说明：  初次接触实时多任务操作系统的人，往往对实时程序的运行机制感到很困惑：任务在什么时候投入运行？操作系统以什么机制决定目前应该运行哪一个任务？本任务什么时候放弃了对CPU的控制？为了解答以上问题，我们从分析一个很简单的实时调度程序入手，来说明一下多任务程序的运行过程
(Initial contact with real-time multitasking operating system, often real-time operating system program was very confusing: When does the task into operation? What mechanisms determine the current operating system to which a task should run? The task of the CPU when to give up control? To answer these questions, we analyze a very simple real-time scheduler to start, to illustrate the operation of the process of multi-task program)