.proc create_hdma_table
    ;it's OK to trash all registers here

    lda #0
    pha ;"done" flag on stack

    lda #127 ;there are 127 scanlines of data following
    tay
    ora #$80
    sta rainbow_hdma+0
    ldx #0 ;start offset
    lda #0

    loop:
    sta rainbow_hdma+1,x
    inc
    dey
    bne after
    inx
    inx
    jmp loop

    after:
    pla ;if set, we have gone through part 2
    beq part2

    ret

    part2:
    lda #1
    pha

    lda #97
    tay
    ora #$80
    sta rainbow_hdma+255
    ldx #256
    lda #128
    jmp loop
.endproc