WaveformGenerator.h

/*
 * This file is part of libsidplayfp, a SID player engine.
 *
 * Copyright 2011-2016 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"
 
#include "sidcxx11.h"
 
namespace reSIDfp
{
 
class WaveformGenerator
{
private:
    matrix_t* model_wave;
 
    short* wave;
 
    // PWout = (PWn/40.95)%
    unsigned int pw;
 
    unsigned int shift_register;
 
    int shift_pipeline;
 
    unsigned int ring_msb_mask;
    unsigned int no_noise;
    unsigned int noise_output;
    unsigned int no_noise_or_noise_output;
    unsigned int no_pulse;
    unsigned int pulse_output;
 
    unsigned int waveform;
 
    int floating_output_ttl;
 
    unsigned int waveform_output;
 
    unsigned int accumulator;
 
    // Fout  = (Fn*Fclk/16777216)Hz
    unsigned int freq;
 
    // 8580 tri/saw pipeline
    unsigned int tri_saw_pipeline;
    unsigned int osc3;
 
    int shift_register_reset;
 
    int model_shift_register_reset;
 
 
    bool test;
    bool sync;
 
    bool msb_rising;
 
    bool is6581;
 
    float dac[4096];
 
private:
    void clock_shift_register(unsigned int bit0);
 
    unsigned int get_noise_writeback();
 
    void write_shift_register();
 
    void reset_shift_register();
 
    void set_noise_output();
 
public:
    void setWaveformModels(matrix_t* models);
 
    void setChipModel(ChipModel chipModel);
 
    void clock();
 
    void synchronize(WaveformGenerator* syncDest, const WaveformGenerator* syncSource) const;
 
    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(no_noise | noise_output),
        no_pulse(0),
        pulse_output(0),
        waveform(0),
        floating_output_ttl(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),
        test(false),
        sync(false),
        msb_rising(false),
        is6581(true) {}
 
    void writeFREQ_LO(unsigned char freq_lo) { freq = (freq & 0xff00) | (freq_lo & 0xff); }
 
    void writeFREQ_HI(unsigned char freq_hi) { freq = (freq_hi << 8 & 0xff00) | (freq & 0xff); }
 
    void writePW_LO(unsigned char pw_lo) { pw = (pw & 0xf00) | (pw_lo & 0x0ff); }
 
    void writePW_HI(unsigned char pw_hi) { pw = (pw_hi << 8 & 0xf00) | (pw & 0x0ff); }
 
    void writeCONTROL_REG(unsigned char control);
 
    void reset();
 
    float output(const WaveformGenerator* ringModulator);
 
    unsigned char readOSC() const { return static_cast<unsigned char>(osc3 >> 4); }
 
    unsigned int readAccumulator() const { return accumulator; }
 
    unsigned int readFreq() const { return freq; }
 
    bool readTest() const { return test; }
 
    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))
        {
            reset_shift_register();
 
            // 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
        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
float 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
        // FIXME doesn't seem to always happen
        if ((waveform & 2) && unlikely(waveform & 0xd) && is6581)
            accumulator &= (waveform_output << 12) | 0x7fffff;
 
        write_shift_register();
    }
    else
    {
        // Age floating DAC input.
        if (likely(floating_output_ttl != 0) && unlikely(--floating_output_ttl == 0))
        {
            waveform_output = 0;
        }
    }
 
    // 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;
 
    // DAC imperfections are emulated by using waveform_output as an index
    // into a DAC lookup table. readOSC() uses waveform_output directly.
    return dac[waveform_output];
}
 
} // namespace reSIDfp
 
#endif
 
#endif