/**
  **************************************************************************
  * @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, debug to see counter
  added 4 each period.
  pin connection:
  - pa0    <--->    pa2
  - pa1    <--->    pa3  


