说明：  从STM官方例程中提取的Ymodem协议的C实现，亲测可用，可以与Windows超级终端互传文件。可以应用于32位或8位单片机，很实用的东东。
(From the STM official routine extracted from the Ymodem protocol C implementation, pro test available, you can share files with the Windows super terminal. Can be applied to 32 bit or 8 bit microcontroller, very practical dongdong.)