Boot process

The calculator boot process is divided in multiple steps!

1. The first code loaded is the bootloader stored in the internal flash, verifying the signature of the kernel then loading it if it's valid
2. The kernel checks the signature of the userland, then load it in unprivileged mode if the signature valid.
3. The userland is loaded, and launch the onboarding screen (selection of the language and country), then drop the user into the home screen.

On unlocked calculators with custom bootloaders (Omega and Upsilon), the bootloader doesn't check the signature and kernel is not present (kernel is merged with the userland, and everything is running in privileged mode).