Almost have scrolling up working

src/main.s

@@ -62,16 +62,43 @@ start:
     and BTN_UP
     jr z, .down
 
+    ; don't scroll up if on last tile
+    ld hl, rSCY
+    ld a, [hl]
+    and %111
+    jr nz, .update_up
+
+    ld hl, CURRENT_CAMERA_Y
+    ld a, [hl]
+    or a
+    jr z, .vbl
+
+.update_up:
     ld hl, rSCY
     dec [hl]
+    call Map_Scroll
 
 .down:
     ld a, [keys]
     and BTN_DOWN
     jr z, .right
 
+    ; don't scroll down if on last tile
+    ld a, [rSCY]
+    and %111
+    jr nz, .update_down
+
+    ld a, [CURRENT_MAP_HEIGHT]
+    ld b, a
+    ld a, [CURRENT_CAMERA_Y]
+    add 18
+    cp b
+    jr z, .vbl
+
+.update_down:
     ld hl, rSCY
     inc [hl]
+    call Map_Scroll
 
 .right:
     ld a, [keys]
@@ -80,6 +107,7 @@ start:
 
     ld hl, rSCX
     inc [hl]
+    call Map_Scroll
 
 .left:
     ld a, [keys]

src/map.s

@@ -112,12 +112,131 @@ Map_Load::
 ; Update map state based on SCX/SCY
 Map_Scroll::
     ; Adjust CURRENT_CAMERA_X
-    ; Adjust CURRENT_CAMERA_Y
 
+;     ; Adjust CURRENT_CAMERA_Y if [LAST_SCY]/8 != [rSCY]/8
+;     ld a, [rSCY]
+;     srl a
+;     srl a
+;     srl a
+
+;     ld hl, LAST_SCY
+;     ld b, [hl]
+;     srl b
+;     srl b
+;     srl b
+
+;     cp b
+;     jr c, .cmp
+;     jr z, .scroll_up_check
+
+;     sub $20
+
+; .cmp:
+;     sub b
+
+;     ld hl, CURRENT_CAMERA_Y
+;     add [hl]
+;     ld [hl], a
+
+    ; min([LAST_SCY]/8 - [SCY/8], [SCY/8] - [LAST_SCY]/8)
+
+    ld a, [LAST_SCY]
+    srl a
+    srl a
+    srl a
+    ld b, a
+
+    ld a, [rSCY]
+    srl a
+    srl a
+    srl a
+
+    ; c <- scy/8 - last_scy/8
+    sub b
+    ld c, a
+
+    ld a, [rSCY]
+    srl a
+    srl a
+    srl a
+    ld b, a
+
+    ld a, [LAST_SCY]
+    srl a
+    srl a
+    srl a
+    sub b
+    ; a <- last_scy/8 - scy/8
+
+    cp c
+
+.tryit:
+    ld [CURRENT_CAMERA_Y], a
+
+.scroll_up_check:
     ; If SCY = PAGEY, write map row
     ; map coords = CURRENT_CAMERA_X, CURRENT_CAMERA_Y - 2
-    ; HL = _SCRN0 + 32 * (page_y - 1)
+    ; HL = _SCRN0 + 32 * (32 - page_y/8 - 2)
+    ld hl, PAGEY
+    ld a, [rSCY]
+    cp [hl]
+    jr nz, .scroll_down_check
 
+    ld a, [rSCX]
+    ld b, a
+    ld a, [CURRENT_CAMERA_X]
+    srl b
+    srl b
+    srl b
+    sub b
+    ld b, a
+
+    ld a, [CURRENT_CAMERA_Y]
+    cp 2
+    jr c, .done
+
+    sub 2
+    ld c, a
+
+    ; a = scy/8 + (scy/8 < 2 ? 30 : -2)
+
+    ld a, [rSCY]
+    srl a
+    srl a
+    srl a
+
+    cp 2
+    jr nc, .loop0
+    add 32
+
+.loop0:
+    sub 2
+
+    ; hl = _SCRN0 + 32 * a
+    ld e, a
+    ld hl, _SCRN0
+.loop:
+    ld a, e
+    or a
+    jr z, .write_up
+
+    ld a, 32
+    ADD16 hl
+
+    dec e
+    jr .loop
+
+.write_up:
+    halt
+    call write_map_row
+
+    ld a, [PAGEY]
+    sub 8
+    ld [PAGEY], a
+
+    jr .done
+
+.scroll_down_check:
     ; If SCY = SCRN_Y - PAGEY, write map row
     ; map coords = CURRENT_CAMERA_X, CURRENT_CAMERA_Y + 21
     ; HL = _SCRN0 + 32 * ((32 - page_y) - 1)
@@ -126,6 +245,11 @@ Map_Scroll::
     ; If SCX = PAGEX, write map col
     ; If SCX = SCRN_X - PAGEX, write map col
 
+.done:
+    ld hl, LAST_SCY
+    ld a, [rSCY]
+    ld [hl], a
+
     ret
 
 ; Write a row of map data into map RAM