snes-asm/homebrew-tutorial/main.asm

.p816
.smart

.include "macros.inc"
.include "registers.inc"
.include "keys.inc"

.include "header.asm"

.segment "ZEROPAGE"

nmi_count:  .res 2

.segment "CODE"

VRAM_CHARS = $0000
VRAM_BG1 = $1000

start:
    .include "init.asm"

    ; Set up the color palette
    stz CGADD

    ; Color 0 - black
    lda #$00
    sta CGDATA
    lda #$00
    sta CGDATA

    ; Color 1 - red
    lda #$1f
    sta CGDATA
    lda #$00
    sta CGDATA

    ; Color 2 - green
    lda #$e0
    sta CGDATA
    lda #$03
    sta CGDATA

    ; Color 3 - blue
    lda #$00
    sta CGDATA
    lda #$7c
    sta CGDATA

    ; Graphics mode 0, 8x8 tiles
    stz BGMODE

    ; Set BG1 and tile map and character data
    lda #>VRAM_BG1
    sta BG1SC
    lda #VRAM_CHARS
    sta BG12NBA

    ; Load character data into VRAM
    lda #$80
    sta VMAIN
    ldx #VRAM_CHARS
    stx VMADDL
@charset_loop:
    lda charset,x
    sta VMDATAL
    inx
    lda charset,x
    sta VMDATAH
    inx
    cpx #(charset_end - charset)
    bne @charset_loop

; Manually clear screen
    ldx #(VRAM_BG1)
@loop:
    stx VMADDL
    lda #$00
    sta VMDATAL
    stz VMDATAH
    inx
    cpx #(VRAM_BG1 + 32 * 29)
    bne @loop

    ; write tile to position (1, 1)
    TILE_X = 1
    TILE_Y = 1
    ldx #(VRAM_BG1 + (TILE_Y * 32) + TILE_X)
    stx VMADDL
    lda #$01    ; tile number
    sta VMDATAL
    stz VMDATAH

    ; Show bg1
    lda #%00000001
    sta TM

    lda #$0f
    sta INIDISP

    lda #%10000001
    sta NMITIMEN

mainloop:

    lda nmi_count
    nmi_check:
        wai
        cmp nmi_count
        beq nmi_check


    lda JOY1L
    bit #JOYL_L
    beq down_not_pressed
        ; write tile 2 to position (4, 8)
        TILE_X2= 4
        TILE_Y2= 8
        ldx #(VRAM_BG1 + (TILE_Y2* 32) + TILE_X2)
        stx VMADDL
        lda #$02
        sta VMDATAL
        stz VMDATAH
    down_not_pressed:

    bra mainloop

busywait:
    bra busywait

nmi:
    bit RDNMI
    inc nmi_count
_rti:
    rti

.include "charset.asm"