/**
  @page USART_Communication_TxRx_DMA USART Transmitter/Receiver example (DMA mode)
  
  @verbatim
  ******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
  * @file    Examples_LL/USART/USART_Communication_TxRx_DMA/readme.txt 
  * @author  MCD Application Team
  * @version V1.0.0
  * @date    14-April-2017
  * @brief   Description of the USART_Communication_TxRx_DMA example.
  ******************************************************************************
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *   1. Redistributions of source code must retain the above copyright notice,
  *      this list of conditions and the following disclaimer.
  *   2. Redistributions in binary form must reproduce the above copyright notice,
  *      this list of conditions and the following disclaimer in the documentation
  *      and/or other materials provided with the distribution.
  *   3. Neither the name of STMicroelectronics nor the names of its contributors
  *      may be used to endorse or promote products derived from this software
  *      without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  ******************************************************************************
  @endverbatim

@par Example Description

This example shows how to configure GPIO and USART peripheral
to send characters asynchronously to/from an HyperTerminal (PC) in
DMA mode. This example is based on STM32F1xx USART LL API. Peripheral
initialization is done using LL unitary services functions for optimization
purpose (performance and size).

USART Peripheral is configured in asynchronous mode (115200 bauds, 8 data bit, 1 start bit, 1 stop bit, no parity).
No HW flow control is used.
GPIO associated to User push-button is linked with EXTI. 
Virtual Com port feature of STLINK is used for UART communication between board and PC.

Example execution:
After startup from reset and system configuration, LED2 is blinking quickly and wait User push-button action.
USART and DMA are configured.
On press on push button , TX DMA transfer to PC is initiated. 
RX DMA transfer is also ready to retrieve characters from PC ("END" string is expected to be entered by user on PC side (HyperTerminal).
In case of both transfers successfully completed, LED2 is turned on.
In case of errors, LED2 is blinking (1sec period).

@par Directory contents 

  - USART/USART_Communication_TxRx_DMA/Inc/stm32f1xx_it.h          Interrupt handlers header file
  - USART/USART_Communication_TxRx_DMA/Inc/main.h                  Header for main.c module
  - USART/USART_Communication_TxRx_DMA/Inc/stm32_assert.h          Template file to include assert_failed function
  - USART/USART_Communication_TxRx_DMA/Src/stm32f1xx_it.c          Interrupt handlers
  - USART/USART_Communication_TxRx_DMA/Src/main.c                  Main program
  - USART/USART_Communication_TxRx_DMA/Src/system_stm32f1xx.c      STM32F1xx system source file

@par Hardware and Software environment

  - This example runs on STM32F103xB devices.

  - This example has been tested with STM32F103RB-Nucleo board and can be
    easily tailored to any other supported device and development board.

  - STM32F103RB-Nucleo Set-up
    In order use of Virtual Com port feature of STLINK for connection between STM32F103RB-Nucleo and PC,
    please ensure that USART communication between the target MCU and ST-LINK MCU is properly enabled 
    on HW board in order to support Virtual Com Port (Default HW SB configuration allows use of VCP)

  - Launch serial communication SW on PC (as HyperTerminal or TeraTerm) with proper configuration 
    (115200 bauds, 8 bits data, 1 stop bit, no parity, no HW flow control). 

  - Launch the program. Press on User push button on board to initiate data transfer.

@par How to use it ? 

In order to make the program work, you must do the following :
 - Open your preferred toolchain
 - Rebuild all files and load your image into target memory
 - Run the example

 * <h3><center>&copy; COPYRIGHT STMicroelectronics</center></h3>
 */
