First day of advent of code

Signed-off-by: Miquel Sabaté Solà <msabate@suse.com>

1 files changed, 63 insertions, 0 deletions

diff --git a/include/reset.s b/include/reset.s
new file mode 100644
index 0000000..e68d3db
--- /dev/null
+++ b/include/reset.s
@@ -0,0 +1,63 @@
+;; Common `reset` procedure for NROM "games". Check `basics/sprite.s` on
+;; @mssola/NES for a proper explanation on the code (will be open soon,
+;; promise!).
+reset:
+    sei
+    cld
+
+    ldx #$40
+    stx $4017
+
+    ldx #$ff
+    txs
+
+    inx
+    stx $2000
+    stx $2001
+    stx $4010
+
+@vblankwait1:
+    bit $2002
+    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 $2003
+    lda #$02
+    sta $4014
+
+@vblankwait2:
+    bit $2002
+    bpl @vblankwait2
+
+    lda #$3F
+    sta $2006
+    lda #$00
+    sta $2006
+
+    lda #$0F
+    ldx #$20
+@palettes_reset_loop:
+    sta $2007
+    dex
+    bne @palettes_reset_loop
+
+    jmp main