如何在asm中为MOS 6502创建延迟

Question

我是ASM的新手，我试图解决如何为以下代码创建延迟：

org $1000

loop: inc $d021
    jmp loop

Answer 1

我想评论已经很清楚了。

每帧更改颜色的代码示例(1/50秒)

        sei       ; enable interrupts

loop1:  lda #$fb  ; wait for vertical retrace
loop2:  cmp $d012 ; until it reaches 251th raster line ($fb)
        bne loop2 ; which is out of the inner screen area

        inc $d021 ; increase background color

        lda $d012 ; make sure we reached
loop3:  cmp $d012 ; the next raster line so next time we
        beq loop3 ; should catch the same line next frame

        jmp loop1 ; jump to main loop

每秒钟更换颜色的代码示例

counter = $fa ; a zeropage address to be used as a counter

        lda #$00    ; reset
        sta counter ; counter

        sei       ; enable interrupts

loop1:  lda #$fb  ; wait for vertical retrace
loop2:  cmp $d012 ; until it reaches 251th raster line ($fb)
        bne loop2 ; which is out of the inner screen area

        inc counter ; increase frame counter
        lda counter ; check if counter
        cmp #$32    ; reached 50
        bne out     ; if not, pass the color changing routine

        lda #$00    ; reset
        sta counter ; counter

        inc $d021 ; increase background color
out:
        lda $d012 ; make sure we reached
loop3:  cmp $d012 ; the next raster line so next time we
        beq loop3 ; should catch the same line next frame

        jmp loop1 ; jump to main loop

Answer 2

例如：

loop: ldx $d021
      inx
      stx $d021
      cpx #100
      bne loop

Answer 3

这个怎么样？这应该会改变背景，等待4秒，然后再改变它。永远重复。

注意，您可以将秒数从0更改为255。

这是针对NTSC机器的，但是您可以将60更改为50 for PAL。

main:
    inc $D021

    ldx #4          //  Wait 4 seconds
loop1:
    ldy #60
loop2:

waitvb:
    bit $D011
    bpl waitvb
waitvb2:
    bit $D011
    bmi waitvb2

    dey
    bne loop2
    dex
    bne loop1

    jmp main