The bootloader provides an interface for the operating system providing various information.
Most importantly, these include the definition of the CallbackTable and its memory address as well as the definition of the contents of the backup register for the PowerManagement module.
The 64 byte CallbackTable contains information about the AMiRo-BLT version and several function pointers.
The former can be used to detect whether the installed bootloader corresponds to the interface or if a legacy version is installed (or none at all).
The latter shall be used as callbacks for restarting the system or shut down.
This way, the operating system is freed from most aspects of the Startup Shutdown Synchronization Protocol (SSSP).