Crazflie 2.0 bootloader firmware that runs in the nRF51. See readme.md in crazyflie-nrf-firmware repos for more information about flash and boot architecture.
Just after clonning the repository:
./tools/fetch_dependencies.sh
This will dowsnload and patch the Nordic's nrf5 bootloader
In order to work on this bootloader you must have a debug probe and your Crazyflie fited with the nRF debug port from the debug adapter kit. This is because, the bootloader is part of the safe boot sequence of the Crazyflie and so flashing a non-functional bootloader will require a debug probe to get the Crazyflie back to work.
Once a stable version of the bootloader has been produced, it is possible to make an update binary that will flash both the bootloader and the bluetooth softdevice. This update binary can be flashed over radio like a normal firmware.
To compile you must hase arm-none-eabi- tools in the path, Python 3 and git.
Flashing requires a jlink debug probe and nrfjprog.
make
make flash
Check out the readme of the crazyflie-stm-bootloader repository to understand the interplay between the stm and nrf bootloaders.