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
|
// ---------------------------------------------------------------------------
// This file is part of reSID, a MOS6581 SID emulator engine.
// Copyright (C) 2004 Dag Lem <resid@nimrod.no>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
// ---------------------------------------------------------------------------
#define __VOICE_CC__
#include "voice.h"
// ----------------------------------------------------------------------------
// Constructor.
// ----------------------------------------------------------------------------
Voice::Voice()
{
set_chip_model(MOS6581);
}
// ----------------------------------------------------------------------------
// Set chip model.
// ----------------------------------------------------------------------------
void Voice::set_chip_model(chip_model model)
{
wave.set_chip_model(model);
if (model == MOS6581) {
// The waveform D/A converter introduces a DC offset in the signal
// to the envelope multiplying D/A converter. The "zero" level of
// the waveform D/A converter can be found as follows:
//
// Measure the "zero" voltage of voice 3 on the SID audio output
// pin, routing only voice 3 to the mixer ($d417 = $0b, $d418 =
// $0f, all other registers zeroed).
//
// Then set the sustain level for voice 3 to maximum and search for
// the waveform output value yielding the same voltage as found
// above. This is done by trying out different waveform output
// values until the correct value is found, e.g. with the following
// program:
//
// lda #$08
// sta $d412
// lda #$0b
// sta $d417
// lda #$0f
// sta $d418
// lda #$f0
// sta $d414
// lda #$21
// sta $d412
// lda #$01
// sta $d40e
//
// ldx #$00
// lda #$38 ; Tweak this to find the "zero" level
//l cmp $d41b
// bne l
// stx $d40e ; Stop frequency counter - freeze waveform output
// brk
//
// The waveform output range is 0x000 to 0xfff, so the "zero"
// level should ideally have been 0x800. In the measured chip, the
// waveform output "zero" level was found to be 0x380 (i.e. $d41b
// = 0x38) at 5.94V.
wave_zero = 0x380;
// The envelope multiplying D/A converter introduces another DC
// offset. This is isolated by the following measurements:
//
// * The "zero" output level of the mixer at full volume is 5.44V.
// * Routing one voice to the mixer at full volume yields
// 6.75V at maximum voice output (wave = 0xfff, sustain = 0xf)
// 5.94V at "zero" voice output (wave = any, sustain = 0x0)
// 5.70V at minimum voice output (wave = 0x000, sustain = 0xf)
// * The DC offset of one voice is (5.94V - 5.44V) = 0.50V
// * The dynamic range of one voice is |6.75V - 5.70V| = 1.05V
// * The DC offset is thus 0.50V/1.05V ~ 1/2 of the dynamic range.
//
// Note that by removing the DC offset, we get the following ranges for
// one voice:
// y > 0: (6.75V - 5.44V) - 0.50V = 0.81V
// y < 0: (5.70V - 5.44V) - 0.50V = -0.24V
// The scaling of the voice amplitude is not symmetric about y = 0;
// this follows from the DC level in the waveform output.
voice_DC = 0x800*0xff;
}
else {
// No DC offsets in the MOS8580.
wave_zero = 0x800;
voice_DC = 0;
}
}
// ----------------------------------------------------------------------------
// Set sync source.
// ----------------------------------------------------------------------------
void Voice::set_sync_source(Voice* source)
{
wave.set_sync_source(&source->wave);
}
// ----------------------------------------------------------------------------
// Register functions.
// ----------------------------------------------------------------------------
void Voice::writeCONTROL_REG(reg8 control)
{
wave.writeCONTROL_REG(control);
envelope.writeCONTROL_REG(control);
}
// ----------------------------------------------------------------------------
// SID reset.
// ----------------------------------------------------------------------------
void Voice::reset()
{
wave.reset();
envelope.reset();
}
|
