/**
  **************************************************************************
  * @file     readme.txt
  * @brief    readme
  **************************************************************************
  */

  this demo is based on the ht32f49395_sk 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
