DTB was taken from https://github.com/avafinger/bananapi-zero-ubuntu-base-minimal/releases/download/v3.10/boot_focal.tar.gz and decompiled, then SPI interface was enabled according to https://github.com/avafinger/bananapi-zero-ubuntu-base-minimal/issues/49 .

DFL (Direct Firmware Loader) mode is a special boot environment where InkBox OS exports the entire MMC over USB storage. The user has 3 seconds from ~ when the green light starts blinking (kernel is loaded) to press both Home and Power buttons to enter DFL mode. If only one of these two or none at all is activated, the boot process continues as normal.

Causes OpenRC in rootfs chroot to behave strangely...

c.f. https://github.com/kobolabs/Kobo-Reader/issues/105

Little blue light staying put and nothing launches, complete system hang.
Why? It is a pure mystery, my friend.

This is a Secondary Program Loader initrd for InkBox. It permits you to switch between Nickel and InkBox at boot by kexec'ing a new kernel from userspace. Only Libra is supported currently, because kexec is actually reliable there.