/**
  @page I2C_TwoBoards_MasterTx_SlaveRx_DMA I2C example (DMA Mode)
  
  @verbatim
  ******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
  * @file    Examples_LL/I2C/I2C_TwoBoards_MasterTx_SlaveRx_DMA/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the I2C_TwoBoards_MasterTx_SlaveRx_DMA I2C example (DMA Mode).
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2016 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  @endverbatim

@par Example Description
  
How to transmit data bytes from an I2C master device using DMA mode 
to an I2C slave device using DMA mode. The peripheral is initialized 
with LL unitary service functions to optimize for performance and size.

This example guides you through the different configuration steps by mean of LL API
to configure GPIO, DMA and I2C peripherals using two STM32F103RB-Nucleo.

Boards: STM32F103RB-Nucleo (embeds a STM32F103RBT6 device)
SCL Pin: PB.6 (CN10, pin 17)
SDA Pin: PB.7 (CN7, pin 21)
A pull-up resistor must be connected on one I2C SDA pin
A pull-up resistor must be connected on one I2C SCL pin


   ______BOARD SLAVE_____    _____VDD _____     _____BOARD MASTER_____
  |        ______________|    |         |      |______________        |
  |       |I2C1          |    |         |      |          I2C1|       |
  |       |              |    R  (4.7K) R      |              |       |
  |       |          SCL |____|_________|______| SCL          |       |
  |       |              |              |      |              |       |
  |       |              |              |      |              |       |
  |       |          SDA |______________|______| SDA          |       |
  |       |______________|                     |______________|       |
  |         __           |                     |             __       |
  |        |__|          |                     |            |__|      |
  |        USER       GND|_____________________|GND         USER      |
  |___STM32F1xx_Nucleo___|                     |___STM32F1xx_Nucleo___|

The project is split in two parts the Master Board and the Slave Board
- Master Board
  I2C1 Peripheral is configured in Master mode with DMA (Clock 400Khz).
  And GPIO associated to User push-button is linked with EXTI. 
- Slave Board
  I2C1 Peripheral is configured in Slave mode with DMA (Clock 400Khz, Own address 7-bit enabled).

The user can choose between Master and Slave through "#define SLAVE_BOARD"
in the "main.h" file:
- Comment "#define SLAVE_BOARD" to select Master board.
- Uncomment "#define SLAVE_BOARD" to select Slave board.

A first program launch, BOARD SLAVE waiting Address Match code through Handle_I2C_Slave() routine.
LED2 blinks quickly on both BOARD to wait for user-button press. 

Example execution:
To perform this example, two steps are necessary to prevent a wrong start/stop detection due to the initialization of the opposite GPIO board.

So at first step, press the User push-button on BOARD SLAVE to activate Slave peripheral and then prepare acknowledge for Slave address reception.
At second step, press the User push-button on BOARD MASTER to activate Master peripheral and then to initiate a write request by Master.
This action will generate an I2C start condition with the Slave address and a write bit condition.
When address Slave match code is received on I2C1 of BOARD SLAVE, an ADDR event occurs.
Handle_I2C_Slave() routine is then checking the direction Read (mean write direction for Master).
This will allow Slave to enter in receiver mode and then acknowledge Master to send the bytes through DMA.
When acknowledge is received on I2C1 (Master), DMA transfer the data from flash memory buffer to I2C1 DR register (Master).
This will allow Master to transmit a byte to the Slave.
Each time a byte is received on I2C1 (Slave), DMA transfer the data from I2C1 DR register to RAM memory buffer (Slave).
And so each time the Slave acknowledge the byte received,
DMA transfer the next data from flash memory buffer to I2C1 DR register (Master) until Transfer completed.
Master generate a Stop condition when DMA transfer is achieved and TXE event occurs to be sure that all data have been acknowledge by Slave.

The STOP condition generate a STOP event and initiate the end of reception on Slave side.
Handle_I2C_Slave() routine is then clearing the STOP flag.

LED2 turn OFF on BOARD SLAVE when pressing the User push-button.

LED2 is On :
- Slave side if data are well received.
- Master side if transfer sequence is completed.

In case of errors, LED2 is blinking.


@par Directory contents 

  - I2C/I2C_TwoBoards_MasterTx_SlaveRx_DMA/Inc/stm32f1xx_it.h          Interrupt handlers header file
  - I2C/I2C_TwoBoards_MasterTx_SlaveRx_DMA/Inc/main.h                  Header for main.c module
  - I2C/I2C_TwoBoards_MasterTx_SlaveRx_DMA/Inc/stm32_assert.h          Template file to include assert_failed function
  - I2C/I2C_TwoBoards_MasterTx_SlaveRx_DMA/Src/stm32f1xx_it.c          Interrupt handlers
  - I2C/I2C_TwoBoards_MasterTx_SlaveRx_DMA/Src/main.c                  Main program
  - I2C/I2C_TwoBoards_MasterTx_SlaveRx_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
    - Connect GPIOs connected to Board Slave I2C1 SCL/SDA (PB.6 and PB.7)
    to respectively Board Master SCL and SDA pins of I2C1 (PB.6 and PB.7).
      - I2C1_SCL  PB.6 (CN10, pin 17) : connected to I2C1_SCL PB.6 (CN10, pin 17) 
      - I2C1_SDA  PB.7 (CN7, pin 21) : connected to I2C1_SDA PB.7 (CN7, pin 21)
    - Connect Master board GND to Slave Board GND
    - Check that a pull-up resistor (4.7K) is connected on one I2C SDA pin
    - Check that a pull-up resistor (4.7K) is connected on one I2C SCL pin

  - Launch the program. Press User push-button on Slave BOARD then on Master BOARD
      to initiate a write request by Master then Slave receive bytes.

@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 (The user can choose between Master 
   and Slave target through "#define SLAVE_BOARD" in the "main.h" file)
    o Comment "#define SLAVE_BOARD" and load the project in Master Board
    o Uncomment "#define SLAVE_BOARD" and load the project in Slave Board
 - Run the example


 */
