/**
  @page I2C_TwoBoards_ComPolling I2C Two Boards Communication Polling Example
  
  @verbatim
  ******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
  * @file    I2C/I2C_TwoBoards_ComPolling/readme.txt 
  * @author  MCD Application Team
  * @version V1.5.0
  * @date    14-April-2017
  * @brief   Description of the I2C 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 

How to handle I2C data buffer transmission/reception between two boards, 
in polling mode.

   _________________________                        _________________________
  |           ______________|     ___VDD____       |______________           |
  |          | I2C1         |     |        |       |          I2C1|          |
  |          |              |     R (4.7K) R       |              |          |
  |          |      SCL(PB6)|_____|________|_______|(PB6)SCL      |          |
  |          |              |              |       |              |          |
  |          |              |              |       |              |          |
  |          |              |              |       |              |          |
  |          |      SDA(PB7)|______________|_______|(PB7)SDA      |          |
  |          |              |                      |              |          |
  |          |______________|                      |______________|          |
  |      __                 |                      |             __          |
  |     |__|                |                      |            |__|         |
  |     USER             GND|______________________|GND         USER         |
  |                         |                      |                         |
  |_STM32F103RB_NUCLEO______|                      |_STM32F103RB_NUCLEO______|

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 I2C peripheral configuration is ensured by the HAL_I2C_Init() function.
This later is calling the HAL_I2C_MspInit()function which core is implementing
the configuration of the needed I2C resources according to the used hardware (CLOCK, 
GPIO). You may update this function to change I2C configuration.

The I2C communication is then initiated.
The project is split in two parts: the Master Board and the Slave Board
- Master Board
  The HAL_I2C_Master_Receive() and the HAL_I2C_Master_Transmit() functions 
  allow respectively the reception and the transmission of a predefined data buffer
  in Master mode.
- Slave Board
  The HAL_I2C_Slave_Receive() and the HAL_I2C_Slave_Transmit() functions 
  allow respectively the reception and the transmission of a predefined data buffer
  in Slave mode.
The user can choose between Master and Slave through "#define MASTER_BOARD"
in the "main.c" file:
- Uncomment "#define MASTER_BOARD" to select Master board.
- Comment "#define MASTER_BOARD" to select Slave board.

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 on the Master Board, I2C Master
starts the communication by sending aTxBuffer through HAL_I2C_Master_Transmit() to 
I2C Slave which receives aRxBuffer through HAL_I2C_Slave_Receive(). 
The second step starts when the user press the User push-button on the Master Board,
the I2C Slave sends aTxBuffer through HAL_I2C_Slave_Transmit()
to the I2C Master which receives aRxBuffer through HAL_I2C_Master_Receive().
The end of this two steps are monitored through the HAL_I2C_GetState() function
result.
Finally, aTxBuffer and aRxBuffer are compared through Buffercmp() in order to 
check buffers correctness.  

STM32F103RB-Nucleo's LED can be used to monitor the transfer status:
 - LED2 is ON when the transmission process is complete.
 - LED2 is OFF when the reception process is complete.
 - LED2 is slowly blinking (1 sec. period) in case of error in initialization or 
transmission/reception process

@note I2Cx instance used and associated resources can be updated in "main.h"
file depending hardware configuration used.

 @note Timeout is set to 10 Seconds which means that if no communication occurs 
       during 10 Seconds, a Timeout Error will be generated.


@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 

  - I2C/I2C_TwoBoards_ComPolling/Inc/stm32f1xx_hal_conf.h    HAL configuration file
  - I2C/I2C_TwoBoards_ComPolling/Inc/stm32f1xx_it.h          Interrupt handlers header file
  - I2C/I2C_TwoBoards_ComPolling/Inc/main.h                  Header for main.c module  
  - I2C/I2C_TwoBoards_ComPolling/Src/stm32f1xx_it.c          Interrupt handlers
  - I2C/I2C_TwoBoards_ComPolling/Src/main.c                  Main program
  - I2C/I2C_TwoBoards_ComPolling/Src/system_stm32f1xx.c      STM32F1xx system source file
  - I2C/I2C_TwoBoards_ComPolling/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 PB6 to Slave Board PB6
    - Connect Master board PB7 to Slave Board PB7
    - Connect Master board GND to Slave Board GND
    - Check that a pull-up resistor is connected on one I2C SDA pin
    - Check that a pull-up resistor is connected on one I2C SCL pin

@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>
 */
