DFU (Device Firmware Upgrade) is the standard method to upload paparazzi code to a stm32fx MCU via usb.
The native dfu bootloader is already embedded in the ROM of the MCU. The MCU will not go automatically in dfu mode, so either Luftboot is needed or it is done on hardware side (e.g. stm32f4-discovery).
Entering dfu mode
With extra bootloader
With native dfu bootloader
This can be used on the stm32f4-discovery board e.g.
Provide the board with power and connect the usb cable for dfu upload.
Connect BOOT0 pin with 3V pin(BOOT1 with GND ?), press reset button , disconnect BOOT0 and 3V.
This will list all devices in dfu-mode.
Flash_Mode=DFU must be set
<configure name="FLASH_MODE" value="DFU"/>
dfu-util is needed and must be installed
sudo apt-get install dfu-util
More information about dfu-util can be found at their Homepage http://dfu-util.gnumonks.org
Paparazzi Center acesses the usb port via "stm32_mem.py", just copy the required paparazzi udev rules into your system.