/**
  **************************************************************************
  * @file     readme.txt 
  * @version  v2.0.5
  * @date     2022-05-20
  * @brief    readme
  **************************************************************************
  */

  this demo is based on the at-start board, in this demo, show how to build
  a device of usb virtual comport,when use this demo,please connect usart2 
  tx pin(pa2) and rx pin(pa3).
  for more detailed information, please refer to the application note document AN0097.

