ART-Linux for High-Frequency System Control

This paper presents the design and implementation of ART-Linux - a low-latency real-time extension of the Linux kernel for high-frequency system control. It is particularly tailored for the Intel x86 architecture, providing real-time (periodic) task execution system calls in user-space. ART-Linux provides simple yet strong system calls to allow periodic real-time programs to run in user-space with existing Linux device drivers, while providing users with standard developing, executing, debugging, and investigating environments. There is no need to add special device drivers. In order to achieve real-time functions in the Linux kernel, ART-Linux introduces the following techniques: 1) a mutual-exclusive execution mechanism realized by virtual processor numbers, 2) a transfer queue to avoid mutex-locked mutual-exclusive execution, and 3) a multi-level priority inversion function. A fine-grained implementation tuning of these techniques achieves very small jitters for specified periods (less than 20[mu s] in practice). Experimental results using a well-known humanoid robot called HRP-2 no.12 demonstrate that jitters of cycle times are retained in an acceptable range for humanoid control.