156 lines
4 KiB
C++
156 lines
4 KiB
C++
/*
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* This file is part of libsidplayfp, a SID player engine.
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*
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* Copyright 2011-2020 Leandro Nini <drfiemost@users.sourceforge.net>
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* Copyright 2018 VICE Project
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* Copyright 2007-2010 Antti Lankila
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* Copyright 2004,2010 Dag Lem <resid@nimrod.no>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#define ENVELOPEGENERATOR_CPP
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#include "EnvelopeGenerator.h"
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namespace reSIDfp
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{
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/**
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* Lookup table to convert from attack, decay, or release value to rate
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* counter period.
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*
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* The rate counter is a 15 bit register which is left shifted each cycle.
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* When the counter reaches a specific comparison value,
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* the envelope counter is incremented (attack) or decremented
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* (decay/release) and the rate counter is resetted.
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*
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* see [kevtris.org](http://blog.kevtris.org/?p=13)
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*/
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const unsigned int EnvelopeGenerator::adsrtable[16] =
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{
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0x007f,
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0x3000,
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0x1e00,
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0x0660,
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0x0182,
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0x5573,
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0x000e,
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0x3805,
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0x2424,
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0x2220,
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0x090c,
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0x0ecd,
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0x010e,
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0x23f7,
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0x5237,
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0x64a8
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};
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void EnvelopeGenerator::reset()
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{
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// counter is not changed on reset
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envelope_pipeline = 0;
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state_pipeline = 0;
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attack = 0;
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decay = 0;
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sustain = 0;
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release = 0;
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gate = false;
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resetLfsr = true;
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exponential_counter = 0;
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exponential_counter_period = 1;
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new_exponential_counter_period = 0;
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state = RELEASE;
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counter_enabled = true;
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rate = adsrtable[release];
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}
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void EnvelopeGenerator::writeCONTROL_REG(unsigned char control)
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{
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const bool gate_next = (control & 0x01) != 0;
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if (gate_next != gate)
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{
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gate = gate_next;
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// The rate counter is never reset, thus there will be a delay before the
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// envelope counter starts counting up (attack) or down (release).
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if (gate_next)
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{
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// Gate bit on: Start attack, decay, sustain.
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next_state = ATTACK;
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state_pipeline = 2;
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if (resetLfsr || (exponential_pipeline == 2))
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{
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envelope_pipeline = (exponential_counter_period == 1) || (exponential_pipeline == 2) ? 2 : 4;
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}
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else if (exponential_pipeline == 1)
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{
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state_pipeline = 3;
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}
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}
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else
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{
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// Gate bit off: Start release.
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next_state = RELEASE;
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state_pipeline = envelope_pipeline > 0 ? 3 : 2;
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}
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}
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}
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void EnvelopeGenerator::writeATTACK_DECAY(unsigned char attack_decay)
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{
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attack = (attack_decay >> 4) & 0x0f;
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decay = attack_decay & 0x0f;
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if (state == ATTACK)
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{
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rate = adsrtable[attack];
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}
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else if (state == DECAY_SUSTAIN)
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{
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rate = adsrtable[decay];
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}
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}
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void EnvelopeGenerator::writeSUSTAIN_RELEASE(unsigned char sustain_release)
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{
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// From the sustain levels it follows that both the low and high 4 bits
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// of the envelope counter are compared to the 4-bit sustain value.
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// This has been verified by sampling ENV3.
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//
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// For a detailed description see:
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// http://ploguechipsounds.blogspot.it/2010/11/new-research-on-sid-adsr.html
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sustain = (sustain_release & 0xf0) | ((sustain_release >> 4) & 0x0f);
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release = sustain_release & 0x0f;
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if (state == RELEASE)
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{
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rate = adsrtable[release];
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}
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}
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} // namespace reSIDfp
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