A Real-Time Scheduler Design for a Class of Embedded Systems

We consider here the design aspect of a real-time scheduler for a class of embedded systems. For this purpose, we design a feedback controller for a reservation-based CPU scheduler for soft real-time systems. The execution time of soft real-time systems, such as multimedia systems, portable MP3 players, personal digital assistants, cellular phones, and embedded Web servers is highly variable. Hence, it is crucial to assign an adequate amount of CPU resources for the running tasks to guarantee the quality of service. On the other hand, it is also important not to allocate the large amount of resources to avoid waste. The purpose of this paper is to attain the aforementioned crucial objectives for a class of embedded systems under real-time computing constraints. Specifically, we provide an analytical model for a real-time scheduler in terms of a switched system with time-varying uncertainty. Moreover, by using Lyapunov stability in a linear matrix inequalities (LMIs) framework, we design a state feedback controller that stabilizes the switched system. This, in fact, achieves the regulation of scheduling errors caused by time-varying uncertainty to a desired level. We extend an LMI-framework-based control scheme to a relatively new control application domain, i.e., a soft realtime scheduling domain. We provide performance analysis under scheduler simulation environments and implement a feedback bandwidth server scheduler under a real-time kernel simulator. In the simulation studies, the advantages of the controller design scheme are clearly highlighted in comparison with some conventional existing open-loop systems.