/**
  @page SPI_FullDuplex_ComIT SPI Full Duplex IT example
  
  @verbatim
  ******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
  * @file    SPI/SPI_FullDuplex_ComIT/readme.txt 
  * @author  MCD Application Team
  * @version V1.5.0
  * @date    14-April-2017
  * @brief   Description of the SPI Full Duplex IT example.
  ******************************************************************************
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
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  *      this list of conditions and the following disclaimer.
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  *      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
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  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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  ******************************************************************************
  @endverbatim

@par Example Description 

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

   _________________________                        _________________________
  |           ______________|                      |______________           |
  |          |SPI2          |                      |          SPI2|          |
  |          |              |                      |              |          |
  |          |     CLK(PB13)|______________________|(PB13)CLK     |          |
  |          |              |                      |              |          |
  |          |    MISO(PB14)|______________________|(PB14)MISO    |          |
  |          |              |                      |              |          |
  |          |    MOSI(PB15)|______________________|(PB15)MOSI    |          |
  |          |              |                      |              |          |
  |          |______________|                      |______________|          |
  |      __                 |                      |                         |
  |     |__|                |                      |                         |
  |     USER                |                      |                         |
  |                      GND|______________________|GND                      |
  |                         |                      |                         |
  |_STM32F1 Master _________|                      |_STM32F1 Slave __________|

HAL architecture allows user to easily change code to move to DMA or Polling 
mode. To see others communication modes please check following examples:
SPI\SPI_FullDuplex_ComDMA
SPI\SPI_FullDuplex_ComPolling

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 64 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 and NVIC). You may update this function to change SPI configuration.

The SPI communication is then initiated.
The HAL_SPI_TransmitReceive_IT() function allows the reception and the 
transmission of a predefined data buffer at the same time (Full Duplex Mode) 
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.

For this example the aTxBuffer is predefined and the aRxBuffer size is same as aTxBuffer.

In a first step after the user press the User push-button, SPI Master starts the 
communication by sending aTxBuffer and receiving aRxBuffer through 
HAL_SPI_TransmitReceive_IT(), at the same time SPI Slave transmits aTxBuffer 
and receives aRxBuffer through HAL_SPI_TransmitReceive_IT(). 
The callback functions (HAL_SPI_TxRxCpltCallback and HAL_SPI_ErrorCallbackand) update 
the variable wTransferState used in the main function to check the transfer status.
Finally, aRxBuffer and aTxBuffer are compared through Buffercmp() in order to 
check buffers correctness.  

STM32 board's LEDs can be used to monitor the transfer status:
 - LED2 toggles quicly on master board waiting user button to be pressed.
 - LED2 turns ON if transmission/reception is complete and OK.
 - LED2 toggle 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 

  - SPI/SPI_FullDuplex_ComIT/Inc/stm32f1xx_hal_conf.h    HAL configuration file
  - SPI/SPI_FullDuplex_ComIT/Inc/stm32f1xx_it.h          SPI interrupt handlers header file
  - SPI/SPI_FullDuplex_ComIT/Inc/main.h                  Header for main.c module  
  - SPI/SPI_FullDuplex_ComIT/Src/stm32f1xx_it.c          SPI interrupt handlers
  - SPI/SPI_FullDuplex_ComIT/Src/main.c                  Main program
  - SPI/SPI_FullDuplex_ComIT/Src/system_stm32f1xx.c      STM32F1xx system source file
  - SPI/SPI_FullDuplex_ComIT/Src/stm32f1xx_hal_msp.c     HAL MSP 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
    - Connect Master board PB13 to Slave Board PB13 
    - Connect Master board PB14 to Slave Board PB14
    - Connect Master board PB15 to Slave Board PB15
    - 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>
 */
 