UF2 Bootloader Update

The UF2 Bootloader

The UF2 bootloader can be used to upload and deploy new firmware updates on to the Falcon 1, 2 and 3 flight controllers much more easily than before. The UF2 bootloader is shipped with all current Falcon boards. The advantage of the UF2 bootloader over the standard bootloader is that no additional application is required to upload new firmware.

After double tapping the Falcon’s reset button, the flight controller appears as an additional drive (Mass Storage Device), like a memory stick. Firmware uploads are performed by simply dragging and dropping a UF2 file containing the new firmware on to the drive.

Installing The UF2 Bootloader

It is possible to upgrade Falcon boards shipped with the standard bootloader to the UF2 bootloader without an external programmer. This is performed by simply downloading and running a bootloader update file using an application called “Bossa” (described below), then following the UF2 Bootloader Upload Instructions, to upload the newest firmware version.

Warning: This code replaces the standard bootloader shipped on older Falcon boards without the need to resort to an external programmer. However, if this process fails for whatever reason, it will render your board unable to either upload new code over the USB port or run as a flight controller. Recovery is then only possible with an external programmer via the Falcon’s SWD debug port. Therefore following this procedure is NOT recommended, unless you have access to one of the following programmers:

  • Atmel ICE (In Circuit Emulator)
  • EDBG
  • mEDBG
  • Power Debugger
  • J-Link
  • J-Link over IP
  • J-Link ARM-Pro
  • J-Link Ultra

Note: The Falcon 1 and 2 updates will be avaliable in both binary (.bin) and UF2 (.uf2) formats for either the standard or UF2 bootloader.


Uploading the UF2 Bootloader to the Falcon boards requires only an A to micro B USB cable, to connect it to a laptop or PC.

Uploading The UF2 Bootloader

To upload the latest firmware to your Falcon board, please follow these upload instructions:

  1. Warning: Please first remove the aircraft’s propellers.
  2. Download the appropriate Falcon UF2 Update .bin for either the Falcon 1 or 2 and copy it to your desired directory/folder location:

    Falcon 1 UF2 Bootloader V3.7.0.bin Falcon 2 UF2 Bootloader V3.7.0.bin
  3. Go to the following webpage: https://github.com/shumatech/BOSSA/releases.
  4. Download the appropriate Bossa 1.8 application for your platform:
  5. Windows x86 (32-bit) installer: https://github.com/shumatech/BOSSA/releases/download/1.8/bossa-x86-1.8.msi.zip
    Window x64 (64-bit) installer: https://github.com/shumatech/BOSSA/releases/download/1.8/bossa-x64-1.8.msi.zip
    Apple Mac OS X installer: https://github.com/shumatech/BOSSA/releases/download/1.8/bossa-1.8.dmg.zip

  6. Unzip/extract the file and install the Bossa application.
  7. Launch the Bossa application (double click on “Bossa.exe”), as shown in the image below:
  8. Bossa

  9. Unplug your multi-rotor battery (if connected), then connect the micro USB cable to the Falcon’s micro USB port.
  10. Falcon USB

  11. Connect the other end to the PC/laptop, this will power up the board. This is OK, even with the ESCs attached, although if you’re using the low voltage battery alarm, you may have to set the alarm voltage and trim (in the Miscellaneous Settings menu) to zero to silence it). You should hear a device connection tone on the PC. If the flight controller hasn’t been connected before, it may need some time to search for the required drivers.
  12. Double tap the Falcon’s reset button, (two presses in quick succession), this puts the Falcon into bootloader mode. The board will reboot, the OLED display however should remain blank. You may hear the PC device disconnection and connection tones, as the flight controller switches COM port to transfer control to its bootloader.
  13. In the Bossa application press the “Refresh” button and select the COM port from the drop down list.
  14. Use the “Browse” button and select the Falcon’s binary (.bin) file, downloaded from the Flitetronix website (in step 2 above).
  15. In the Bossa application check the boxes “Erase All” and “Boot to flash”, as shown in the image above.
  16. Select the “Info” button to ensure that Falcon’s processor is responding, as shown in the image below. Click on OK to close this pop-up dialog box.
  17. BossaInfo

  18. In the Bossa application, click on the “Write” button.
  19. If the write has been successful then click on the “Verify” button.
  20. Close the Bossa application.
  21. Unplug the USB cable from your the PC/laptop and plug it back in again. The ARMED LED will flash for 1 second.
  22. Double tap the reset button. The drive “FALCONxBOOT” should appear on your computer and the ARMED LED will pulse.
  23. Follow the UF2 Bootloader Upload Instructions, to upload the Falcon’s UF2 flight controller firmware.

Should you encounter difficulties during the upload process or require technical assistance then please contact us.