scr_scroll

    ld de, (SCREEN_ADDR)
    ld b, 3
3:
    push bc
    ld a, 8
1:
    ld hl, 32
    add hl, de
    ld bc, 32 * 7
    push de
    ldir
    pop de
    inc d
    dec a
    jr nz, 1b
    push hl
    ld bc, -32 - 256 * 7
    add hl, bc
    ex de, hl
    ld a, 8
2:
    ld bc, 32
    push hl
    push de
    ldir
    pop de
    pop hl
    inc d
    inc h
    dec a
    jr nz, 2b
    pop de
    pop bc
    djnz 3b

    dec de
    ld h, d
    ld l, e
    ld a, 8
3:
    push hl
    push de
    ld (hl), b
    dec de
    ld bc, 31
    lddr
    pop de
    pop hl
    dec d
    dec h
    dec a
    jr nz, 3b

    ld de, (SCREEN_ATTR_ADDR)
    ld hl, 32
    add hl, de
    ld bc, 32 * 23
    ldir

    ld h, d
    ld l, e
    ld a, (ATTR_P)
    ld (hl), a
    inc de
    ld bc, 31
    ldir
    ret