/**
  @page USART_Communication_Rx_IT_Continuous USART Receiver example (IT Mode, Continuous reception)
  
  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    Examples_LL/USART/USART_Communication_Rx_IT_Continuous/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the USART_Communication_Rx_IT_Continuous example.
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2017 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

This example shows how to configure GPIO and USART peripheral for continuously receiving characters
from HyperTerminal (PC) in Asynchronous mode using Interrupt mode. Peripheral initialization is 
done using LL unitary services functions for optimization purpose (performance and size).

USART Peripheral is configured in asynchronous mode (115200 bauds, 8 data bit, 1 start bit, 1 stop bit, no parity).
No HW flow control is used.
GPIO associated to User push-button is linked with EXTI. 

Example execution:
After startup from reset and system configuration, LED2 is blinking quickly.
On press on User push-button, USART RX Not Empty interrupt is enabled.
When character is received on USART Rx line, a RXNE interrupt occurs. 
Received data is read from USART DR register and stored in user buffer.
A double buffer is available for received data, allowing continuous reception.
User could process data received in Buffer A, while buffer B is used for reception. 
When buffer B is full, it could be handled by user, while buffer A becomes active buffer for next reception, and so on.
Each time a reception buffer is full, user data process callback is called.
Data processing consists in echoing data buffer content on PC Com port, and making LED2 toggle.
In case of errors, LED2 is blinking.

Virtual Com port feature of STLINK could be used for UART communication between board and PC.

@par Keywords

Connectivity, USART, Asynchronous mode, RS-232, baud rate, Interrupt, HyperTerminal, Continuous Reception
VCP, 

@par Directory contents 

  - USART/USART_Communication_Rx_IT_Continuous/Inc/stm32f4xx_it.h          Interrupt handlers header file
  - USART/USART_Communication_Rx_IT_Continuous/Inc/main.h                  Header for main.c module
  - USART/USART_Communication_Rx_IT_Continuous/Inc/stm32_assert.h          Template file to include assert_failed function
  - USART/USART_Communication_Rx_IT_Continuous/Src/stm32f4xx_it.c          Interrupt handlers
  - USART/USART_Communication_Rx_IT_Continuous/Src/main.c                  Main program
  - USART/USART_Communication_Rx_IT_Continuous/Src/system_stm32f4xx.c      STM32F4xx system source file


@par Hardware and Software environment

  - This example runs on STM32F411xx devices.
    
  - This example has been tested with NUCLEO-F411RE board and can be
    easily tailored to any other supported device and development board.

  - NUCLEO-F411RE Set-up
    In order to select use of Virtual Com port feature of STLINK for connection between NUCLEO-F411RE and PC,
    User has to set USE_VCP_CONNECTION define to 1 in main.h file.
    If so, please ensure that USART communication between the target MCU and ST-LINK MCU is properly enabled 
    on HW board in order to support Virtual Com Port (Default HW SB configuration allows use of VCP)

    If VCP is not used (USE_VCP_CONNECTION define set to 0 in main.h file), Connect USART1 TX/RX 
    to respectively RX and TX pins of PC UART (could be done through a USB to UART adapter) :
    - Connect STM32 MCU board USART1 TX pin (GPIO PA.09 connected to pin 1 of CN5 connector)
      to PC COM port RX signal
    - Connect STM32 MCU board USART1 RX pin (GPIO PA.10 connected to pin 3 of CN9 connector)
      to PC COM port TX signal
    - Connect STM32 MCU board GND to PC COM port GND signal

  - Launch serial communication SW on PC (as HyperTerminal or TeraTerm) with proper configuration 
    (115200 bauds, 8 bits data, 1 stop bit, no parity, no HW flow control).
    Port should be selected according to USE_VCP_CONNECTION value.

  - Launch the program. Enter characters on PC communication SW side.

@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


 */
