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Diffstat (limited to 'lib/rbcodec/codecs/libgme/nes_vrc6_apu.c')
-rw-r--r--lib/rbcodec/codecs/libgme/nes_vrc6_apu.c192
1 files changed, 192 insertions, 0 deletions
diff --git a/lib/rbcodec/codecs/libgme/nes_vrc6_apu.c b/lib/rbcodec/codecs/libgme/nes_vrc6_apu.c
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+++ b/lib/rbcodec/codecs/libgme/nes_vrc6_apu.c
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1 // Nes_Snd_Emu 0.1.8. http://www.slack.net/~ant/
2
3#include "nes_vrc6_apu.h"
4
5/* Copyright (C) 2003-2006 Shay Green. This module is free software; you
6can redistribute it and/or modify it under the terms of the GNU Lesser
7General Public License as published by the Free Software Foundation; either
8version 2.1 of the License, or (at your option) any later version. This
9module is distributed in the hope that it will be useful, but WITHOUT ANY
10WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
11FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
12details. You should have received a copy of the GNU Lesser General Public
13License along with this module; if not, write to the Free Software Foundation,
14Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
15
16#include "blargg_source.h"
17
18void Vrc6_init( struct Nes_Vrc6_Apu* this )
19{
20 Synth_init( &this->saw_synth );
21 Synth_init( &this->square_synth );
22
23 Vrc6_output( this, NULL );
24 Vrc6_volume( this, (int)FP_ONE_VOLUME );
25 Vrc6_reset( this );
26}
27
28void Vrc6_reset( struct Nes_Vrc6_Apu* this )
29{
30 this->last_time = 0;
31 int i;
32 for ( i = 0; i < vrc6_osc_count; i++ )
33 {
34 struct Vrc6_Osc* osc = &this->oscs [i];
35 int j;
36 for ( j = 0; j < vrc6_reg_count; j++ )
37 osc->regs [j] = 0;
38 osc->delay = 0;
39 osc->last_amp = 0;
40 osc->phase = 1;
41 osc->amp = 0;
42 }
43}
44
45void Vrc6_output( struct Nes_Vrc6_Apu* this, struct Blip_Buffer* buf )
46{
47 int i;
48 for ( i = 0; i < vrc6_osc_count; i++ )
49 Vrc6_osc_output( this, i, buf );
50}
51
52void run_square( struct Nes_Vrc6_Apu* this, struct Vrc6_Osc* osc, blip_time_t end_time );
53void run_saw( struct Nes_Vrc6_Apu* this, blip_time_t end_time );
54static void Vrc6_run_until( struct Nes_Vrc6_Apu* this, blip_time_t time )
55{
56 require( time >= this->last_time );
57 run_square( this, &this->oscs [0], time );
58 run_square( this, &this->oscs [1], time );
59 run_saw( this, time );
60 this->last_time = time;
61}
62
63void Vrc6_write_osc( struct Nes_Vrc6_Apu* this, blip_time_t time, int osc_index, int reg, int data )
64{
65 require( (unsigned) osc_index < vrc6_osc_count );
66 require( (unsigned) reg < vrc6_reg_count );
67
68 Vrc6_run_until( this, time );
69 this->oscs [osc_index].regs [reg] = data;
70}
71
72void Vrc6_end_frame( struct Nes_Vrc6_Apu* this, blip_time_t time )
73{
74 if ( time > this->last_time )
75 Vrc6_run_until( this, time );
76
77 assert( this->last_time >= time );
78 this->last_time -= time;
79}
80
81void run_square( struct Nes_Vrc6_Apu* this, struct Vrc6_Osc* osc, blip_time_t end_time )
82{
83 struct Blip_Buffer* output = osc->output;
84 if ( !output )
85 return;
86
87 int volume = osc->regs [0] & 15;
88 if ( !(osc->regs [2] & 0x80) )
89 volume = 0;
90
91 int gate = osc->regs [0] & 0x80;
92 int duty = ((osc->regs [0] >> 4) & 7) + 1;
93 int delta = ((gate || osc->phase < duty) ? volume : 0) - osc->last_amp;
94 blip_time_t time = this->last_time;
95 if ( delta )
96 {
97 osc->last_amp += delta;
98 Blip_set_modified( output );
99 Synth_offset( &this->square_synth, time, delta, output );
100 }
101
102 time += osc->delay;
103 osc->delay = 0;
104 int period = Vrc6_osc_period( osc );
105 if ( volume && !gate && period > 4 )
106 {
107 if ( time < end_time )
108 {
109 int phase = osc->phase;
110 Blip_set_modified( output );
111
112 do
113 {
114 phase++;
115 if ( phase == 16 )
116 {
117 phase = 0;
118 osc->last_amp = volume;
119 Synth_offset( &this->square_synth, time, volume, output );
120 }
121 if ( phase == duty )
122 {
123 osc->last_amp = 0;
124 Synth_offset( &this->square_synth, time, -volume, output );
125 }
126 time += period;
127 }
128 while ( time < end_time );
129
130 osc->phase = phase;
131 }
132 osc->delay = time - end_time;
133 }
134}
135
136void run_saw( struct Nes_Vrc6_Apu* this, blip_time_t end_time )
137{
138 struct Vrc6_Osc* osc = &this->oscs [2];
139 struct Blip_Buffer* output = osc->output;
140 if ( !output )
141 return;
142 Blip_set_modified( output );
143
144 int amp = osc->amp;
145 int amp_step = osc->regs [0] & 0x3F;
146 blip_time_t time = this->last_time;
147 int last_amp = osc->last_amp;
148 if ( !(osc->regs [2] & 0x80) || !(amp_step | amp) )
149 {
150 osc->delay = 0;
151 int delta = (amp >> 3) - last_amp;
152 last_amp = amp >> 3;
153 Synth_offset( &this->saw_synth, time, delta, output );
154 }
155 else
156 {
157 time += osc->delay;
158 if ( time < end_time )
159 {
160 int period = Vrc6_osc_period( osc ) * 2;
161 int phase = osc->phase;
162
163 do
164 {
165 if ( --phase == 0 )
166 {
167 phase = 7;
168 amp = 0;
169 }
170
171 int delta = (amp >> 3) - last_amp;
172 if ( delta )
173 {
174 last_amp = amp >> 3;
175 Synth_offset( &this->saw_synth, time, delta, output );
176 }
177
178 time += period;
179 amp = (amp + amp_step) & 0xFF;
180 }
181 while ( time < end_time );
182
183 osc->phase = phase;
184 osc->amp = amp;
185 }
186
187 osc->delay = time - end_time;
188 }
189
190 osc->last_amp = last_amp;
191}
192
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