/**
  **************************************************************************
  * @file     readme.txt
  * @version  v2.0.3
  * @date     2022-02-11
  * @brief    readme
  **************************************************************************
  */

  this demo is based on the at-start board, in this demo, pa7 input external
  signal,debug view to see frequency and duty_cycle or use uasrt1 to see frequency
  and duty_cycle(pa9:usart1_tx). 
