Analyzing SAE J1939 Messages Worst Case Response Time 2009-36-0242
The growth of embedded electronics, communication networks in vehicles, and distributed systems has lead to studies related to the scheduling and timing restrictions of these systems. A set of models and calculation methods related to the message latency time calculation were proposed since 90's based on the previous scheduling processors theory. Over the years we can see the development of whose theories and the application in different distributed systems, such as CAN Bus. This paper is focusing in embedded networks of the commercial vehicles, specifically, SAE J1939 protocol over CAN. The J1939 protocol is a SAE standard that defines a set of messages and parameters for commercial vehicles, as a recommendation practice, and also, allows the network designer to implement proprietary messages, which the data content is not defined by the standard. This paper shows, at first, an overview about the SAE J1939 protocol characteristics. The different CAN Bus timing calculation models, proposed in past years, and the differences between them are also presented as a knowledge base. Finally, this paper shows the usage of such models to analyze a given set of messages, providing the worst case response time predictions for each one, and, as a consequence, network timing behavior. The purpose of this paper is to propose a simple way to analyze the J1939 messages from a time restrictions point of view, in order to check the network behavior in the beginning of a project and when proprietary messages are inserted in existing network architecture.