Vehicle Controller Area Network Response Time Analysis and Measurement Issues - to Reduce the Gap between Estimation and Measurement

摘要

Along with the efforts to cope with the increase of functions which require higher communication bandwidth in vehicle networks using CAN-FD and vehicle Ethernet protocols, we have to deal with the problems of both the increased busload and more stringent response time requirement issues based on the current CAN systems. The widely used CAN busload limit guideline in the early design stage of vehicle network development is primarily intended for further frame extensions. However, when we cannot avoid exceeding the current busload design limit, we need to analyze in more detail the maximum frame response times and message delays, and we need good estimation and measurement techniques. There exist two methods for estimating the response time at the design phase, a mathematical worst-case analysis that provides upper bounds, and a probability based distributed response time simulation. While both provide valuable information at design phase, we cannot easily measure message response times using the established bus tracing techniques because those bus traffic traces only contain the reception times of each message. Determining the response time requires knowing also the point in time this message is generated within the control unit, which is usually not possible. In this paper, we present an approach to approximate these intra-ECU message generation times in order to enable reasonable response time measurements. The approach uses a new frame-burst timing analysis that solely uses the standard bus trace information, in particular the reception times of frames. The improved method reduces the gap of estimation and measurement of timing behavior in a CAN network and enables analyzing the network timing efficiently at all phases of vehicle network developments.