MSXMixer.cc

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#include "MSXMixer.hh"
#include "Mixer.hh"
#include "SoundDevice.hh"
#include "MSXMotherBoard.hh"
#include "MSXCommandController.hh"
#include "TclObject.hh"
#include "ThrottleManager.hh"
#include "GlobalSettings.hh"
#include "IntegerSetting.hh"
#include "StringSetting.hh"
#include "BooleanSetting.hh"
#include "CommandException.hh"
#include "AviRecorder.hh"
#include "Filename.hh"
#include "CliComm.hh"
#include "stl.hh"
#include "aligned.hh"
#include "outer.hh"
#include "ranges.hh"
#include "unreachable.hh"
#include "view.hh"
#include "vla.hh"
#include <cassert>
#include <cmath>
#include <cstring>
#include <memory>
#include <tuple>

#ifdef __SSE2__
#include "emmintrin.h"
#endif

using std::string;
using std::vector;

namespace openmsx {

MSXMixer::MSXMixer(Mixer& mixer_, MSXMotherBoard& motherBoard_,
                   GlobalSettings& globalSettings)
        : Schedulable(motherBoard_.getScheduler())
        , mixer(mixer_)
        , motherBoard(motherBoard_)
        , commandController(motherBoard.getMSXCommandController())
        , masterVolume(mixer.getMasterVolume())
        , speedSetting(globalSettings.getSpeedSetting())
        , throttleManager(globalSettings.getThrottleManager())
        , prevTime(getCurrentTime(), 44100)
        , soundDeviceInfo(commandController.getMachineInfoCommand())
        , recorder(nullptr)
        , synchronousCounter(0)
{
        hostSampleRate = 44100;
        fragmentSize = 0;

        muteCount = 1;
        unmute(); // calls Mixer::registerMixer()

        reschedule2();

        masterVolume.attach(*this);
        speedSetting.attach(*this);
        throttleManager.attach(*this);
}

MSXMixer::~MSXMixer()
{
        if (recorder) {
                recorder->stop();
        }
        assert(infos.empty());

        throttleManager.detach(*this);
        speedSetting.detach(*this);
        masterVolume.detach(*this);

        mute(); // calls Mixer::unregisterMixer()
}

void MSXMixer::registerSound(SoundDevice& device, float volume,
                             int balance, unsigned numChannels)
{
        // TODO read volume/balance(mode) from config file
        const string& name = device.getName();
        SoundDeviceInfo info;
        info.device = &device;
        info.defaultVolume = volume;
        info.volumeSetting = std::make_unique<IntegerSetting>(
                commandController, name + "_volume",
                "the volume of this sound chip", 75, 0, 100);
        info.balanceSetting = std::make_unique<IntegerSetting>(
                commandController, name + "_balance",
                "the balance of this sound chip", balance, -100, 100);

        info.volumeSetting->attach(*this);
        info.balanceSetting->attach(*this);

        for (unsigned i = 0; i < numChannels; ++i) {
                SoundDeviceInfo::ChannelSettings channelSettings;
                string ch_name = strCat(name, "_ch", i + 1);

                channelSettings.recordSetting = std::make_unique<StringSetting>(
                        commandController, ch_name + "_record",
                        "filename to record this channel to",
                        std::string_view{}, Setting::DONT_SAVE);
                channelSettings.recordSetting->attach(*this);

                channelSettings.muteSetting = std::make_unique<BooleanSetting>(
                        commandController, ch_name + "_mute",
                        "sets mute-status of individual sound channels",
                        false, Setting::DONT_SAVE);
                channelSettings.muteSetting->attach(*this);

                info.channelSettings.push_back(std::move(channelSettings));
        }

        device.setOutputRate(getSampleRate());
        auto& i = infos.emplace_back(std::move(info));
        updateVolumeParams(i);

        commandController.getCliComm().update(CliComm::SOUNDDEVICE, device.getName(), "add");
}

