SIMHOL - a graphical simulator for the joint scheduling of messages and tasks in distributed embedded systems

Abstract In this paper a simulator to preview the timeliness of the transmission of messages and of the execution of tasks in a distributed system is presented. The simulator, called SIMHOL, builds on previous work by the authors in which a simple mechanism to dispatch tasks and messages was proposed for CAN-based distributed systems. The inputs to the simulator are the so-called data streams, which include the producer tasks, the correspondent messages and the tasks that use the transmitted data. Using the worst-case execution time and transmission time, the simulator is able to verify if deadlines are fulfilled in every node of the system and in the network. Besides discussing the simulator construction and operation, the paper presents some examples of distributed systems requirements and the results obtained by using the tool to analyze the respective timeliness. This is also used to illustrate the outputs of the simulator. One important issue also discussed is the easy way, due to the object oriented approach chosen, to extend the simulation to cover different networks and to use different scheduling techniques either at the task level or at the message level.

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