Comparative analysis of a user space EtherCAT master application for hard real-time control

In this paper, we evaluate the real-time performance of an open source EtherCAT master developed by IgH Etherlab on Xenomai, running as a real-time co-kernel of standard Linux. The environment is implemented on top of two embedded platforms with different architectures, ARM and x86. First, Xenomai is ported on the target architecture in order to achieve real-time characteristics and to provide real-time mechanisms for inter-process communication used by the EtherCAT master. Although applications that run in the kernel space give better performance, programming is very difficult due to limited user-friendly functions. It is also fragile that a single mistake can easily crash the whole system. On the other hand, user space applications are uncomplicated and debugging is also simplified, with lesser risk of damaging hardware or reference memory. Thus, we developed a real-time application in the user space of Xenomai to actuate multi-axis servo drives focusing on the periodicity and execution time as performance measurements. The execution time of the EtherCAT master is evaluated and compared for each platform by calculating the difference between the timestamps during send and receipt of the EtherCAT frames. The experiment is performed both in short-term and long-term to test the consistency of each platform in carrying out hard real-time control applications.