定时中断实现任务切换,CPU 在空闲任务循环等待，定时中断将 CPU 周期性唤回，根据任务设计了不同的响应频度，满足条件的任务将获得CPU资源，CPU为不同任务“关照”完成后，再次返回空闲任务，如此周而复始，对于各个任务而言，好像各自拥有一个独立的CPU，各自独立运行。用这种思想构建的程序框架，最大的好处是任务很容易裁剪，系统能够做得很复杂。本程序就用了这种思想，使不同的灯用不同的频率闪烁。

-Timer interrupt for task switching, CPU cycles waiting for the idle task, timer interrupt the CPU periodically recall, according to mandate the design of the different frequency response, the task will be to meet the conditions of CPU resources, CPU for different tasks, " care"　is completed again return to the idle task, again and again, for all tasks, if each has a separate CPU, operate independently. Built with the thought that the procedural framework, the biggest advantage is that the task is very easy to cut, the system can do very complex. The program will use this idea to make a different light flashes with different frequencies.