stm32通过串口来升级，从uboot启动，如果不需要升级代码，则直接跳转到应用代码，如果要升级则等待串口通过secureCRT　YMODE协议发送来得数据，注意（程序中由于ymodem协议没有发送文件大小，程序中是随便写了一个文件大小，对于我的app足够用），在app中随意按下按键，通过可以从应用程序跳转到uboot，然后发送1，通过ymodem协议发送.bin文件后，按下3则跳转应用程序(STM32 through the serial port to upgrade, starting from uboot, if you do not need to update the code, then jump directly into the application code, if you want to upgrade for the serial port by sending secureCRT YMODE get the data, note (procedures because the ymodem protocol did not send the file size, the program is not to write a file size for me app enough, press the button at random) in app, can jump to the uboot from the application, and then send the 1, through the ymodem protocol to send the.Bin file, press 3 jump applications)