AY8910.cc

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/*
 * Emulation of the AY-3-8910
 *
 * Original code taken from xmame-0.37b16.1
 *   Based on various code snippets by Ville Hallik, Michael Cuddy,
 *   Tatsuyuki Satoh, Fabrice Frances, Nicola Salmoria.
 * Integrated into openMSX by ???.
 * Refactored in C++ style by Maarten ter Huurne.
 */

#include "AY8910.hh"
#include "AY8910Periphery.hh"
#include "DeviceConfig.hh"
#include "GlobalSettings.hh"
#include "MSXException.hh"
#include "Math.hh"
#include "StringOp.hh"
#include "serialize.hh"
#include "cstd.hh"
#include "likely.hh"
#include "outer.hh"
#include "random.hh"
#include <cassert>
#include <cstring>
#include <iostream>

using std::string;

namespace openmsx {

// The step clock for the tone and noise generators is the chip clock
// divided by 8; for the envelope generator of the AY-3-8910, it is half
// that much (clock/16).
constexpr float NATIVE_FREQ_FLOAT = (3579545.0f / 2) / 8;
constexpr int NATIVE_FREQ_INT = int(cstd::round(NATIVE_FREQ_FLOAT));

constexpr int PORT_A_DIRECTION = 0x40;
constexpr int PORT_B_DIRECTION = 0x80;

enum Register {
        AY_AFINE = 0, AY_ACOARSE = 1, AY_BFINE = 2, AY_BCOARSE = 3,
        AY_CFINE = 4, AY_CCOARSE = 5, AY_NOISEPER = 6, AY_ENABLE = 7,
        AY_AVOL = 8, AY_BVOL = 9, AY_CVOL = 10, AY_EFINE = 11,
        AY_ECOARSE = 12, AY_ESHAPE = 13, AY_PORTA = 14, AY_PORTB = 15
};

struct AY8910Tables {
        float YM2149Envelope[32];
        float AY8910Envelope[32];
        float volume[16];
};
static constexpr AY8910Tables calcTables()
{
        AY8910Tables tables = {};

        // Calculate the volume->voltage conversion table.
        // The AY-3-8910 has 16 levels, in a logarithmic scale (3dB per step).
        // YM2149 has 32 levels, the 16 extra levels are only used for envelope
        // volumes
        double out = 1.0;
        double factor = cstd::pow<5, 3>(0.5, 0.25); // 1/sqrt(sqrt(2)) ~= 1/(1.5dB)
        for (int i = 31; i > 0; --i) {
                tables.YM2149Envelope[i] = float(out);
                out *= factor;
        }
        tables.YM2149Envelope[0] = 0.0f;

        tables.volume[0] = 0.0f;
        for (int i = 1; i < 16; ++i) {
                tables.volume[i] = tables.YM2149Envelope[2 * i + 1];
        }

        // only 16 envelope steps, duplicate every step
        tables.AY8910Envelope[0] = 0.0f;
        tables.AY8910Envelope[1] = 0.0f;
        for (int i = 2; i < 32; i += 2) {
                tables.AY8910Envelope[i + 0] = tables.YM2149Envelope[i + 1];
                tables.AY8910Envelope[i + 1] = tables.YM2149Envelope[i + 1];
        }

        return tables;
}
constexpr AY8910Tables tables = calcTables();


// Perlin noise

static float noiseTab[256 + 3];

static void initDetune()
{
        auto& generator = global_urng(); // fast (non-cryptographic) random numbers
        std::uniform_real_distribution<float> distribution(-1.0f, 1.0f);

        for (int i = 0; i < 256; ++i) {
                noiseTab[i] = distribution(generator);
        }
        noiseTab[256] = noiseTab[0];
        noiseTab[257] = noiseTab[1];
        noiseTab[258] = noiseTab[2];
}
static float noiseValue(float x)
{
        // cubic hermite spline interpolation
        assert(0.0f <= x);
        int xi = int(x);
        float xf = x - xi;
        xi &= 255;
        float n0 = noiseTab[xi + 0];
        float n1 = noiseTab[xi + 1];
        float n2 = noiseTab[xi + 2];
        float n3 = noiseTab[xi + 3];
        float a = n3 - n2 + n1 - n0;
        float b = n0 - n1 - a;
        float c = n2 - n0;
        float d = n1;
        return ((a * xf + b) * xf + c) * xf + d;
}


