Research On Key Technologies Of Real-Time System Task Scheduling

With widely application of real-time system in various fields, task scheduling technologies play an increasingly critical role in real-time systems. For the characters of multitask, multiprocessor and complex precedence constraints in real-time systems, this thesis, based on the analysis of traditional tasks scheduling theories, mainly focus on the study of the new theories and new methods of contemporary tasks scheduling technologies, especially on the different environments and conditions, schedulability analytical methods of the task systems and task scheduling algorithms are studied.The study in this thesis focus on the following areas:Because the rate monotonic analysis technology is lack of considerations for multiprocessor environment and precedence constraints relations between multitask, a tasks modeling and testing method based on Preemptive Time Petri Net is proposed. With the concept of state space enumeration and suspensive transitions, modeling and testing are performed for the tasks with precedence constraints in the multiprocessor environment. Simulating by examples shows that the new method can rapidly perform quantitative analysis for real-time task set with complex attributes on condition of multiprocessor and preemption.To solve the problem of schedulability tests of the periodic tasks, a tasks schedulability analysis method based on the cumulate time-demand analysis is proposed. The computation of additional response time caused by the task release jitter is added into the analysis of task busy interval. The accuracy of the periodic tasks schedulability test is enhanced and the problem of lacking of general schedulability analytical methods is solved.To avoid non-controlled priority inversion in the process of priority-driven tasks scheduling, a novel preventive method based on the preemption threshold theory is proposed. The problem of priority inversion and priority inheritance protocols as well as priority ceiling protocols are redefined under the preemption threshold, the task preemption is reduced and the priority inversion phenomenon...