1 files changed, 76 insertions, 0 deletions
diff --git a/space/src/vectors/reset.s b/space/src/vectors/reset.s
new file mode 100644
index 0000000..afc9fa5
--- /dev/null
+++ b/space/src/vectors/reset.s
@@ -0,0 +1,76 @@
+.segment "CODE"
+
+reset:
+    ;; Ignore IRQs and disable decimal mode.
+    sei
+    cld
+
+    ;; Disable APU frame IRQ.
+    ldx #$40
+    stx APU::FRAME_COUNTER
+
+    ;; Set up the stack register with the proper value.
+    ldx #$ff
+    txs
+
+    ;; And now disable, in this order, NMI, rendering and DMC IRQs. Note that
+    ;; `x` was set to $ff, so increasing it by one results in a zero, which is
+    ;; the value then stored in the aforementioned memory locations.
+    inx
+    stx PPU::CONTROL
+    stx PPU::MASK
+    stx APU::DMC
+
+    ;;;
+    ;; NOTE: If you are using a mapper which needs some special configuration,
+    ;; now it would be a good time set it up. I am not using a special mapper,
+    ;; so there's nothing from me to do here.
+    ;;;
+
+    ;; First of the two VBLANK waits.
+@vblankwait1:
+    bit PPU::STATUS
+    bpl @vblankwait1
+
+    ;; Clear RAM memory. Notice that we are not clearing $200-$2ff, this is done
+    ;; later.
+    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 $700, x
+    inx
+    bne @ram_reset_loop
+
+    ;; Reset sprites by moving them off-screen.
+    lda #$ef
+@sprite_reset_loop:
+    sta $200, x
+    inx
+    bne @sprite_reset_loop
+
+    ;; Write "sprites" into OAM.
+    OAM_WRITE_SPRITES
+
+    ;; Last VBLANK wait.
+@vblankwait2:
+    bit PPU::STATUS
+    bpl @vblankwait2
+
+    ;; Reset palettes.
+    PPU_ADDR $3F00
+
+    lda #$0F
+    ldx #$20
+@palettes_reset_loop:
+    sta PPU::DATA
+    dex
+    bne @palettes_reset_loop
+
+    ;; Jump into the main subroutine.
+    jmp main