// Generator:

inline void AY8910::Generator::reset()
{
        count = 0;
}

inline void AY8910::Generator::setPeriod(int value)
{
        // Careful studies of the chip output prove that it instead counts up from
        // 0 until the counter becomes greater or equal to the period. This is an
        // important difference when the program is rapidly changing the period to
        // modulate the sound.
        // Also, note that period = 0 is the same as period = 1. This is mentioned
        // in the YM2203 data sheets. However, this does NOT apply to the Envelope
        // period. In that case, period = 0 is half as period = 1.
        period = std::max(1, value);
        count = std::min(count, period - 1);
}

inline unsigned AY8910::Generator::getNextEventTime() const
{
        assert(count < period);
        return period - count;
}

inline void AY8910::Generator::advanceFast(unsigned duration)
{
        count += duration;
        assert(count < period);
}


// ToneGenerator:

AY8910::ToneGenerator::ToneGenerator()
{
        reset();
}

inline void AY8910::ToneGenerator::reset()
{
        Generator::reset();
        output = false;
}

int AY8910::ToneGenerator::getDetune(AY8910& ay8910)
{
        int result = 0;
        float vibPerc = ay8910.vibratoPercent.getDouble();
        if (vibPerc != 0.0f) {
                int vibratoPeriod = int(
                        NATIVE_FREQ_FLOAT /
                        float(ay8910.vibratoFrequency.getDouble()));
                vibratoCount += period;
                vibratoCount %= vibratoPeriod;
                result += int(
                        sinf((float(2 * M_PI) * vibratoCount) / vibratoPeriod)
                        * vibPerc * 0.01f * period);
        }
        float detunePerc = ay8910.detunePercent.getDouble();
        if (detunePerc != 0.0f) {
                float detunePeriod = NATIVE_FREQ_FLOAT /
                        float(ay8910.detuneFrequency.getDouble());
                detuneCount += period;
                float noiseIdx = detuneCount / detunePeriod;
                float detuneNoise = noiseValue(       noiseIdx)
                                  + noiseValue(2.0f * noiseIdx) / 2.0f;
                result += int(detuneNoise * detunePerc * 0.01f * period);
        }
        return std::min(result, period - 1);
}

inline void AY8910::ToneGenerator::advance(int duration)
{
        assert(count < period);
        count += duration;
        if (count >= period) {
                // Calculate number of output transitions.
                int cycles = count / period;
                count -= period * cycles; // equivalent to count %= period;
                output ^= cycles & 1;
        }
}

inline void AY8910::ToneGenerator::doNextEvent(AY8910& ay8910)
{
        if (unlikely(ay8910.doDetune)) {
                count = getDetune(ay8910);
        } else {
                count = 0;
        }
        output ^= 1;
}


// NoiseGenerator:

AY8910::NoiseGenerator::NoiseGenerator()
{
        reset();
}

inline void AY8910::NoiseGenerator::reset()
{
        Generator::reset();
        random = 1;
}

inline void AY8910::NoiseGenerator::doNextEvent()
{
        count = 0;

        // The Random Number Generator of the 8910 is a 17-bit shift register.
        // The input to the shift register is bit0 XOR bit3 (bit0 is the
        // output). Verified on real AY8910 and YM2149 chips.
        //
        // Fibonacci configuartion:
        //   random ^= ((random & 1) ^ ((random >> 3) & 1)) << 17;
        //   random >>= 1;
        // Galois configuration:
        //   if (random & 1) random ^= 0x24000;
        //   random >>= 1;
        // or alternatively:
        random = (random >> 1) ^ ((random & 1) << 13) ^ ((random & 1) << 16);
}

inline void AY8910::NoiseGenerator::advance(int duration)
{
        assert(count < period);
        count += duration;
        int cycles = count / period;
        count -= cycles * period; // equivalent to count %= period

