/**
  @page AUDIO_Standalone USB Host AUDIO application
  
  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    USB_Host/AUDIO_Standalone/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the USB Host AUDIO application.
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; COPYRIGHT 2017 STMicroelectronics</center></h2>
  *
  * 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
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  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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  * 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 Application Description

This application shows how to use the USB host application based on the Audio OUT class on the STM32F4xx devices.

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. The user is provided with the SystemClock_Config()
function to configure the system clock (SYSCLK) to run at 100 MHz. The Full Speed (FS) USB module uses
internally a 48-MHz clock which is coming from a specific output PLL I2S.

When the application is started, the connected USB headset device is detected in AUDIO mode and gets 
initialized. The STM32 MCU behaves as a AUDIO Host, it enumerates the device and extracts VID, PID, 
manufacturer name, Serial no and product name information and displays it on the LCD screen. 

A menu is displayed and the user can select any operation from the menu using the Joystick buttons:
 - "Explore audio file" operation searches for all .Wav files in the uSD and displays it on the LCD screen.
 - "Start audio Player" operation starts playing the song from the uSD. The files are read using the 
   FatFs file system then USBH_AUDIO_ChangeOutBuffer() function is called while playing songs and the
   bytes are stored in a circular buffer. Sampling frequency, Channels number and File size (duration) 
   are detected. The audio.c file contains a set of APIs for Audio Out playback, for example when the 
   WAV file is playing, USBH_AUDIO_SetVolume() is called to change the volume setting. This application does not 
   support compressed WAV formats.
 - "Re-Enumerate" operation performs a new Enumeration of the device.

@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 needs to ensure that the SysTick time base is always set to 1 millisecond
      to have correct HAL operation.

For more details about the STM32Cube USB Host library, please refer to UM1720  
"STM32Cube USB Host library".


@par USB Library Configuration

It is possible to fine tune needed USB Host features by modifying defines values in USBH configuration
file usbh_conf.h available under the project includes directory, in a way to fit the application
requirements, such as:
  - Level of debug: USBH_DEBUG_LEVEL
                  0: No debug messages
                  1: Only User messages are shown
                  2: User and Error messages are shown
                  3: All messages and internal debug messages are shown
   By default debug messages are displayed on the debugger IO terminal; to redirect the Library
   messages on the LCD screen, lcd_log.c driver need to be added to the application sources.


@par Directory contents

  - USB_Host/AUDIO_Standalone/Src/main.c                  Main program
  - USB_Host/AUDIO_Standalone/Src/sd_diskio_dma.c         FatFS sd diskio driver implementation
  - USB_Host/AUDIO_Standalone/Src/system_stm32f4xx.c      STM32F4xx system clock configuration file
  - USB_Host/AUDIO_Standalone/Src/stm32f4xx_it.c          Interrupt handlers
  - USB_Host/AUDIO_Standalone/Src/menu.c                  MSC State Machine
  - USB_Host/AUDIO_Standalone/Src/usbh_conf.c             General low level driver configuration
  - USB_Host/AUDIO_Standalone/Src/explorer.c              Explore the uSD content
  - USB_Host/AUDIO_Standalone/Src/audio.c                 Audio Out (playback) interface API
  - USB_Host/AUDIO_Standalone/Inc/main.h                  Main program header file
  - USB_Host/AUDIO_Standalone/Inc/sd_diskio_dma.h         FatFS sd diskio driver header file
  - USB_Host/AUDIO_Standalone/Inc/stm32f4xx_it.h          Interrupt handlers header file
  - USB_Host/AUDIO_Standalone/Inc/lcd_log_conf.h          LCD log configuration file
  - USB_Host/AUDIO_Standalone/Inc/stm32f4xx_hal_conf.h    HAL configuration file
  - USB_Host/AUDIO_Standalone/Inc/usbh_conf.h             USB Host driver Configuration file
  - USB_Host/AUDIO_Standalone/Inc/ffconf.h                FAT file system module configuration file
 

@par Hardware and Software environment

  - This application runs on STM32F412xx devices.
    
  - This application has been tested with STMicroelectronics STM32F412G-Discovery Rev.C
    boards and can be easily tailored to any other supported device 
    and development board.

  - STM32F412G-Discovery Set-up
    - Connect the STM32F412G-Discovery board to the PC through 'USB micro A-Male 
      to A-Male' cable to the connector
    - Connect a uSD Card to the MSD connector (CN13)
    - Plug the USB headset for sound playback into the STM32F412G-Discovery board through
      'USB micro A-Male to A-Female' cable to the connector (CN3)

    - Please ensure that jumpers JP5 is fitted in position 1-2

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