Extending an open-source real-time operating system with hierarchical scheduling

Abstract

Hierarchical scheduling frameworks (HSFs) have been devised to support the integration of independently developed and analyzed subsystems. This paper presents an efficient, modular and extendible design for enhancing a real-time operating system with periodic tasks, two-level fixed-priority HSF based on the idling periodic and deferrable servers, and virtual timers. It relies on Relative Timed Event Queues (RELTEQ), a timed event management component targeted at embedded operating systems, which supports long event interarrival time, long lifetime of the event queue, no drift and low overhead. It minimizes the overhead in terms of processor and memory usage, limits the interference of inactive servers on system level, and minimizes the necessary modifications of the underlying operating system. The proposed design was implemented and evaluated within the µC/OS-II real-time operating system used by our industrial and academic partners