1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
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
|
