/**
  @page DFU_Standalone USB Device Firmware Upgrade (DFU) application
  
  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    USB_Device/DFU_Standalone/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the USB DFU application.
  ******************************************************************************
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  ******************************************************************************
  @endverbatim

@par Application Description 

This application is a part of the USB Device Library package using STM32Cube firmware. It describes how to 
use USB device application based on the Device Firmware Upgrade (DFU) on the STM32F207xx devices.

This is a typical application on how to use the STM32F207xG USB OTG Device peripheral to implement the DFU
capability for programming the embedded Flash memory of the STM32F207xG 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 120 MHz. The Full Speed (FS) USB module uses
internally a 48-MHz clock which is coming from the PLL.

The DFU transactions are based on Endpoint 0 (control endpoint) transfer. All requests and status 
control are sent/received through this endpoint.

The Internal Flash memory is split as follows:
 - DFU area located in [0x08000000 : USBD_DFU_APP_DEFAULT_ADD-1]: Only read access
 - Application area located in [USBD_DFU_APP_DEFAULT_ADD : Device's end address]: Read, Write, and Erase
   access

In this application, two operating modes are available:
 1. DFU operating mode: 
    This mode is entered after an MCU reset in case:
     - The DFU mode is forced by the user: the user presses the User button.
     - No valid code found in the application area: a code is considered valid if the MSB of the initial
       Main Stack Pointer (MSP) value located in the first address of the application area is equal to 
       0x2000
       
 2. Run-time application mode: 
    This is the normal run-time activities. A binary which toggles LEDs on the nucleo board is 
    provided in Binary directory.

@note After each device reset, hold down the User button on the nucleo board to enter the DFU mode.     

Traditionally, firmware is stored in Hex, S19 or Binary files, but these formats do not contain the 
necessary information to perform the upgrade operation, they contain only the actual data of the program
to be downloaded. However, the DFU operation requires more information, such as the product identifier, 
vendor identifier, Firmware version and the Alternate setting number (Target ID) of the target to be 
used, this information makes the upgrade targeted and more secure. To add this information, DFU file 
format is used. For more details refer to the "DfuSe File Format Specification" document (UM0391).

To generate a DFU image, download "DFUse Demonstration" tool and use DFU File Manager to convert a 
binary image into a DFU image. This tool is for download from www.st.com
To download a *.dfu image, use "DfuSe Demo" available within "DFUse Demonstration" install directory. 

Please refer to UM0412, DFuSe USB device firmware upgrade STMicroelectronics extension for more details
on the driver installation and PC host user interface.
    
@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 Device library, please refer to UM1734 
"STM32Cube USB Device library".
      
@par USB Library Configuration
      
It is possible to fine tune needed USB Device features by modifying defines values in USBD configuration
file “usbd_conf.h” available under the project includes directory, in a way to fit the application
requirements, such as:      
 - USBD_DFU_APP_DEFAULT_ADD, specifying the address from where user's application will be downloaded.

Device's end address is the end address of the Flash memory and it is dependent on the device in use.

@par Directory contents 

  - USB_Device/DFU_Standalone/Src/main.c                  Main program
  - USB_Device/DFU_Standalone/Src/system_stm32f2xx.c      STM32F2xx system clock configuration file
  - USB_Device/DFU_Standalone/Src/stm32f2xx_it.c          Interrupt handlers
  - USB_Device/DFU_Standalone/Src/usbd_conf.c             General low level driver configuration
  - USB_Device/DFU_Standalone/Src/usbd_desc.c             USB device descriptor
  - USB_Device/DFU_Standalone/Src/usbd_dfu_flash.c        Internal Flash memory management
  - USB_Device/DFU_Standalone/Inc/main.h                  Main program header file
  - USB_Device/DFU_Standalone/Inc/stm32f2xx_it.h          Interrupt handlers header file
  - USB_Device/DFU_Standalone/Inc/stm32f2xx_hal_conf.h    HAL configuration file
  - USB_Device/DFU_Standalone/Inc/usbd_conf.h             USB device driver Configuration file
  - USB_Device/DFU_Standalone/Inc/usbd_desc.h             USB device descriptor header file
  - USB_Device/DFU_Standalone/Inc/usbd_dfu_flash.h        Internal Flash memory management header file


@par Hardware and Software environment

  - This application runs on STM32F207xG devices.
    
  - This application has been tested with STMicroelectronics NUCLEO-207ZG Rev.B boards 
    and can be easily tailored to any other supported device and development board.

  - NUCLEO-207ZG Set-up
    - Connect the NUCLEO-207ZG board to the PC through 'USB micro A-Male to A-Male' cable
      to the connector (CN13)

  - Make sure that the jumper JP4 is closed

@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
 - To run the application, proceed as follows:
   - Install "DfuSe Demonstrator"
   - Install the DFU driver available in "DfuSe Demonstrator" installation directory  
   - Open "DfuSe Demo" and download the "STM32207_GPIO_0x8008000.dfu" provided in Binary
     directory.
   - To run the downloaded application, execute the command "leave the DFU mode" or simply reset the 
     board. 

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