Design and application of a real-time industrial Ethernet protocol under Linux using RTAI

Nowadays, Ethernet networks have been extended down into the field of automation control from the upper planning and scheduling level, which caused the generation of a new form of communication using real-time industrial Ethernet fieldbus. This paper presents a feasible Ethernet-based real-time feildbus scenario for industrial automation control systems. It endeavours to gain high performance in general synchronisation real-time control systems with common hardware and software resources. For this purpose, a master-slave pattern is adopted in constructing the communication protocol. The slave nodes are developed based on universal FPGA and ARM chips, and the first slave node is in charge of precise cyclic timing and synchronisation among all slave nodes with time resolution of 20 nanoseconds. The master protocol stack is developed under Linux using Real Time Application Interface (RTAI), which not only provides application interface for user programs but also is responsible for exchanging process data with slave nodes in real time. A case study of merging this fieldbus into EMC2 to control a three-axis milling machine is also discussed and implemented. The experiment results show that this industrial Ethernet fieldbus platform completely meets the demand of open industrial automation control application.