Real-time design in a distributed control network application layer environment

The use of communication networks in time-critical control applications presents designers with special problems in the determination of response times for communicating distributed tasks. In the paper, using a ´structured analysis´ design approach, a real-time distributed application can be mapped to an application layer of a control network and guaranteed to meet its real-time requirements. The CAN (Controller Area Network) along with the CAN Application Layer (CAL) has been chosen as the experimental network. The ´CAN Messaging Service´ (CMS) elements of CAL are carefully selected to implement the ´distributed´ information flows and event flows produced by the ´structured design´ methodology. A real-time analysis approach for CALs CMS service elements is developed. Intelligent use of CALs inhibit times allow modelling of an event-driven system with properties inherent to a periodic system. Combining the worst-case computational, queuing and transmission delays, the response time for each distributed task can then be evaluated. This allows ´fine tuning´ of the distributed tasks until they can be guaranteed to meet their deadlines