/**
  **************************************************************************
  * @file     readme.txt
  * @version  v2.0.0
  * @date     2021-11-26
  * @brief    readme
  **************************************************************************
  */

  this demo is based on the at-start board, in this demo, swith sclk to
  pll based hick when hext clock failure occured. pa8 output crm_clkout_pll_div_4
  and led2 fresh per 200 ms.
