island-story/src/input.s

INCLUDE "hardware.inc"

Section "Input Data", WRAM0

lastKeys:: db
keys:: db

Section "Input Code", ROM0

; Initialize input
; NOTE: Inline if needed
Keys_Init::
    ld hl, lastKeys
    xor a
    ld [hl+], a
    ld [hl], a

; Update the input state
Keys_Update::
    ld a, P1F_GET_BTN
    ld [rP1], a

    ; wait a few cycles
    ld a, [rP1]
    ld a, [rP1]

    ; extract btn bits into top of B
    cpl
    and $f
    swap a
    ld b, a
    ld a, P1F_GET_DPAD
    ld [rP1], a

    ; wait more cycles
    ld a, [rP1]
    ld a, [rP1]
    ld a, [rP1]
    ld a, [rP1]
    ld a, [rP1]
    ld a, [rP1]

    ; extract dpad bits into bottom of B
    cpl
    and $f
    or b
    ld b, a

    ; swap to use flag macros from hardware.inc
    ; TODO: optimize this code to avoid swap (very small win)
    swap b

    ; lastKeys <- keys ; keys <- B
    ld hl, keys
    ld a, [hl]
    ld [hl], b
    dec hl
    ld [hl], a

    ret