tile scroll

vwait:
    ld a, (am_scrolling)
    cp 1
    jr nz, .noscroll
     call scrollScreenRight
.noscroll:
IRQBuffer: ds 5

scroll_progress: ds 2, 0
scroll_drawtarget: ds 2, 0
scroll_inc: ds 1, 1
am_scrolling: ds 1, 0
rowbuffer: ds 22, 0
newscreen_ofs: ds 1, 0

checkEdgeOfScreen:
        ld a, (SPRITE_OAM+1)
        cp 250
        ret c
         ld a, 3
         ld (P_MOVESTATE), a ; 3 = 'pause'
         ld a, 1
         ld (am_scrolling), a ; 1 = true, so do nothing except call scroll_screen
         ld hl, $1800
         ld (scroll_drawtarget), hl
         inc hl
         ld (scroll_progress), hl  ; 1801


scrollScreenRight:
        di

        ld hl, rowbuffer
.loop:
        push hl         ; rowbuffer to stack
        xor a           ; not above 2k! :)
        out ($99), a    ; bits 14-16
        ld a, 14+128    ; to r#14
        out ($99), a
        ld hl, (scroll_progress)
        ld a, l
        out ($99), a        ; low byte
        ld a, h             ; 1801
        out ($99), a        ; bits 8-13, read
        in a, ($98)
        pop bc              ; rowbuffer to bc
        push hl             ; progress to stack
        push bc             ; rowbuffer to stack
        pop hl              ; rowbuffer to hl
        ld (hl), a          ; first tile done: to rowbuffer
        pop hl              ; progress to hl
        push bc             ; rowbuffer to stack
        ld bc, $20
        add hl, bc
        ld a, h
        cp $1b
        jr z, .done
        ld (scroll_progress), hl
        pop hl
        inc hl
        jp .loop
.done:
        ld (scroll_progress), hl ; 1b01
        ld hl, rowbuffer
.loop2:
        ld de, (scroll_drawtarget) ; 1800
        xor a
        out ($99), a
        ld a, 14+128
        out ($99),a
        ld a, e
        out ($99), a
        ld a, d
        or %01000000
        out ($99), a
        ld a, (hl)
        out ($98), a
        inc hl
        push hl
        ld hl, $20
        add hl, de
        ld (scroll_drawtarget), hl
        ld a, h
        cp $1b
        jr z, .done2
        pop hl
        jp .loop2
.done2:
        ld a, (scroll_inc)
        cp 32
       jr z, .shiftdone
        ld hl, $1800
        ld bc, (scroll_inc)
        add hl, bc
        ld (scroll_drawtarget), hl
        inc c
        ld a, c
        ld (scroll_inc), a
        inc hl
        ld (scroll_progress), hl
        jp scrollScreenRight
.shiftdone:
        ld de, rowbuffer
        ld hl, screen2
        ld bc, (newscreen_ofs)
        push bc                 ; ---------------------------------v
        add hl, bc
        ld bc, 22
.ldnewloop:
        push bc
        ld a, (hl)
        ld (de), a
        ld bc, $20
        add hl, bc
        inc de
        pop bc
        dec bc
        jr z, .ldnewloop
        pop hl                  ; ---------------------------------^
        inc hl
        ld (newscreen_ofs), hl
        ld de, rowbuffer
        ld h, $18 + $40
        ld l, $31
.newrowdrawloop:
        push hl
        xor a
        out ($99), a
        ld a, 128+14
        out ($99), a
        ld a, l
        out ($99), a
        ld a, h
        out ($99), a
        push de
        pop hl
        ld a, (hl)
        out ($98), a
        ld bc, $20
        pop hl
        inc de
        ld a, h
        cp $5b
        jr nz, .newrowdrawloop
       ei
       ret