A token-ring-like real-time response algorithm of Modbus/TCP message based on μC/OS-II

The Modbus/TCP protocol cannot guarantee the real-time capability. A token ring scheduling algorithm that featured by priority to provide the real-time response to the Modbus/TCP messages is designed. The average response delay on a μC/OS-II + ARM7 platform is 1.117 ms, which is better than most average response delay reported in current researches that aim at improving the real-time performance of Modbus/TCP, and, it reaches the level of Powerlink working in open mode. Finally, a weighted token ring scheduling algorithm and a weight-variable token ring scheduling algorithm are proposed. The two algorithms can meet the demand of customizable and changeable time delay in advanced application.