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

  this demo is based on the ht32f49395_sk board, in this demo, use hardware i2c1
  with two board communication based on dma mode. if the communication is
  successful, led3 will turn on, if the communication fails, led2 will keep flashing.
  change the macro definition MASTER_BOARD can switch among master-transmit/
  slave-receive master-receive/slave-transmit operation.

  attention:
    1. i2c bus must pull-up
    2. press the slave button first, then press the master button to start communication.

  pin used:
    1. scl --- pb6
    2. sda --- pb7
