/**
  **************************************************************************
  * @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, shows how to use
  the can loopback mode. every 1s transmit one message and the led4 blink, if
  the message can be received, led2 blink.
   set-up
  - can tx      --->   pb9
  - can rx      --->   pb8


