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
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
|
;; NOTE: automatically generated by the build system.
.include "../config/generated.s"
.segment "HEADER"
;; Bytes 0-3: NES\0 magic header.
.byte 'N', 'E', 'S', $1A
;; Standard 32KB + 8KB NROM cartridge.
.byte $02, $01
;; Horizontal mirroring, no battery.
.byte $00
;; We use the NES 2.0 header mainly to differentiate between NTSC vs PAL in
;; a way that emulators won't ignore it.
.byte $08
;; Blanked out stuff.
.res $04, $00
;; NTSC vs PAL
.ifdef PAL
.byte $01
.else
.byte $00
.endif
;; Blanked out stuff.
.res $03, $00
.segment "CODE"
.include "../include/apu.s"
.include "../include/oam.s"
.include "../include/ppu.s"
.include "../include/asm.s"
.include "../include/joypad.s"
.include "../include/globals.s"
.include "../include/debug.s"
.include "assets.s"
.include "background.s"
.include "prng.s"
.include "explosions.s"
.include "player.s"
.include "enemies.s"
.include "bullets.s"
.include "title.s"
.include "driver.s"
.include "interrupts.s"
;; Pretty standard reset function, nothing crazy.
.proc reset
;; Disable interrupts and decimal mode.
sei
cld
;; Disable APU frame counter.
ldx #$40
stx APU::m_frame_counter
;; Setup the stack.
ldx #$FF
txs
;; Disable NMIs and the APU's DMC.
inx
stx PPU::m_control
stx PPU::m_mask
stx APU::m_dmc
;; First PPU wait.
bit PPU::m_status
@vblankwait1:
bit PPU::m_status
bpl @vblankwait1
;; Initialize the counter for frame drops before any NMIs can come in.
.ifdef PARTIAL
lda #0
sta Debug::zp_frame_drops
.endif
;; Reset all sprites by simply moving the Y coordinate out of screen.
lda #$EF
ldx #0
@sprite_reset_loop:
sta OAM::m_sprites, x
inx
inx
inx
inx
bne @sprite_reset_loop
;; DMA setup for sprite reset.
lda #$00
sta OAM::m_address
lda #$02
sta OAM::m_dma
;; Second PPU wait. After that the PPU is stable.
@vblankwait2:
bit PPU::m_status
bpl @vblankwait2
;; NOTE: palettes are not initialized here as it's going to be one of the
;; first things done on `main` code.
__fallthrough__ main
.endproc
.proc main
;; Disable the PPU and zero out variables which shadow PPU registers.
lda #0
sta PPU::m_mask
sta PPU::zp_mask
sta PPU::zp_control
;; Initialize other global variables which the rest of the game assume to
;; have zero as their initial values.
sta Globals::zp_flags
sta Joypad::zp_buttons1
sta Joypad::zp_buttons2
sta Player::zp_state
;; Initialize the level. We allow the build system to pass its own value for
;; this in `LEVEL`, just in case we want to debug the enemy of a specific
;; level.
.ifdef LEVEL
lda #LEVEL
sta Globals::zp_level
and #%00000111
sta Globals::zp_level_kind
.else
sta Globals::zp_level
sta Globals::zp_level_kind
.endif
;; Initialize the assets for the game.
jsr Assets::init
;; Initialize some PAL-specific constants.
.ifdef PAL
lda #0
sta Driver::zp_pal_counter
.endif
;; We shadow the PPU control register in memory. Depending on the `make`
;; target we might need to switch directly to the main game. Otherwise we go
;; into the title as expected.
.ifdef PARTIAL
jsr Driver::switch
lda PPU::zp_control
sta PPU::m_control
.else
jsr Title::init
lda #%10001000
sta PPU::zp_control
sta PPU::m_control
.endif
cli
;; Enable back the PPU
lda #%00011110
sta PPU::zp_mask
sta PPU::m_mask
@main_game_loop:
READ_JOYPAD1
lda Globals::zp_flags
and #%00000011
beq @title_screen
cmp #1
beq @game_screen
jmp @over
@title_screen:
;; If we are in a transitioning state, avoid the update from the title.
lda Globals::zp_flags
and #%00000100
bne @do_switch
jsr Title::update
beq @set_flags
@do_switch:
;; Start was pressed by the player, switch to the main game.
jsr Driver::switch
jmp @set_flags
@game_screen:
jsr Driver::update
__fallthrough__ @set_flags
@set_flags:
lda #%10000000
ora Globals::zp_flags
sta Globals::zp_flags
@wait_for_render:
bit Globals::zp_flags
bmi @wait_for_render
;; Rendering is done, we can perform another iteration of the loop!
jmp @main_game_loop
@over:
;; TODO: allow to start over, reset flags, control register, etc.
jmp @over
.endproc
.segment "VECTORS"
.addr nmi, reset, irq
|
