// --------------------------------------------------------------------------- // This file is part of reSID, a MOS6581 SID emulator engine. // Copyright (C) 2002 Dag Lem // // 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 __ENVELOPE_H__ #define __ENVELOPE_H__ #include "siddefs.h" RESID_NAMESPACE_START // ---------------------------------------------------------------------------- // A 16 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 in the attack state, and is // successively set to 1, 2, 4, 8, 16, 30 at the envelope counter values // 255, 93, 54, 26, 14, 6 in the decay and release states. // ---------------------------------------------------------------------------- class EnvelopeGenerator { public: EnvelopeGenerator(); RESID_INLINE void clock(); RESID_INLINE void clock(cycle_count delta_t); void reset(); void writeCONTROL_REG(reg8); void writeATTACK_DECAY(reg8); void writeSUSTAIN_RELEASE(reg8); reg8 readENV(); // 8-bit envelope output. RESID_INLINE reg8 output(); protected: reg16 rate_counter; reg16 rate_period; reg16 exponential_counter; reg8 envelope_counter; bool hold_zero; reg4 attack; reg4 decay; reg4 sustain; reg4 release; reg8 gate; enum { ATTACK, DECAY_SUSTAIN, RELEASE } state; // Lookup table to convert from attack, decay, or release value to rate // counter period. static reg16 rate_counter_period[]; // Lookup table to directly, from the envelope counter, find the current // exponential counter period. static reg8 exponential_counter_period[]; // The 16 selectable sustain levels. static reg8 sustain_level[]; friend class SID; }; // ---------------------------------------------------------------------------- // Inline functions. // The following functions are defined inline because they are called every // time a sample is calculated. // ---------------------------------------------------------------------------- #if RESID_INLINING || defined(__ENVELOPE_CC__) // ---------------------------------------------------------------------------- // SID clocking - 1 cycle. // ---------------------------------------------------------------------------- RESID_INLINE void EnvelopeGenerator::clock() { // Check for ADSR delay bug. // If the rate counter comparison value is set below the current value of the // rate counter, the counter will continue counting up to 2^15 = 0x8000, // and then count rate_period twice before the envelope can finally be // stepped. In this process one extra rate_counter step is taken. // This has been verified by sampling ENV3. // A possible explanation for this behavior is that the 16 bit rate counter // is compared with a 15 bit comparator for reset and with a 16 bit // comparator for envelope steps. // if ((++rate_counter & 0x7fff) != rate_period) { return; } if (rate_counter & 0x8000) { rate_counter = 1; 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[envelope_counter]) { 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; 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; } // When the envelope counter is changed to zero, it is frozen at zero. // This has been verified by sampling ENV3. // if (envelope_counter == 0) { hold_zero = true; } } } // ---------------------------------------------------------------------------- // SID clocking - delta_t cycles. // ---------------------------------------------------------------------------- RESID_INLINE void EnvelopeGenerator::clock(cycle_count delta_t) { // Check for ADSR delay bug. // If the rate counter comparison value is set below the current value of the // rate counter, the counter will continue counting up to 2^15 = 0x8000, // and then count rate_period twice before the envelope can finally be // stepped. In this process one extra rate_counter step is taken. // This has been verified by sampling ENV3. // A possible explanation for this behavior is that the 16 bit rate counter // is compared with a 15 bit comparator for reset and with a 16 bit // comparator for envelope steps. // reg16 rate_counter_15 = rate_counter & 0x7fff; // NB! This requires two's complement integer. int rate_step = rate_period - rate_counter_15; if (rate_step < 0) { rate_step += 0x8000; } for (; delta_t; rate_step = rate_period) { if (delta_t < rate_step) { rate_counter += delta_t; return; } if ((rate_counter + rate_step) & 0x8000) { rate_counter = 1; delta_t -= rate_step; rate_step = rate_period - 1; continue; } rate_counter = 0; delta_t -= rate_step; // 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[envelope_counter]) { exponential_counter = 0; // Check whether the envelope counter is frozen at zero. if (hold_zero) { continue; } 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; rate_period = rate_counter_period[decay]; rate_step = rate_period; } 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; } // When the envelope counter is changed to zero, it is frozen at zero. // This has been verified by sampling ENV3. // if (envelope_counter == 0) { hold_zero = true; } } } } // ---------------------------------------------------------------------------- // Read the envelope generator output. // ---------------------------------------------------------------------------- RESID_INLINE reg8 EnvelopeGenerator::output() { return envelope_counter; } #endif // RESID_INLINING || defined(__ENVELOPE_CC__) RESID_NAMESPACE_STOP #endif // not __ENVELOPE_H__