/**
  **************************************************************************
  * @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, 150 mhz sysclk
  configed by crm_pll_config2 function. pa8 output crm_clkout_pll_div_4. 
  led2 fresh per 100 ms.
