/**
  @page SPI_FullDuplex_ComPolling SPI Two Boards Communication example
  
  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    Examples_MIX/SPI/SPI_FullDuplex_ComPolling/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the SPI Full Duplex Polling example.
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; Copyright (c) 2017 STMicroelectronics.
  * All rights reserved.</center></h2>
  *
  * This software component is licensed by ST under BSD 3-Clause license,
  * the "License"; You may not use this file except in compliance with the
  * License. You may obtain a copy of the License at:
  *                        opensource.org/licenses/BSD-3-Clause
  *
  ******************************************************************************
  @endverbatim

@par Example Description 

Data buffer transmission/reception between two boards via SPI using Polling mode.

   _________________________                        _________________________
  |       ________CN10______|                      |_______CN10_________     |
  |      |SPI2              |                      |              SPI2  |    |
  |      |                  |                      |                    |    |
  |      |(pin30)  CLK(PB13)|______________________|(PB13)CLK  (pin30)  |    |
  |      |                  |                      |                    |    |
  |      |(pin28) MISO(PB14)|______________________|(PB14)MISO (pin28)  |    |
  |      |                  |                      |                    |    |
  |      |(pin26) MOSI(PB15)|______________________|(PB15)MOSI (pin26)  |    |
  |      |                  |                      |                    |    |
  |      |__________________|                      |____________________|    |
  |      __                 |                      |                         |
  |     |__|                |                      |                         |
  |     USER                |                      |                         |
  |                      GND|______________________|GND                      |
  |                         |                      |                         |
  |_STM32F1 Master _________|                      |_STM32F1 Slave __________|


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 72 MHz.

The SPI peripheral configuration is ensured by the HAL_SPI_Init() function.
This later is calling the HAL_SPI_MspInit()function which core is implementing
the configuration of the needed SPI resources according to the used hardware (CLOCK & 
GPIO). You may update this function to change SPI configuration.
The Full-Duplex SPI transfer (16bit) is done using LL Driver functions 
LL_SPI_TransmitData16 and LL_SPI_ReceiveData16.

Example execution:
First step, press the User push-button, this action initiates a Full-Duplex transfer 
between Master and Slave.
After end of transfer, aRxBuffer and aTxBuffer are compared through Buffercmp() in order to 
check buffers correctness.  

The user can choose between Master and Slave through "#define MASTER_BOARD"
in the "main.c" file.
If the Master board is used, the "#define MASTER_BOARD" must be uncommented.
If the Slave board is used the "#define MASTER_BOARD" must be commented.

STM32 board's LEDs can be used to monitor the transfer status:
 - LED2 toggles quickly on master board waiting User push-button to be pressed.
 - LED2 turns ON on both board if transmission/reception is complete and OK.
 - LED2 toggles slowly when there is a timeout or an error in transmission/reception process.   

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

@note You need to perform a reset on Master board, then perform it on Slave board,
      then press the User button on Master board to have the correct behaviour of this example.

@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 

  - Examples_MIX/SPI/SPI_FullDuplex_ComPolling/Inc/stm32f1xx_hal_conf.h    HAL configuration file
  - Examples_MIX/SPI/SPI_FullDuplex_ComPolling/Inc/stm32f1xx_it.h          SPI interrupt handlers header file
  - Examples_MIX/SPI/SPI_FullDuplex_ComPolling/Inc/main.h                  Header for main.c module  
  - Examples_MIX/SPI/SPI_FullDuplex_ComPolling/Src/stm32f1xx_it.c           SPI interrupt handlers
  - Examples_MIX/SPI/SPI_FullDuplex_ComPolling/Src/main.c                  Main program
  - Examples_MIX/SPI/SPI_FullDuplex_ComPolling/Src/system_STM32F1xx.c      STM32F1xx system source file
  - Examples_MIX/SPI/SPI_FullDuplex_ComPolling/Src/stm32f1xx_hal_msp.c     HAL MSP file    


@par Hardware and Software environment

  - This example runs on STM32F103xx devices.

  - Take care to cable connection between Master and Slave Board:
    Cable shall be smaller than 5 cm and rigid if possible.

  - This example has been tested with NUCLEO-F103RB board and can be
    easily tailored to any other supported device and development board.

  - NUCLEO-F103RB Set-up
    - Connect Master board PB13 to Slave Board PB13 (pin30 in CN10 connector)
    - Connect Master board PB14 to Slave Board PB14 (pin28 in CN10 connector)
    - Connect Master board PB15 to Slave Board PB15 (pin26 in CN10 connector)
    - Connect Master board GND  to Slave 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
    o Uncomment "#define MASTER_BOARD" and load the project in Master Board
    o Comment "#define MASTER_BOARD" and load the project in Slave Board
 - Run the example

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