        // The following loops advance the random state N steps at once. The
        // values for N (4585, 275, 68, 8, 1) are chosen so that:
        // - The formulas are relatively simple.
        // - The ratio between the step sizes is roughly the same.
        for (; cycles >= 4585; cycles -= 4585) {
                random = ((random & 0x1f) << 12)
                       ^ ((random & 0x1f) <<  9)
                       ^   random
                       ^ ( random         >>  5);
        }
        for (; cycles >= 275; cycles -= 275) {
                random = ((random & 0x03f) << 11)
                       ^ ((random & 0x1c0) <<  8)
                       ^ ((random & 0x1ff) <<  5)
                       ^   random
                       ^ ( random          >>  6)
                       ^ ( random          >>  9);
        }
        for (; cycles >= 68; cycles -= 68) {
                random = ((random & 0xfff) <<  5)
                       ^ ((random & 0xfff) <<  2)
                       ^   random
                       ^ ( random          >> 12);
        }
        for (; cycles >= 8; cycles -= 8) {
                random = ((random & 0xff) << 9)
                       ^ ((random & 0xff) << 6)
                       ^ ( random         >> 8);
        }
        for (; cycles >= 1; cycles -= 1) {
                random = ((random & 1) << 16)
                       ^ ((random & 1) << 13)
                       ^ ( random      >>  1);
        }
}


// Amplitude:

static bool checkAY8910(const DeviceConfig& config)
{
        string type = StringOp::toLower(config.getChildData("type", "ay8910"));
        if (type == "ay8910") {
                return true;
        } else if (type == "ym2149") {
                return false;
        } else {
                throw FatalError("Unknown PSG type: ", type);
        }
}

AY8910::Amplitude::Amplitude(const DeviceConfig& config)
        : isAY8910(checkAY8910(config))
{
        vol[0] = vol[1] = vol[2] = 0.0f;
        envChan[0] = false;
        envChan[1] = false;
        envChan[2] = false;
        envVolTable = isAY8910 ? tables.AY8910Envelope : tables.YM2149Envelope;

        if (0) {
                std::cout << "YM2149Envelope:";
                for (int i = 0; i < 32; ++i) {
                        std::cout << ' ' << std::hexfloat << tables.YM2149Envelope[i];
                }
                std::cout << "\nAY8910Envelope:";
                for (int i = 0; i < 32; ++i) {
                        std::cout << ' ' << std::hexfloat << tables.AY8910Envelope[i];
                }
                std::cout << "\nvolume:";
                for (int i = 0; i < 16; ++i) {
                        std::cout << ' ' << std::hexfloat << tables.volume[i];
                }
                std::cout << '\n';
        }
}

const float* AY8910::Amplitude::getEnvVolTable() const
{
        return envVolTable;
}

inline float AY8910::Amplitude::getVolume(unsigned chan) const
{
        assert(!followsEnvelope(chan));
        return vol[chan];
}

inline void AY8910::Amplitude::setChannelVolume(unsigned chan, unsigned value)
{
        envChan[chan] = (value & 0x10) != 0;
        vol[chan] = tables.volume[value & 0x0F];
}

inline bool AY8910::Amplitude::followsEnvelope(unsigned chan) const
{
        return envChan[chan];
}


// Envelope:

// AY8910 and YM2149 behave different here:
//  YM2149 envelope goes twice as fast and has twice as many levels. Here
//  we implement the YM2149 behaviour, but to get the AY8910 behaviour we
//  repeat every level twice in the envVolTable

inline AY8910::Envelope::Envelope(const float* envVolTable_)
{
        envVolTable = envVolTable_;
        period = 1;
        count  = 0;
        step   = 0;
        attack = 0;
        hold      = false;
        alternate = false;
        holding   = false;
}

inline void AY8910::Envelope::reset()
{
        count = 0;
}

inline void AY8910::Envelope::setPeriod(int value)
{
        // twice as fast as AY8910
        //  see also Generator::setPeriod()
        period = std::max(1, 2 * value);
        count = std::min(count, period - 1);
}

inline float AY8910::Envelope::getVolume() const
{
        return envVolTable[step ^ attack];
}

inline void AY8910::Envelope::setShape(unsigned shape)
{
        // do 32 steps for both AY8910 and YM2149
        /*
        envelope shapes:
                C AtAlH
                0 0 x x  \___
                0 1 x x  /___
                1 0 0 0  \\\\
                1 0 0 1  \___
                1 0 1 0  \/\/
                1 0 1 1  \
                1 1 0 0  ////
                1 1 0 1  /
                1 1 1 0  /\/\
                1 1 1 1  /___
        */
        attack = (shape & 0x04) ? 0x1F : 0x00;
        if ((shape & 0x08) == 0) {
                // If Continue = 0, map the shape to the equivalent one
                // which has Continue = 1.
                hold = true;
                alternate = attack != 0;
        } else {
                hold = (shape & 0x01) != 0;
                alternate = (shape & 0x02) != 0;
        }
        count = 0;
        step = 0x1F;
        holding = false;
}

inline bool AY8910::Envelope::isChanging() const
{
        return !holding;
}

inline void AY8910::Envelope::doSteps(int steps)
{
        // For best performance callers should check upfront whether
        //    isChanging() == true
        // Though we can't assert on it because the condition might change
        // in the inner loop(s) of generateChannels().
        //assert(!holding);

        if (holding) return;
        step -= steps;

