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
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
|
;****************************************************************************
; EntryPoint
; Where the program starts
;****************************************************************************
EntryPoint:
ld sp, RAM_Stack ; Init stack
xor a ; Reset Echo status
ld (RAM_Status), a
ld hl, $7F11 ; Mute PSG
ld (hl), $9F
ld (hl), $BF
ld (hl), $DF
ld (hl), $FF
xor a
ld (RAM_PSGData), a
ld (RAM_PSGData+16), a
ld (RAM_PSGData+32), a
ld (RAM_PSGData+48), a
ld hl, $6000 ; Set default bank
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld (hl), l
ld ix, $4000 ; YM2612 I/O ports base address
ld iyh, $40
exx ; Init PCM playback status
ld b, $00 ; Not playing
exx
ld (ix+0), $2B ; Disable DAC by default
ld (ix+1), $00
ld e, $7F ; Mute all FM channels
ld a, $40
ld b, 4
.mutefm:
ld (ix+0), a
ld (ix+1), e
ld (ix+2), a
ld (ix+3), e
inc a
ld (ix+0), a
ld (ix+1), e
ld (ix+2), a
ld (ix+3), e
inc a
ld (ix+0), a
ld (ix+1), e
ld (ix+2), a
ld (ix+3), e
inc a
inc a
djnz .mutefm
ld (ix+0), $B4 ; Ensure all channels can be heard from both
ld (ix+1), $C0 ; speakers (by default they're mute!)
ld (ix+0), $B5
ld (ix+1), $C0
ld (ix+0), $B6
ld (ix+1), $C0
ld (ix+2), $B4
ld (ix+3), $C0
ld (ix+2), $B5
ld (ix+3), $C0
ld (ix+2), $B6
ld (ix+3), $C0
ld (ix+0), $24 ; Init timers
ld (ix+1), $FE
ld (ix+0), $25
ld (ix+1), $03
ld (ix+0), $26
ld (ix+1), $C9
ld (ix+0), $27
ld (ix+1), $3F
jp IdleLoop ; Go into idle loop
;****************************************************************************
; PollPCM
; Used to update PCM while not idle
;****************************************************************************
PollPCM: macro
ld a, ($4000)
rrca
call c, UpdatePCM
endm
;****************************************************************************
; RunCommand
; Checks which command to run
;****************************************************************************
RunCommand:
dec a ; Command $01: load list
jp z, LoadList
dec a ; Command $02: play SFX
jp z, PlaySFX
dec a ; Command $03: stop SFX
jp z, StopSFXCmd
dec a ; Command $04: play BGM
jp z, PlayBGM
dec a ; Command $05: stop BGM
jp z, StopBGMCmd
dec a ; Command $06: resume BGM
jp z, ResumeBGM
PollPCM
xor a ; Bad command, ignore >:(
ld (RAM_Command), a
PollPCM
;****************************************************************************
; IdleLoop
; Loop that runs when not processing SFX or BGM
;****************************************************************************
IdleLoop:
ld a, (RAM_Command) ; Look for commands
or a
jr nz, RunCommand
PollPCM ; Poll PCM
ld a, ($4000) ; Tick?
bit 1, a
jr nz, DoTick
bit 0, a ; Poll PCM again
call nz, UpdatePCM ; Not using macro for optimization purposes
jp IdleLoop ; Keep idling
;****************************************************************************
; DoTick
; Called whenever a new tick triggers
;****************************************************************************
DoTick:
ld a, (ix+0)
bit 0, a
call nz, UpdatePCM
ld (ix+0), $27
ld (ix+1), $2F
PollPCM
DoTick_SFX: ; Process SFXs
jp DoTick_SFXSkip
DoTick_SFXSkip:
PollPCM
DoTick_BGM: ; Process BGMs
jp DoTick_BGMSkip
DoTick_BGMSkip:
PollPCM
jp UpdatePSG ; Update PSG envelopes
DoTick_PSGSkip:
PollPCM
jp IdleLoop ; End of subroutine
;****************************************************************************
; BankSwitch
; Switches into a new bank (won't update player status!)
;
; input A .... New bank to switch into
; input HL ... Must be $6000
; breaks ..... AF
;****************************************************************************
BankSwitch: macro
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
rrca
ld (hl), a
ld (hl), h
rrca
ld (hl), a
endm
;****************************************************************************
; LoadList [command $01]
; Loads the pointer list
;****************************************************************************
LoadList:
ld hl, RAM_ComBank ; Get command parameters
ld c, (hl)
inc l
ld e, (hl)
inc l
ld d, (hl)
ex de, hl
xor a ; Command parsed
ld (RAM_Command), a
ld de, RAM_PointerList ; Where the pointer list starts
.loop:
call GetParam ; Get high byte address
ld a, b ; Is it the end of the list?
or a
jp z, .end
ld (de), a ; Store high byte address
inc d
call GetParam ; Get low address byte
ld a, b
ld (de), a
inc d
call GetParam ; Get bank byte
ld a, b
ld (de), a
dec d ; Go for next byte
dec d
inc e
jp .loop
.end:
jp IdleLoop ; End of subroutine
;****************************************************************************
; GetParam
; Subroutine for getting the parameter byte
;****************************************************************************
GetParam:
ld a, (RAM_LastBank) ; Bank switch?
cp c
jp z, .noswitchp
ld a, c
ld (RAM_LastBank), a
push hl
ld hl, $6000
BankSwitch
pop hl
.noswitchp:
ld b, (hl) ; Get volume
inc l ; Get next address
jp nz, .nonewbankp
inc h
jp nz, .nonewbankp
ld h, $80
inc c
.nonewbankp:
ret ; End of subroutine
|
