If a Game Boy game is ever released on a platform such as Steam, it would be nice if the ROM could trivially interface with the platform's API. The goal of this document is to specify a simple, general-purpose interface that is non-intrusive and will run on both hardware and an emulator that implements the interface.
The interface works by filling CPU regs with a tiny bit of info about the command being given, and then executing ld c, c
to send the command. For example:
ld b, ACHIEVEMENT_ID
ld c, INTERFACE_GIVE_ACHIEVEMENT
ld c, c ; Tell the interface to give an achievement.