        // Check current envelope position.
        if (step < 0) {
                if (hold) {
                        if (alternate) attack ^= 0x1F;
                        holding = true;
                        step = 0;
                } else {
                        // If step has looped an odd number of times
                        // (usually 1), invert the output.
                        if (alternate && (step & 0x10)) {
                                attack ^= 0x1F;
                        }
                        step &= 0x1F;
                }
        }
}

inline void AY8910::Envelope::advance(int duration)
{
        assert(count < period);
        count += duration * 2;
        if (count >= period) {
                int steps = count / period;
                count -= steps * period; // equivalent to count %= period;
                doSteps(steps);
        }
}

inline void AY8910::Envelope::doNextEvent()
{
        count = 0;
        doSteps(period == 1 ? 2 : 1);
}

inline unsigned AY8910::Envelope::getNextEventTime() const
{
        assert(count < period);
        return (period - count + 1) / 2;
}

inline void AY8910::Envelope::advanceFast(unsigned duration)
{
        count += 2 * duration;
        assert(count < period);
}



// AY8910 main class:

AY8910::AY8910(const std::string& name_, AY8910Periphery& periphery_,
               const DeviceConfig& config, EmuTime::param time)
        : ResampledSoundDevice(config.getMotherBoard(), name_, "PSG", 3, NATIVE_FREQ_INT, false)
        , periphery(periphery_)
        , debuggable(config.getMotherBoard(), getName())
        , vibratoPercent(
                config.getCommandController(), getName() + "_vibrato_percent",
                "controls strength of vibrato effect", 0.0, 0.0, 10.0)
        , vibratoFrequency(
                config.getCommandController(), getName() + "_vibrato_frequency",
                "frequency of vibrato effect in Hertz", 5, 1.0, 10.0)
        , detunePercent(
                config.getCommandController(), getName() + "_detune_percent",
                "controls strength of detune effect", 0.0, 0.0, 10.0)
        , detuneFrequency(
                config.getCommandController(), getName() + "_detune_frequency",
                "frequency of detune effect in Hertz", 5.0, 1.0, 100.0)
        , directionsCallback(
                config.getGlobalSettings().getInvalidPsgDirectionsSetting())
        , amplitude(config)
        , envelope(amplitude.getEnvVolTable())
        , isAY8910(checkAY8910(config))
        , ignorePortDirections(config.getChildDataAsBool("ignorePortDirections", true))
{
        // (lazily) initialize detune stuff
        detuneInitialized = false;
        update(vibratoPercent);

        // make valgrind happy
        memset(regs, 0, sizeof(regs));

        reset(time);
        registerSound(config);

        // only attach once all initialization is successful
        vibratoPercent.attach(*this);
        detunePercent .attach(*this);
}

AY8910::~AY8910()
{
        vibratoPercent.detach(*this);
        detunePercent .detach(*this);

        unregisterSound();
}

void AY8910::reset(EmuTime::param time)
{
        // Reset generators and envelope.
        for (auto& t : tone) t.reset();
        noise.reset();
        envelope.reset();
        // Reset registers and values derived from them.
        for (unsigned reg = 0; reg <= 15; ++reg) {
                wrtReg(reg, 0, time);
        }
}


byte AY8910::readRegister(unsigned reg, EmuTime::param time)
{
        if (reg >= 16) return 255;
        switch (reg) {
        case AY_PORTA:
                if (!(regs[AY_ENABLE] & PORT_A_DIRECTION)) { // input
                        regs[reg] = periphery.readA(time);
                }
                break;
        case AY_PORTB:
                if (!(regs[AY_ENABLE] & PORT_B_DIRECTION)) { // input
                        regs[reg] = periphery.readB(time);
                }
                break;
        }

