This firmware template is designed for development boards based around [STM32 F4 series micro-controller](https://www.st.com/en/microcontrollers-microprocessors/stm32f4-series.html).
There are two firmware images: `bootloader` and `application`.
The `bootloader` image allows to flash the `application` over USB using the DFU protocol.
The `bootloader` is started first and immediately jumps to the `application` if it is valid and the DFU mode is not forced (i.e. by pressing the user button on the board or requesting a DFU detach in the `application`).
The simplest way do flash the `bootloader` image is using the embedded bootloader.
By pressing the BOOT0 button (setting the pin low) while powering or resetting the device, the micro-controller boot its embedded UART/USB DFU bootloader.
Connect a USB cable and run `rake dfu_bootloader`.
Once the `bootloader` is flashed, it is possible to flash the `application` over USB using the DFU protocol by running `rake flash` (equivalent to `rake dfu_application`.
Note: I use my own DFU bootloader instead of the embedded bootloader because I was not able to start the embedded USB DFU bootloader from the application.
The images can also be flash using SWD (Serial Wire Debug) in case the firmware gets stuck and does not provide USB functionalities.
For that you need an SWD adapter.
The `Makefile` uses a ST-Link V2 programmer along OpenOCD software (default), or Black Magic Probe.