; =============================================================================
; joypad.asm - read the Game Boy joypad ($FF00) with edge detection.
; =============================================================================
INCLUDE "include/gbos.inc"

DEF rP1 EQU $FF00

DEF PAD_A      EQU $01
DEF PAD_B      EQU $02
DEF PAD_SELECT EQU $04
DEF PAD_START  EQU $08
DEF PAD_RIGHT  EQU $10
DEF PAD_LEFT   EQU $20
DEF PAD_UP     EQU $40
DEF PAD_DOWN   EQU $80

SECTION "pad_state", WRAM0
wPadCur::  DS 1       ; currently held (1 = pressed)
wPadPrev:: DS 1       ; held on the previous poll
wPadNew::  DS 1       ; newly pressed this poll (cur & ~prev)

SECTION "pad", ROM0

; read_joypad -> A = state, 1=pressed:
;   bit0 A, 1 B, 2 Select, 3 Start, 4 Right, 5 Left, 6 Up, 7 Down
read_joypad::
    ld a, $20                   ; P14=0: select d-pad
    ld [rP1], a
    ld a, [rP1]
    ld a, [rP1]                 ; let the lines settle
    cpl
    and $0F                     ; right/left/up/down (bits 0-3)
    swap a                      ; -> bits 4-7
    ld b, a
    ld a, $10                   ; P15=0: select buttons
    ld [rP1], a
    ld a, [rP1]
    ld a, [rP1]
    ld a, [rP1]
    ld a, [rP1]                 ; buttons bounce more; settle longer
    cpl
    and $0F                     ; A/B/Select/Start (bits 0-3)
    or b
    ld c, a
    ld a, $30                   ; deselect both
    ld [rP1], a
    ld a, c
    ret

; pad_poll - refresh wPadCur/wPadPrev/wPadNew.
pad_poll::
    ld a, [wPadCur]
    ld [wPadPrev], a
    call read_joypad
    ld [wPadCur], a
    ld b, a
    ld a, [wPadPrev]
    cpl
    and b                       ; newly pressed edges
    ld [wPadNew], a
    ret