        // TODO some AY8910 models have 1F as mask for registers 1, 3, 5
        static constexpr byte regMask[16] = {
                0xff, 0x0f, 0xff, 0x0f, 0xff, 0x0f, 0x1f, 0xff,
                0x1f, 0x1f ,0x1f, 0xff, 0xff, 0x0f, 0xff, 0xff
        };
        return isAY8910 ? regs[reg] & regMask[reg]
                        : regs[reg];
}

byte AY8910::peekRegister(unsigned reg, EmuTime::param time) const
{
        if (reg >= 16) return 255;
        switch (reg) {
        case AY_PORTA:
                if (!(regs[AY_ENABLE] & PORT_A_DIRECTION)) { // input
                        return periphery.readA(time);
                }
                break;
        case AY_PORTB:
                if (!(regs[AY_ENABLE] & PORT_B_DIRECTION)) { // input
                        return periphery.readB(time);
                }
                break;
        }
        return regs[reg];
}


void AY8910::writeRegister(unsigned reg, byte value, EmuTime::param time)
{
        if (reg >= 16) return;
        if ((reg < AY_PORTA) && (reg == AY_ESHAPE || regs[reg] != value)) {
                // Update the output buffer before changing the register.
                updateStream(time);
        }
        wrtReg(reg, value, time);
}
void AY8910::wrtReg(unsigned reg, byte value, EmuTime::param time)
{
        // Warn/force port directions
        if (reg == AY_ENABLE) {
                if (value & PORT_A_DIRECTION) {
                        directionsCallback.execute();
                }
                if (ignorePortDirections)
                {
                        // portA -> input
                        // portB -> output
                        value = (value & ~PORT_A_DIRECTION) | PORT_B_DIRECTION;
                }
        }

        // Note: unused bits are stored as well; they can be read back.
        byte diff = regs[reg] ^ value;
        regs[reg] = value;

        switch (reg) {
        case AY_AFINE:
        case AY_ACOARSE:
        case AY_BFINE:
        case AY_BCOARSE:
        case AY_CFINE:
        case AY_CCOARSE:
                tone[reg / 2].setPeriod(regs[reg & ~1] + 256 * (regs[reg | 1] & 0x0F));
                break;
        case AY_NOISEPER:
                // half the frequency of tone generation
                noise.setPeriod(2 * (value & 0x1F));
                break;
        case AY_AVOL:
        case AY_BVOL:
        case AY_CVOL:
                amplitude.setChannelVolume(reg - AY_AVOL, value);
                break;
        case AY_EFINE:
        case AY_ECOARSE:
                // also half the frequency of tone generation, but handled
                // inside Envelope::setPeriod()
                envelope.setPeriod(regs[AY_EFINE] + 256 * regs[AY_ECOARSE]);
                break;
        case AY_ESHAPE:
                envelope.setShape(value);
                break;
        case AY_ENABLE:
                if (diff & PORT_A_DIRECTION) {
                        // port A changed
                        if (value & PORT_A_DIRECTION) {
                                // from input to output
                                periphery.writeA(regs[AY_PORTA], time);
                        } else {
                                // from output to input
                                periphery.writeA(0xff, time);
                        }
                }
                if (diff & PORT_B_DIRECTION) {
                        // port B changed
                        if (value & PORT_B_DIRECTION) {
                                // from input to output
                                periphery.writeB(regs[AY_PORTB], time);
                        } else {
                                // from output to input
                                periphery.writeB(0xff, time);
                        }
                }
                break;
        case AY_PORTA:
                if (regs[AY_ENABLE] & PORT_A_DIRECTION) { // output
                        periphery.writeA(value, time);
                }
                break;
        case AY_PORTB:
                if (regs[AY_ENABLE] & PORT_B_DIRECTION) { // output
                        periphery.writeB(value, time);
                }
                break;
        }
}

void AY8910::generateChannels(float** bufs, unsigned num)
{
        // Disable channels with volume 0: since the sample value doesn't matter,
        // we can use the fastest path.
        unsigned chanEnable = regs[AY_ENABLE];
        for (unsigned chan = 0; chan < 3; ++chan) {
                if ((!amplitude.followsEnvelope(chan) &&
                     (amplitude.getVolume(chan) == 0.0f)) ||
                    (amplitude.followsEnvelope(chan) &&
                     !envelope.isChanging() &&
                     (envelope.getVolume() == 0.0f))) {
                        bufs[chan] = nullptr;
                        tone[chan].advance(num);
                        chanEnable |= 0x09 << chan;
                }
        }
        // Noise disabled on all channels?
        if ((chanEnable & 0x38) == 0x38) {
                noise.advance(num);
        }

