这是ARM对AVR/C51升级的源程序xmodem，先通过TFTP将升级文件从PC下载到ARM，然后按照自己的握手方式，通过xmodem升级到AVR，已在产品中使用。-This is the source ARM upgrade of AVR/C51 xmodem, the first upgrade by TFTP to download files from PC to ARM, and then shook hands with their own way through xmodem u