掌機 - Game Boy - Assembly - P1 Controller

參考資訊：
https://bgb.bircd.org/
https://github.com/gbdev/rgbds
https://github.com/sinamas/gambatte
https://github.com/lancekindle/DMGreport

電路圖


官方建議的讀取方式


main.s

IE          equ $ffff
IEF_VBLANK  equ %00000001
LCDC        equ $ff40
LCDCF_OBJ8  equ %00000000
LCDCF_OBJON equ %00000010
LCDCF_ON    equ %10000000
STAT        equ $ff41
STATF_BUSY  equ %00000010
P1          equ $ff00
P1_BUTTONS  equ %00100000
P1_ARROWS   equ %00010000
P1_DOWN     equ $80 
P1_UP       equ $40 
P1_LEFT     equ $20 
P1_RIGHT    equ $10 
P1_START    equ $08 
P1_SELECT   equ $04 
P1_B        equ $02 
P1_A        equ $01

section "vblank", rom0[$0040]
    reti
    
section "lcdc", rom0[$0048]
    reti
    
section "timer", rom0[$0050]
    reti
    
section "serial", rom0[$0058]
    reti
    
section "joypad", rom0[$0060]
    reti
    
section "entry", rom0[$0100]
    nop
    jp _start
    
section "header", rom0[$0104]
    db $ce, $ed, $66, $66, $cc, $0d, $00, $0b, $03, $73, $00, $83, $00, $0c, $00, $0d
    db $00, $08, $11, $1f, $88, $89, $00, $0e, $dc, $cc, $6e, $e6, $dd, $dd, $d9, $99
    db $bb, $bb, $67, $63, $6e, $0e, $ec, $cc, $dd, $dc, $99, $9f, $bb, $b9, $33, $3e
    db "0123456789abcde"
    db 0
    db 0, 0
    db 0
    db 0
    db 0
    db 0
    db 1
    db $33
    db 0
    db 0
    dw 0
    
_start:
    di
    ld sp, $ffff
    ld a, IEF_VBLANK
    ld [IE], a
    ei

    halt
    halt

    ld a, [LCDC]
    and ~LCDCF_ON
    ld [LCDC], a

    ld d, (8 * 9)
    ld bc, tile
    ld hl, $8000
copy_tile:
    ld a, [bc]
    ld [hl+], a
    ld [hl+], a
    inc bc
    dec d
    jr nz, copy_tile

    ld a, [LCDC]
    or LCDCF_ON
    ld [LCDC], a
 
loop:
    halt
    nop

    call get_key

    ld a, b
    and P1_UP
    jr nz, draw_up

    ld a, b
    and P1_DOWN
    jr nz, draw_down

    ld a, b
    and P1_LEFT
    jr nz, draw_left

    ld a, b
    and P1_RIGHT
    jr nz, draw_right

    ld a, b
    and P1_A
    jr nz, draw_a

    ld a, b
    and P1_B
    jr nz, draw_b

    ld a, b
    and P1_SELECT
    jr nz, draw_select

    ld a, b
    and P1_START
    jr nz, draw_start
    jp loop

draw_up:
    ld a, 1
    jr next

draw_down:
    ld a, 2
    jr next

draw_left:
    ld a, 4
    jr next

draw_right:
    ld a, 3
    jr next

draw_a:
    ld a, 5
    jr next

draw_b:
    ld a, 6
    jr next

draw_select:
    ld a, 7
    jr next

draw_start:
    ld a, 8
    jr next

next:
    call draw
    jp loop
 
draw:
    ld b, a
    ld hl, $9800
    ldh a, [STAT]
    and STATF_BUSY
    jr nz, @-4
    ld a, b
    ld [hl+], a
    ret

get_key:
    ld a, P1_BUTTONS
    ld [P1], a
    ld a, [P1]
    ld a, [P1]
    cpl
    and $0f
    swap a
    ld b, a
    ld a, P1_ARROWS
    ld [P1], a
    ld a, [P1]
    ld a, [P1]
    ld a, [P1]
    ld a, [P1]
    ld a, [P1]
    ld a, [P1]
    cpl
    and $0f
    or b
    ld b, a
    ld a, P1_BUTTONS | P1_ARROWS
    ld [P1], a
    ld a, b
    ret

tile:
    db %00000000
    db %00000000
    db %00000000
    db %00000000
    db %00000000
    db %00000000
    db %00000000
    db %00000000

    db %00011000
    db %00111100
    db %01111110
    db %00011000
    db %00011000
    db %00011000
    db %00011000
    db %00000000

    db %00011000
    db %00011000
    db %00011000
    db %00011000
    db %01111110
    db %00111100
    db %00011000
    db %00000000

    db %00000000
    db %00011000
    db %00001100
    db %11111110
    db %00001100
    db %00011000
    db %00000000
    db %00000000

    db %00000000
    db %00110000
    db %01100000
    db %11111110
    db %01100000
    db %00110000
    db %00000000
    db %00000000

    db %00110000
    db %01111000
    db %11001100
    db %11001100
    db %11111100
    db %11001100
    db %11001100
    db %00000000

    db %11111100
    db %01100110
    db %01100110
    db %01111100
    db %01100110
    db %01100110
    db %11111100
    db %00000000

    db %00111100
    db %01100110
    db %11000000
    db %11000000
    db %11000000
    db %01100110
    db %00111100
    db %00000000

    db %11111000
    db %01101100
    db %01100110
    db %01100110
    db %01100110
    db %01101100
    db %11111000
    db %00000000

完成