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.
When a valid command is recieved, the carry flag should be inverted.
INTERFACE_UNLOCK: 0
Unlock the interface. No commands will be acknowledged until this is sent.
Parameters:
- bdehl: Must contain "emuif" in their respective order.
lb bc, "e", INTERFACE_UNLOCK
lb de, "m", "u"
lb hl, "i", "f"
ld c, c
INTERFACE_GIVE_ACHIEVEMENT: 1
Awards an achievement to the player.
Parameters:
- b: ID of achievement to award.
lb bc, ACHIEVEMENT_ID, INTERFACE_GIVE_ACHIEVEMENT
ld c, c
INTERFACE_SET_PRESENCE: 2
Set a "presence string" describing the user's status, such as their current level. This could be seen for example in Discord, when viewing a user's profile while they are playing a game. This string may be at most 256 bytes, beyond this the interface is expected to assume the terminator byte is missing and subsequently cancel the command.
Parameters:
- b: Bank of presence string; may refer to ROM, WRAM, or SRAM
- de: Pointer to 0-terminated presence string
ld bc, BANK(PresenceString), INTERFACE_SET_PRESENCE
ld de, PresenceString
ld c, c
This could be used to include interface defines in your project.
IF !DEF(INTERFACE_INC)
DEF INTERFACE_INC EQU 1
RSRESET
DEF INTERFACE_UNLOCK RB 1
DEF INTERFACE_GIVE_ACHIEVEMENT RB 1
DEF INTERFACE_SET_PRESENCE RB 1
MACRO interface_unlock
ld bc, "e" << 8 | INTERFACE_UNLOCK
ld de, "m" << 8 | "u"
ld hl, "i" << 8 | "n"
ld c, c
ENDM
ENDC