        // Calculate samples.
        // The 8910 has three outputs, each output is the mix of one of the
        // three tone generators and of the (single) noise generator. The two
        // are mixed BEFORE going into the DAC. The formula to mix each channel
        // is:
        //   (ToneOn | ToneDisable) & (NoiseOn | NoiseDisable),
        //   where ToneOn and NoiseOn are the current generator state
        //   and ToneDisable and NoiseDisable come from the enable reg.
        // Note that this means that if both tone and noise are disabled, the
        // output is 1, not 0, and can be modulated by changing the volume.
        bool envelopeUpdated = false;
        Envelope initialEnvelope = envelope;
        NoiseGenerator initialNoise = noise;
        for (unsigned chan = 0; chan < 3; ++chan, chanEnable >>= 1) {
                auto* buf = bufs[chan];
                if (!buf) continue;
                ToneGenerator& t = tone[chan];
                if (envelope.isChanging() && amplitude.followsEnvelope(chan)) {
                        envelopeUpdated = true;
                        envelope = initialEnvelope;
                        if ((chanEnable & 0x09) == 0x08) {
                                // no noise, square wave: alternating between 0 and 1.
                                auto val = t.getOutput() * envelope.getVolume();
                                unsigned remaining = num;
                                unsigned nextE = envelope.getNextEventTime();
                                unsigned nextT = t.getNextEventTime();
                                while ((nextT <= remaining) || (nextE <= remaining)) {
                                        if (nextT < nextE) {
                                                addFill(buf, val, nextT);
                                                remaining -= nextT;
                                                nextE -= nextT;
                                                envelope.advanceFast(nextT);
                                                t.doNextEvent(*this);
                                                nextT = t.getNextEventTime();
                                        } else if (nextE < nextT) {
                                                addFill(buf, val, nextE);
                                                remaining -= nextE;
                                                nextT -= nextE;
                                                t.advanceFast(nextE);
                                                envelope.doNextEvent();
                                                nextE = envelope.getNextEventTime();
                                        } else {
                                                assert(nextT == nextE);
                                                addFill(buf, val, nextT);
                                                remaining -= nextT;
                                                t.doNextEvent(*this);
                                                nextT = t.getNextEventTime();
                                                envelope.doNextEvent();
                                                nextE = envelope.getNextEventTime();
                                        }
                                        val = t.getOutput() * envelope.getVolume();
                                }
                                if (remaining) {
                                        // last interval (without events)
                                        addFill(buf, val, remaining);
                                        t.advanceFast(remaining);
                                        envelope.advanceFast(remaining);
                                }

                        } else if ((chanEnable & 0x09) == 0x09) {
                                // no noise, channel disabled: always 1.
                                auto val = envelope.getVolume();
                                unsigned remaining = num;
                                unsigned next = envelope.getNextEventTime();
                                while (next <= remaining) {
                                        addFill(buf, val, next);
                                        remaining -= next;
                                        envelope.doNextEvent();
                                        val = envelope.getVolume();
                                        next = envelope.getNextEventTime();
                                }
                                if (remaining) {
                                        // last interval (without events)
                                        addFill(buf, val, remaining);
                                        envelope.advanceFast(remaining);
                                }
                                t.advance(num);

                        } else if ((chanEnable & 0x09) == 0x00) {
                                // noise enabled, tone enabled
                                noise = initialNoise;
                                auto val = noise.getOutput() * t.getOutput() * envelope.getVolume();
                                unsigned remaining = num;
                                unsigned nextT = t.getNextEventTime();
                                unsigned nextN = noise.getNextEventTime();
                                unsigned nextE = envelope.getNextEventTime();
                                unsigned next = std::min(std::min(nextT, nextN), nextE);
                                while (next <= remaining) {
                                        addFill(buf, val, next);
                                        remaining -= next;
                                        nextT -= next;
                                        nextN -= next;
                                        nextE -= next;
                                        if (nextT) {
                                                t.advanceFast(next);
                                        } else {
                                                t.doNextEvent(*this);
                                                nextT = t.getNextEventTime();
                                        }
                                        if (nextN) {
                                                noise.advanceFast(next);
                                        } else {
                                                noise.doNextEvent();
                                                nextN = noise.getNextEventTime();
                                        }
                                        if (nextE) {
                                                envelope.advanceFast(next);
                                        } else {
                                                envelope.doNextEvent();
                                                nextE = envelope.getNextEventTime();
                                        }
                                        next = std::min(std::min(nextT, nextN), nextE);
                                        val = noise.getOutput() * t.getOutput() * envelope.getVolume();
                                }
                                if (remaining) {
                                        // last interval (without events)
                                        addFill(buf, val, remaining);
                                        t.advanceFast(remaining);
                                        noise.advanceFast(remaining);
                                        envelope.advanceFast(remaining);
                                }

