First we need to delete the content of the eMMC on the radxa zero. We first install the following
sudo pip3 install pyamlboot
Then connect the board while pressing and holding the USB BOOT button on the back of the board (for more information check https://wiki.radxa.com/Zero/dev/maskrom). You can then run lsusb to confirm the device is indeed in maskrom mode:
Bus 001 Device 048: ID 1b8e:c003 Amlogic, Inc. GX-CHIP
After that you run
wget https://dl.radxa.com/zero/images/loader/radxa-zero-erase-emmc.bin
sudo boot-g12.py radxa-zero-erase-emmc.bin
in order to erase the eMMC so the board boots from the SD card.
Make sure to have available the latest version of Buildroot somewhere:
git clone --depth 1 https://github.com/buildroot/buildroot.git
Then, within this repo you should run
./setup.zero.sh ${buildroot_repo_path}
cd ${buildroot_repo_path}
make
Finally, to burn the resulting image:
sudo dd if=output/images/sdcard.img of=${path_to_your_sdcard} conv=fsync,notrunc bs=10M status=progress