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
|
// Game_Music_Emu 0.5.5. http://www.slack.net/~ant/
#include "Kss_Scc_Apu.h"
/* Copyright (C) 2006 Shay Green. This module is free software; you
can redistribute it and/or modify it under the terms of the GNU Lesser
General Public License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version. This
module is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
details. You should have received a copy of the GNU Lesser General Public
License along with this module; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */
#include "blargg_source.h"
// Tones above this frequency are treated as disabled tone at half volume.
// Power of two is more efficient (avoids division).
unsigned const inaudible_freq = 16384;
int const wave_size = 0x20;
void Scc_Apu::run_until( blip_time_t end_time )
{
for ( int index = 0; index < osc_count; index++ )
{
osc_t& osc = oscs [index];
Blip_Buffer* const output = osc.output;
if ( !output )
continue;
output->set_modified();
blip_time_t period = (regs [0x80 + index * 2 + 1] & 0x0F) * 0x100 +
regs [0x80 + index * 2] + 1;
int volume = 0;
if ( regs [0x8F] & (1 << index) )
{
blip_time_t inaudible_period = (blargg_ulong) (output->clock_rate() +
inaudible_freq * 32) / (inaudible_freq * 16);
if ( period > inaudible_period )
volume = (regs [0x8A + index] & 0x0F) * (amp_range / 256 / 15);
}
BOOST::int8_t const* wave = (BOOST::int8_t*) regs + index * wave_size;
if ( index == osc_count - 1 )
wave -= wave_size; // last two oscs share wave
{
int amp = wave [osc.phase] * volume;
int delta = amp - osc.last_amp;
if ( delta )
{
osc.last_amp = amp;
synth.offset( last_time, delta, output );
}
}
blip_time_t time = last_time + osc.delay;
if ( time < end_time )
{
if ( !volume )
{
// maintain phase
blargg_long count = (end_time - time + period - 1) / period;
osc.phase = (osc.phase + count) & (wave_size - 1);
time += count * period;
}
else
{
int phase = osc.phase;
int last_wave = wave [phase];
phase = (phase + 1) & (wave_size - 1); // pre-advance for optimal inner loop
do
{
int amp = wave [phase];
phase = (phase + 1) & (wave_size - 1);
int delta = amp - last_wave;
if ( delta )
{
last_wave = amp;
synth.offset( time, delta * volume, output );
}
time += period;
}
while ( time < end_time );
osc.phase = phase = (phase - 1) & (wave_size - 1); // undo pre-advance
osc.last_amp = wave [phase] * volume;
}
}
osc.delay = time - end_time;
}
last_time = end_time;
}
|
