/**
  @page UART_TwoBoards_ComPolling UART TwoBoards Communication Polling example

  @verbatim
  ******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
  * @file    UART/UART_TwoBoards_ComPolling/readme.txt 
  * @author  MCD Application Team
  * @version V1.5.0
  * @date    14-April-2017
  * @brief   Description of the UART Two Boards Communication Polling 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 

UART transmission (transmit/receive) in Polling mode 
between two boards.

Board: STM32VL-Discovery (embeds a STM32F100xB device)
Tx Pin: PA.09
Rx Pin: PA.10
   _________________________                       _________________________ 
  |           ______________|                     |______________           |
  |          |USART         |                     |         USART|          |
  |          |              |                     |              |          |
  |          |           TX |_____________________| RX           |          |
  |          |              |                     |              |          |
  |          |              |                     |              |          |
  |          |              |                     |              |          |
  |          |           RX |_____________________| TX           |          |
  |          |              |                     |              |          |
  |          |______________|                     |______________|          |
  |                         |                     |                         |
  |                         |                     |                         |
  |_STM32_Board 1___________|                     |_STM32_Board 2___________|



Two identical boards are connected as shown on the picture above.
Board 1: transmitting then receiving board
Board 2: receiving then transmitting board
The user presses the User push-button on board 1.
Then, board 1 sends in polling mode a message to board 2 that sends it back to 
board 1 in polling mode as well.
Finally, board 1 and 2 compare the received message to that sent.
If the messages are the same, the test passes.


WARNING: as both boards do not behave the same way, "TRANSMITTER_BOARD" compilation
switch is defined in /Src/main.c and must be enabled
at compilation time before loading the executable in the board that first transmits
then receives.
The receiving then transmitting board needs to be loaded with an executable
software obtained with TRANSMITTER_BOARD disabled. 

STM32VL-Discovery board LEDs are used to monitor the transfer status:
- While board 1 is waiting for the user to press the User push-button, its LED3 is
  blinking rapidly (100 ms period).
- When the test passes, LED4 on both boards is turned on, otherwise the test has failed. 
- When the transmission or reception process are complete, LED3 is turned on.
- If there is an initialization or transfer error, LED3 is slowly blinking (1 sec. period).

At the beginning of the main program the HAL_Init() function is called to reset 
all the peripherals, initialize the Flash interface and the systick.
Then the SystemClock_Config() function is used to configure the system
clock (SYSCLK) to run at 24 MHz.


The UART is configured as follows:
    - BaudRate = 9600 baud  
    - Word Length = 8 bits (8 data bits, no parity bit)
    - One Stop Bit
    - No parity
    - Hardware flow control disabled (RTS and CTS signals)
    - Reception and transmission are enabled in the time

@note USARTx/UARTx instance used and associated resources can be updated in "main.h"
file depending hardware configuration used.

@note When the parity is enabled, the computed parity is inserted at the MSB
position of the transmitted data.

@note Care must be taken when using HAL_Delay(), this function provides accurate delay (in milliseconds)
      based on variable incremented in SysTick ISR. This implies that if HAL_Delay() is called from
      a peripheral ISR process, then the SysTick interrupt must have higher priority (numerically lower)
      than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
      To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.
      
@note The application need to ensure that the SysTick time base is always set to 1 millisecond
      to have correct HAL operation.

@par Directory contents 

  - UART/UART_TwoBoards_ComPolling/Inc/stm32f1xx_hal_conf.h    HAL configuration file
  - UART/UART_TwoBoards_ComPolling/Inc/stm32f1xx_it.h          interrupt handlers header file
  - UART/UART_TwoBoards_ComPolling/Inc/main.h                  Header for main.c module  
  - UART/UART_TwoBoards_ComPolling/Src/stm32f1xx_it.c          interrupt handlers
  - UART/UART_TwoBoards_ComPolling/Src/main.c                  Main program
  - UART/UART_TwoBoards_ComPolling/Src/stm32f1xx_hal_msp.c     HAL MSP module
  - UART/UART_TwoBoards_ComPolling/Src/system_stm32f1xx.c      STM32F1xx system source file


@par Hardware and Software environment 

  - This example runs on STM32F100xB devices.    
  - This example has been tested with two STM32VL-Discovery boards embedding
    a STM32F100xB device and can be easily tailored to any other supported device 
    and development board.

  - STM32VL-Discovery set-up
    - Connect a wire between 1st board PA.09 pin (Uart Tx) and 2nd board PA.10 pin (Uart Rx)
    - Connect a wire between 1st board PA.10 pin (Uart Rx) and 2nd board PA.09 pin (Uart Tx)
    - Connect 1st board GND to 2nd Board GND    

@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>
 */