                        } else {
                                // noise enabled, tone disabled
                                noise = initialNoise;
                                auto val = noise.getOutput() * envelope.getVolume();
                                unsigned remaining = num;
                                unsigned nextE = envelope.getNextEventTime();
                                unsigned nextN = noise.getNextEventTime();
                                while ((nextN <= remaining) || (nextE <= remaining)) {
                                        if (nextN < nextE) {
                                                addFill(buf, val, nextN);
                                                remaining -= nextN;
                                                nextE -= nextN;
                                                envelope.advanceFast(nextN);
                                                noise.doNextEvent();
                                                nextN = noise.getNextEventTime();
                                        } else if (nextE < nextN) {
                                                addFill(buf, val, nextE);
                                                remaining -= nextE;
                                                nextN -= nextE;
                                                noise.advanceFast(nextE);
                                                envelope.doNextEvent();
                                                nextE = envelope.getNextEventTime();
                                        } else {
                                                assert(nextN == nextE);
                                                addFill(buf, val, nextN);
                                                remaining -= nextN;
                                                noise.doNextEvent();
                                                nextN = noise.getNextEventTime();
                                                envelope.doNextEvent();
                                                nextE = envelope.getNextEventTime();
                                        }
                                        val = noise.getOutput() * envelope.getVolume();
                                }
                                if (remaining) {
                                        // last interval (without events)
                                        addFill(buf, val, remaining);
                                        noise.advanceFast(remaining);
                                        envelope.advanceFast(remaining);
                                }
                                t.advance(num);
                        }
                } else {
                        // no (changing) envelope on this channel
                        auto volume = amplitude.followsEnvelope(chan)
                                    ? envelope.getVolume()
                                    : amplitude.getVolume(chan);
                        if ((chanEnable & 0x09) == 0x08) {
                                // no noise, square wave: alternating between 0 and 1.
                                auto val = t.getOutput() * volume;
                                unsigned remaining = num;
                                unsigned next = t.getNextEventTime();
                                while (next <= remaining) {
                                        addFill(buf, val, next);
                                        val = volume - val;
                                        remaining -= next;
                                        t.doNextEvent(*this);
                                        next = t.getNextEventTime();
                                }
                                if (remaining) {
                                        // last interval (without events)
                                        addFill(buf, val, remaining);
                                        t.advanceFast(remaining);
                                }

                        } else if ((chanEnable & 0x09) == 0x09) {
                                // no noise, channel disabled: always 1.
                                addFill(buf, volume, num);
                                t.advance(num);

                        } else if ((chanEnable & 0x09) == 0x00) {
                                // noise enabled, tone enabled
                                noise = initialNoise;
                                auto val1 = t.getOutput() * volume;
                                auto val2 = val1 * noise.getOutput();
                                unsigned remaining = num;
                                unsigned nextN = noise.getNextEventTime();
                                unsigned nextT = t.getNextEventTime();
                                while ((nextN <= remaining) || (nextT <= remaining)) {
                                        if (nextT < nextN) {
                                                addFill(buf, val2, nextT);
                                                remaining -= nextT;
                                                nextN -= nextT;
                                                noise.advanceFast(nextT);
                                                t.doNextEvent(*this);
                                                nextT = t.getNextEventTime();
                                                val1 = volume - val1;
                                                val2 = val1 * noise.getOutput();
                                        } else if (nextN < nextT) {
                                                addFill(buf, val2, nextN);
                                                remaining -= nextN;
                                                nextT -= nextN;
                                                t.advanceFast(nextN);
                                                noise.doNextEvent();
                                                nextN = noise.getNextEventTime();
                                                val2 = val1 * noise.getOutput();
                                        } else {
                                                assert(nextT == nextN);
                                                addFill(buf, val2, nextT);
                                                remaining -= nextT;
                                                t.doNextEvent(*this);
                                                nextT = t.getNextEventTime();
                                                noise.doNextEvent();
                                                nextN = noise.getNextEventTime();
                                                val1 = volume - val1;
                                                val2 = val1 * noise.getOutput();
                                        }
                                }
                                if (remaining) {
                                        // last interval (without events)
                                        addFill(buf, val2, remaining);
                                        t.advanceFast(remaining);
                                        noise.advanceFast(remaining);
                                }

