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- // ---------------------------------------------------------------------------
- // 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
- // ---------------------------------------------------------------------------
-
- #ifndef __ENVELOPEFP_H__
- #define __ENVELOPEFP_H__
-
- #include "siddefsfp.h"
-
- extern float env_dac[256];
-
- // ----------------------------------------------------------------------------
- // A 15 bit counter is used to implement the envelope rates, in effect
- // dividing the clock to the envelope counter by the currently selected rate
- // period.
- // In addition, another counter is used to implement the exponential envelope
- // decay, in effect further dividing the clock to the envelope counter.
- // The period of this counter is set to 1, 2, 4, 8, 16, 30 at the envelope
- // counter values 255, 93, 54, 26, 14, 6, respectively.
- // ----------------------------------------------------------------------------
- class EnvelopeGeneratorFP
- {
- public:
- EnvelopeGeneratorFP();
-
- enum State { ATTACK, DECAY_SUSTAIN, RELEASE };
-
- inline void clock();
- void reset();
- void mute(bool enable);
-
- void writeCONTROL_REG(reg8);
- void writeATTACK_DECAY(reg8);
- void writeSUSTAIN_RELEASE(reg8);
- reg8 readENV();
-
- inline float output();
-
- protected:
- void set_nonlinearity(float nl);
- void update_rate_period(reg16 period);
-
- int rate_counter;
- int rate_period;
- reg8 exponential_counter;
- reg8 exponential_counter_period;
- reg8 envelope_counter;
- float envelope_counter_dac;
- bool hold_zero;
- bool muted;
-
- reg4 attack;
- reg4 decay;
- reg4 sustain;
- reg4 release;
-
- reg8 gate;
-
- State state;
-
- // Lookup table to convert from attack, decay, or release value to rate
- // counter period.
- static reg16 rate_counter_period[];
-
- // The 16 selectable sustain levels.
- static reg8 sustain_level[];
-
- friend class SIDFP;
- };
-
- // ----------------------------------------------------------------------------
- // SID clocking - 1 cycle.
- // ----------------------------------------------------------------------------
- inline
- void EnvelopeGeneratorFP::clock()
- {
- if (++ rate_counter != rate_period)
- return;
-
- rate_counter = 0;
-
- // The first envelope step in the attack state also resets the exponential
- // counter. This has been verified by sampling ENV3.
- //
- if (state == ATTACK || ++exponential_counter == exponential_counter_period)
- {
- exponential_counter = 0;
-
- // Check whether the envelope counter is frozen at zero.
- if (hold_zero) {
- return;
- }
-
- switch (state) {
- case ATTACK:
- // The envelope counter can flip from 0xff to 0x00 by changing state to
- // release, then to attack. The envelope counter is then frozen at
- // zero; to unlock this situation the state must be changed to release,
- // then to attack. This has been verified by sampling ENV3.
- //
- ++envelope_counter &= 0xff;
- if (envelope_counter == 0xff) {
- state = DECAY_SUSTAIN;
- update_rate_period(rate_counter_period[decay]);
- }
- break;
- case DECAY_SUSTAIN:
- if (envelope_counter != sustain_level[sustain]) {
- --envelope_counter;
- }
- break;
- case RELEASE:
- // The envelope counter can flip from 0x00 to 0xff by changing state to
- // attack, then to release. The envelope counter will then continue
- // counting down in the release state.
- // This has been verified by sampling ENV3.
- // NB! The operation below requires two's complement integer.
- //
- --envelope_counter &= 0xff;
- break;
- }
-
- // Check for change of exponential counter period.
- switch (envelope_counter) {
- case 0xff:
- exponential_counter_period = 1;
- break;
- case 0x5d:
- exponential_counter_period = 2;
- break;
- case 0x36:
- exponential_counter_period = 4;
- break;
- case 0x1a:
- exponential_counter_period = 8;
- break;
- case 0x0e:
- exponential_counter_period = 16;
- break;
- case 0x06:
- exponential_counter_period = 30;
- break;
- case 0x00:
- exponential_counter_period = 1;
-
- // When the envelope counter is changed to zero, it is frozen at zero.
- // This has been verified by sampling ENV3.
- hold_zero = true;
- break;
- }
-
- envelope_counter_dac = muted ? 0.f : env_dac[envelope_counter];
- }
- }
-
- // ----------------------------------------------------------------------------
- // Read the envelope generator output.
- // ----------------------------------------------------------------------------
- inline
- float EnvelopeGeneratorFP::output()
- {
- return envelope_counter_dac;
- }
-
- #endif // not __ENVELOPE_H__
-