, USBCAN card and the development platform of ARM7. This software is based on Real-Time Embedded Operating System of ucOS-II and Integrated Development Environment of ARM developer suite v1.2. The programming language is chosen as C.Through the test and analysis, the fuctions of ECH and ECB meet the need of the design, the Publish/Subscribe communication protocol based on CAN bus meets the need of real-time control system.