                        } else {
                                // noise enabled, tone disabled
                                noise = initialNoise;
                                unsigned remaining = num;
                                auto val = noise.getOutput() * volume;
                                unsigned next = noise.getNextEventTime();
                                while (next <= remaining) {
                                        addFill(buf, val, next);
                                        remaining -= next;
                                        noise.doNextEvent();
                                        val = noise.getOutput() * volume;
                                        next = noise.getNextEventTime();
                                }
                                if (remaining) {
                                        // last interval (without events)
                                        addFill(buf, val, remaining);
                                        noise.advanceFast(remaining);
                                }
                                t.advance(num);
                        }
                }
        }

        // Envelope not yet updated?
        if (envelope.isChanging() && !envelopeUpdated) {
                envelope.advance(num);
        }
}

float AY8910::getAmplificationFactorImpl() const
{
        return 1.0f;
}

void AY8910::update(const Setting& setting)
{
        if ((&setting == &vibratoPercent) ||
            (&setting == &detunePercent)) {
                doDetune = (vibratoPercent.getDouble() != 0) ||
                           (detunePercent .getDouble() != 0);
                if (doDetune && !detuneInitialized) {
                        detuneInitialized = true;
                        initDetune();
                }
        } else {
                ResampledSoundDevice::update(setting);
        }
}


// Debuggable

AY8910::Debuggable::Debuggable(MSXMotherBoard& motherBoard_, const string& name_)
        : SimpleDebuggable(motherBoard_, name_ + " regs", "PSG", 0x10)
{
}

byte AY8910::Debuggable::read(unsigned address, EmuTime::param time)
{
        auto& ay8910 = OUTER(AY8910, debuggable);
        return ay8910.readRegister(address, time);
}

void AY8910::Debuggable::write(unsigned address, byte value, EmuTime::param time)
{
        auto& ay8910 = OUTER(AY8910, debuggable);
        return ay8910.writeRegister(address, value, time);
}


template<typename Archive>
void AY8910::serialize(Archive& ar, unsigned /*version*/)
{
        ar.serialize("toneGenerators", tone,
                     "noiseGenerator", noise,
                     "envelope",       envelope,
                     "registers",      regs);

        // amplitude
        if (ar.isLoader()) {
                for (int i = 0; i < 3; ++i) {
                        amplitude.setChannelVolume(i, regs[i + AY_AVOL]);
                }
        }
}
INSTANTIATE_SERIALIZE_METHODS(AY8910);

// version 1: initial version
// version 2: removed 'output' member variable
template<typename Archive>
void AY8910::Generator::serialize(Archive& ar, unsigned /*version*/)
{
        ar.serialize("period", period,
                     "count", count);
}
INSTANTIATE_SERIALIZE_METHODS(AY8910::Generator);

// version 1: initial version
// version 2: moved 'output' variable from base class to here
template<typename Archive>
void AY8910::ToneGenerator::serialize(Archive& ar, unsigned version)
{
        ar.template serializeInlinedBase<Generator>(*this, version);
        ar.serialize("vibratoCount", vibratoCount,
                     "detuneCount", detuneCount);
        if (ar.versionAtLeast(version, 2)) {
                ar.serialize("output", output);
        } else {
                // don't bother trying to restore this from the old location:
                // it doesn't influence any MSX-observable state, and the
                // difference in generated sound will likely be inaudible
        }
}
INSTANTIATE_SERIALIZE_METHODS(AY8910::ToneGenerator);

// version 1: initial version
// version 2: removed 'output' variable from base class, not stored here but
//            instead it's calculated from 'random' when needed
template<typename Archive>
void AY8910::NoiseGenerator::serialize(Archive& ar, unsigned version)
{
        ar.template serializeInlinedBase<Generator>(*this, version);
        ar.serialize("random", random);
}
INSTANTIATE_SERIALIZE_METHODS(AY8910::NoiseGenerator);

template<typename Archive>
void AY8910::Envelope::serialize(Archive& ar, unsigned /*version*/)
{
        ar.serialize("period",    period,
                     "count",     count,
                     "step",      step,
                     "attack",    attack,
                     "hold",      hold,
                     "alternate", alternate,
                     "holding",   holding);
}
INSTANTIATE_SERIALIZE_METHODS(AY8910::Envelope);

} // namespace openmsx