path: root/src/libs/residfp/WaveformGenerator.h

/*
 * This file is part of libsidplayfp, a SID player engine.
 *
 * Copyright 2011-2022 Leandro Nini <drfiemost@users.sourceforge.net>
 * Copyright 2007-2010 Antti Lankila
 * Copyright 2004,2010 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

#ifndef WAVEFORMGENERATOR_H
#define WAVEFORMGENERATOR_H

#include "siddefs-fp.h"
#include "array.h"

namespace reSIDfp
{

/**
 * A 24 bit accumulator is the basis for waveform generation.
 * FREQ is added to the lower 16 bits of the accumulator each cycle.
 * The accumulator is set to zero when TEST is set, and starts counting
 * when TEST is cleared.
 *
 * Waveforms are generated as follows:
 *
 * - No waveform:
 * When no waveform is selected, the DAC input is floating.
 *
 *
 * - Triangle:
 * The upper 12 bits of the accumulator are used.
 * The MSB is used to create the falling edge of the triangle by inverting
 * the lower 11 bits. The MSB is thrown away and the lower 11 bits are
 * left-shifted (half the resolution, full amplitude).
 * Ring modulation substitutes the MSB with MSB EOR NOT sync_source MSB.
 *
 *
 * - Sawtooth:
 * The output is identical to the upper 12 bits of the accumulator.
 *
 *
 * - Pulse:
 * The upper 12 bits of the accumulator are used.
 * These bits are compared to the pulse width register by a 12 bit digital
 * comparator; output is either all one or all zero bits.
 * The pulse setting is delayed one cycle after the compare.
 * The test bit, when set to one, holds the pulse waveform output at 0xfff
 * regardless of the pulse width setting.
 *
 *
 * - Noise:
 * The noise output is taken from intermediate bits of a 23-bit shift register
 * which is clocked by bit 19 of the accumulator.
 * The shift is delayed 2 cycles after bit 19 is set high.
 *
 * Operation: Calculate EOR result, shift register, set bit 0 = result.
 *
 *                    reset  +--------------------------------------------+
 *                      |    |                                            |
 *               test--OR-->EOR<--+                                       |
 *                      |         |                                       |
 *                      2 2 2 1 1 1 1 1 1 1 1 1 1                         |
 *     Register bits:   2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 <---+
 *                          |   |       |     |   |       |     |   |
 *     Waveform bits:       1   1       9     8   7       6     5   4
 *                          1   0
 *
 * The low 4 waveform bits are zero (grounded).
 */
class WaveformGenerator
{
private:
    matrix_t* model_wave = nullptr;

    short* wave = nullptr;

    // PWout = (PWn/40.95)%
    unsigned int pw = 0;

    unsigned int shift_register = 0;

    /// Emulation of pipeline causing bit 19 to clock the shift register.
    int shift_pipeline = 0;

    unsigned int ring_msb_mask = 0;
    unsigned int no_noise = 0;
    unsigned int noise_output = 0;
    unsigned int no_noise_or_noise_output = 0;
    unsigned int no_pulse = 0;
    unsigned int pulse_output = 0;

    /// The control register right-shifted 4 bits; used for output function table lookup.
    unsigned int waveform = 0;

    unsigned int waveform_output = 0;

    /// Current accumulator value.
    unsigned int accumulator = 0;

    // Fout = (Fn*Fclk/16777216)Hz
    unsigned int freq = 0;

    /// 8580 tri/saw pipeline
    unsigned int tri_saw_pipeline = 0;

    /// The OSC3 value
    unsigned int osc3 = 0;

    /// Remaining time to fully reset shift register.
    unsigned int shift_register_reset = 0;

    // The wave signal TTL when no waveform is selected
    unsigned int floating_output_ttl = 0;

    /// The control register bits. Gate is handled by EnvelopeGenerator.
    //@{
    bool test = false;
    bool sync = false;
    //@}

    /// Tell whether the accumulator MSB was set high on this cycle.
    bool msb_rising = false;

    bool is6581 = false;
private:
    void clock_shift_register(unsigned int bit0);

    unsigned int get_noise_writeback();

    void write_shift_register();

    void set_noise_output();
    
    void set_no_noise_or_noise_output();

    void waveBitfade();

    void shiftregBitfade();

public:
    void setWaveformModels(matrix_t* models);

    /**
     * Set the chip model.
     * Must be called before any operation.
     *
     * @param is6581 true if MOS6581, false if CSG8580
     */
    void setModel(bool is6581) { this->is6581 = is6581; }

    /**
     * SID clocking.
     */
    void clock();

    /**
     * Synchronize oscillators.
     * This must be done after all the oscillators have been clock()'ed,
     * so that they are in the same state.
     *
     * @param syncDest The oscillator that will be synced
     * @param syncSource The sync source oscillator
     */
    void synchronize(WaveformGenerator* syncDest, const WaveformGenerator* syncSource) const;

    /**
     * Constructor.
     */
    WaveformGenerator() :
        model_wave(nullptr),
        wave(nullptr),
        pw(0),
        shift_register(0),
        shift_pipeline(0),
        ring_msb_mask(0),
        no_noise(0),
        noise_output(0),
        no_noise_or_noise_output(0),
        no_pulse(0),
        pulse_output(0),
        waveform(0),
        waveform_output(0),
        accumulator(0x555555),          // Accumulator's even bits are high on powerup
        freq(0),
        tri_saw_pipeline(0x555),
        osc3(0),
        shift_register_reset(0),
        floating_output_ttl(0),
        test(false),
        sync(false),
        msb_rising(false) {}

