说明：  linux下串口通信的测试程序，是我初学串口编程的时候写的，附带的word是学习笔记，也是为初学者准备的，高手就不用看了
(linux serial port communication under the testing procedures, is my time learning to write serial programming, and incidental word learning notes, is also a preparation for beginners and experts do not need to read)