Provide an example on multiscreen scrolling

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 62 insertions, 0 deletions

diff --git a/scroll/include/reset.s b/scroll/include/reset.s
new file mode 100644
index 0000000..2402795
--- /dev/null
+++ b/scroll/include/reset.s
@@ -0,0 +1,62 @@
+;; Check `basics/sprite.s` for a deeper look on the logic below.
+.proc reset
+    sei
+    cld
+
+    ldx #$40
+    stx APU::FRAME_COUNTER
+
+    ldx #$FF
+    txs
+
+    inx
+    stx PPU::CONTROL
+    stx PPU::MASK
+    stx APU::DMC
+
+@vblankwait1:
+    bit PPU::STATUS
+    bpl @vblankwait1
+
+    ldx #0
+    lda #0
+@ram_reset_loop:
+    sta $000, x
+    sta $100, x
+    sta $300, x
+    sta $400, x
+    sta $500, x
+    sta $600, x
+    sta $700, x
+    inx
+    bne @ram_reset_loop
+
+    lda #$EF
+@sprite_reset_loop:
+    sta $200, x
+    inx
+    bne @sprite_reset_loop
+
+    lda #$00
+    sta OAM::ADDR
+    lda #$02
+    sta OAM::DMA
+
+@vblankwait2:
+    bit PPU::STATUS
+    bpl @vblankwait2
+
+    lda #$3F
+    sta PPU::ADDRESS
+    lda #$00
+    sta PPU::ADDRESS
+
+    lda #$0F
+    ldx #$20
+@palettes_reset_loop:
+    sta PPU::DATA
+    dex
+    bne @palettes_reset_loop
+
+    jmp main
+.endproc