    /**
     * Write FREQ LO register.
     *
     * @param freq_lo low 8 bits of frequency
     */
    void writeFREQ_LO(unsigned char freq_lo) { freq = (freq & 0xff00) | (freq_lo & 0xff); }

    /**
     * Write FREQ HI register.
     *
     * @param freq_hi high 8 bits of frequency
     */
    void writeFREQ_HI(unsigned char freq_hi) { freq = (freq_hi << 8 & 0xff00) | (freq & 0xff); }

    /**
     * Write PW LO register.
     *
     * @param pw_lo low 8 bits of pulse width
     */
    void writePW_LO(unsigned char pw_lo) { pw = (pw & 0xf00) | (pw_lo & 0x0ff); }

    /**
     * Write PW HI register.
     *
     * @param pw_hi high 8 bits of pulse width
     */
    void writePW_HI(unsigned char pw_hi) { pw = (pw_hi << 8 & 0xf00) | (pw & 0x0ff); }

    /**
     * Write CONTROL REGISTER register.
     *
     * @param control control register value
     */
    void writeCONTROL_REG(unsigned char control);

    /**
     * SID reset.
     */
    void reset();

    /**
     * 12-bit waveform output.
     *
     * @param ringModulator The oscillator ring-modulating current one.
     * @return the waveform generator digital output
     */
    unsigned int output(const WaveformGenerator* ringModulator);

    /**
     * Read OSC3 value.
     */
    unsigned char readOSC() const { return static_cast<unsigned char>(osc3 >> 4); }

    /**
     * Read accumulator value.
     */
    unsigned int readAccumulator() const { return accumulator; }

    /**
     * Read freq value.
     */
    unsigned int readFreq() const { return freq; }

    /**
     * Read test value.
     */
    bool readTest() const { return test; }

    /**
     * Read sync value.
     */
    bool readSync() const { return sync; }
};

} // namespace reSIDfp

#if RESID_INLINING || defined(WAVEFORMGENERATOR_CPP)

namespace reSIDfp
{

RESID_INLINE
void WaveformGenerator::clock()
{
    if (unlikely(test))
    {
        if (unlikely(shift_register_reset != 0) && unlikely(--shift_register_reset == 0))
        {
            shiftregBitfade();

            // New noise waveform output.
            set_noise_output();
        }

        // The test bit sets pulse high.
        pulse_output = 0xfff;
    }
    else
    {
        // Calculate new accumulator value;
        const unsigned int accumulator_old = accumulator;
        accumulator = (accumulator + freq) & 0xffffff;

        // Check which bit have changed from low to high
        const unsigned int accumulator_bits_set = ~accumulator_old & accumulator;

        // Check whether the MSB is set high. This is used for synchronization.
        msb_rising = (accumulator_bits_set & 0x800000) != 0;

        // Shift noise register once for each time accumulator bit 19 is set high.
        // The shift is delayed 2 cycles.
        if (unlikely((accumulator_bits_set & 0x080000) != 0))
        {
            // Pipeline: Detect rising bit, shift phase 1, shift phase 2.
            shift_pipeline = 2;
        }
        else if (unlikely(shift_pipeline != 0) && --shift_pipeline == 0)
        {
            // bit0 = (bit22 | test) ^ bit17
            clock_shift_register(((shift_register << 22) ^ (shift_register << 17)) & (1 << 22));
        }
    }
}

RESID_INLINE
unsigned int WaveformGenerator::output(const WaveformGenerator* ringModulator)
{
    // Set output value.
    if (likely(waveform != 0))
    {
        const unsigned int ix = (accumulator ^ (~ringModulator->accumulator & ring_msb_mask)) >> 12;

        // The bit masks no_pulse and no_noise are used to achieve branch-free
        // calculation of the output value.
        waveform_output = wave[ix] & (no_pulse | pulse_output) & no_noise_or_noise_output;

        // Triangle/Sawtooth output is delayed half cycle on 8580.
        // This will appear as a one cycle delay on OSC3 as it is latched first phase of the clock.
        if ((waveform & 3) && !is6581)
        {
            osc3 = tri_saw_pipeline & (no_pulse | pulse_output) & no_noise_or_noise_output;
            tri_saw_pipeline = wave[ix];
        }
        else
        {
            osc3 = waveform_output;
        }

        // In the 6581 the top bit of the accumulator may be driven low by combined waveforms
        // when the sawtooth is selected
        if (is6581
                && (waveform & 0x2)
                && ((waveform_output & 0x800) == 0))
            accumulator &= 0x7fffff;

        write_shift_register();
    }
    else
    {
        // Age floating DAC input.
        if (likely(floating_output_ttl != 0) && unlikely(--floating_output_ttl == 0))
        {
            waveBitfade();
        }
    }

    // The pulse level is defined as (accumulator >> 12) >= pw ? 0xfff : 0x000.
    // The expression -((accumulator >> 12) >= pw) & 0xfff yields the same
    // results without any branching (and thus without any pipeline stalls).
    // NB! This expression relies on that the result of a boolean expression
    // is either 0 or 1, and furthermore requires two's complement integer.
    // A few more cycles may be saved by storing the pulse width left shifted
    // 12 bits, and dropping the and with 0xfff (this is valid since pulse is
    // used as a bit mask on 12 bit values), yielding the expression
    // -(accumulator >= pw24). However this only results in negligible savings.

    // The result of the pulse width compare is delayed one cycle.
    // Push next pulse level into pulse level pipeline.
    pulse_output = ((accumulator >> 12) >= pw) ? 0xfff : 0x000;

    return waveform_output;
}

} // namespace reSIDfp

#endif

#endif