Research On Scheduling Algorithm And Resource Management In Real-time Operating System

Due to the rapid development of computer science and automatic control technology,real-time operating system has been widely applied to various fields, such as aviation,aerospace, navigation. Real-time operating system is concerned about outputting thecorrect results on time. Appropriate real time task processing must be completed within thegiven time limit. If the tasks’ deadline were not met, the system would appear irreparableerror. Many tasks in real-time systems are executed concurrently and resources can beshared, priority inversion phenomenon may occur in the system. Priority inversion problemmakes task cannot meet its deadline, serious priority unlimited reverses may cause thesystem to crash. Therefore, task scheduling and resource management are the mostimportant parts of the real time operating system.This paper chooses real-time kernel μC/OS-II to analyze because the code ofμC/OS-II is open. μC/OS-II supports only static priority scheduling. But with thedevelopment of real-time operating system, the real-time operating system requirementshave increased. So extend the μC/OS-II kernel to adapt the task priority schedulingrequirements’ changing in real-time systems by modifying the static scheduling algorithmin the scheduler to support the dynamic scheduling algorithm. In the real-time system,priority inversion causes unpredictable errors. This paper analyses the protocols to solvepriority inversion problem and verify several methods of restraining the priority inversionproblem in the μC/OS-II. This paper extends the priority inheritance method to priorityexchange by modifying the kernel code of signal. Analyze the reason of the deadlock andthe methods of solving deadlock. And do the experiment of task synchronization problemby using message mailbox to simulate task synchronization mechanism.Transplant the μC/OS-II kernel on pc computer. Use the BC45compiler environmentto do experiments. After many experiments, the extended μC/OS-II real-time kernelalgorithm can support the dynamic priority scheduling algorithm and still retains thecharacteristics of the preemptive kernel. For the management of resources, this paper controls the priority inversion on one level by using three methods. The three methods areclosing interrupt, priority ceiling and priority exchange.