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Diffstat (limited to 'plugins/sid/sidplay-libs/resid/voice.cpp')
| -rw-r--r-- | plugins/sid/sidplay-libs/resid/voice.cpp | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/plugins/sid/sidplay-libs/resid/voice.cpp b/plugins/sid/sidplay-libs/resid/voice.cpp new file mode 100644 index 00000000..049e0530 --- /dev/null +++ b/plugins/sid/sidplay-libs/resid/voice.cpp @@ -0,0 +1,147 @@ +// --------------------------------------------------------------------------- +// This file is part of reSID, a MOS6581 SID emulator engine. +// Copyright (C) 2002 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" + +RESID_NAMESPACE_START + +// ---------------------------------------------------------------------------- +// Constructor. +// ---------------------------------------------------------------------------- +Voice::Voice() + : muted(false) +{ + 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_DC = -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_DC = -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(); +} + + +// ---------------------------------------------------------------------------- +// Voice mute. +// ---------------------------------------------------------------------------- +void Voice::mute(bool enable) +{ + // enable = true (means voice is muted) + muted = enable; +} + +RESID_NAMESPACE_STOP |