void MSXMixer::unregisterSound(SoundDevice& device)
{
        auto it = rfind_if_unguarded(infos,
                [&](const SoundDeviceInfo& i) { return i.device == &device; });
        it->volumeSetting->detach(*this);
        it->balanceSetting->detach(*this);
        for (auto& s : it->channelSettings) {
                s.recordSetting->detach(*this);
                s.muteSetting->detach(*this);
        }
        move_pop_back(infos, it);
        commandController.getCliComm().update(CliComm::SOUNDDEVICE, device.getName(), "remove");
}

void MSXMixer::setSynchronousMode(bool synchronous)
{
        // TODO ATM synchronous is not used anymore
        if (synchronous) {
                ++synchronousCounter;
                if (synchronousCounter == 1) {
                        setMixerParams(fragmentSize, hostSampleRate);
                }
        } else {
                assert(synchronousCounter > 0);
                --synchronousCounter;
                if (synchronousCounter == 0) {
                        setMixerParams(fragmentSize, hostSampleRate);
                }
        }
}

double MSXMixer::getEffectiveSpeed() const
{
        return synchronousCounter
             ? 1.0
             : speedSetting.getInt() / 100.0;
}

void MSXMixer::updateStream(EmuTime::param time)
{
        union {
                float mixBuffer[8192 * 2]; // make sure buffer is 32-bit aligned
#ifdef __SSE2__
                __m128i dummy2; // and optionally also 128-bit
#endif
        };

        unsigned count = prevTime.getTicksTill(time);
        assert(count <= 8192);

        // call generate() even if count==0 and even if muted
        generate(mixBuffer, time, count);

        if (!muteCount && fragmentSize) {
                mixer.uploadBuffer(*this, mixBuffer, count);
        }

        if (recorder) {
                recorder->addWave(count, mixBuffer);
        }

        prevTime += count;
}


// Various (inner) loops that multiply one buffer by a constant and add the
// result to a second buffer. Either buffer can be mono or stereo, so if
// necessary the mono buffer is expanded to stereo. It's possible the
// accumulation buffer is still empty (as-if it contains zeros), in that case
// we skip the accumulation step.

// buf[0:n] *= f
static inline void mul(float* buf, int n, float f)
{
        // C++ version, unrolled 4x,
        //   this allows gcc/clang to do much better auto-vectorization
        // Note that this can process upto 3 samples too many, but that's OK.
        assume_SSE_aligned(buf);
        int i = 0;
        do {
                buf[i + 0] *= f;
                buf[i + 1] *= f;
                buf[i + 2] *= f;
                buf[i + 3] *= f;
                i += 4;
        } while (i < n);
}

// acc[0:n] += mul[0:n] * f
static inline void mulAcc(
        float* __restrict acc, const float* __restrict mul, int n, float f)
{
        // C++ version, unrolled 4x, see comments above.
        assume_SSE_aligned(acc);
        assume_SSE_aligned(mul);
        int i = 0;
        do {
                acc[i + 0] += mul[i + 0] * f;
                acc[i + 1] += mul[i + 1] * f;
                acc[i + 2] += mul[i + 2] * f;
                acc[i + 3] += mul[i + 3] * f;
                i += 4;
        } while (i < n);
}

// buf[0:2n+0:2] = buf[0:n] * l
// buf[1:2n+1:2] = buf[0:n] * r
static inline void mulExpand(float* buf, int n, float l, float r)
{
        int i = n;
        do {
                --i; // back-to-front
                auto t = buf[i];
                buf[2 * i + 0] = l * t;
                buf[2 * i + 1] = r * t;
        } while (i != 0);
}

// acc[0:2n+0:2] += mul[0:n] * l
// acc[1:2n+1:2] += mul[0:n] * r
static inline void mulExpandAcc(
        float* __restrict acc, const float* __restrict mul, int n,
        float l, float r)
{
        int i = 0;
        do {
                auto t = mul[i];
                acc[2 * i + 0] += l * t;
                acc[2 * i + 1] += r * t;
        } while (++i < n);
}

// buf[0:2n+0:2] = buf[0:2n+0:2] * l1 + buf[1:2n+1:2] * l2
// buf[1:2n+1:2] = buf[0:2n+0:2] * r1 + buf[1:2n+1:2] * r2
static inline void mulMix2(float* buf, int n, float l1, float l2, float r1, float r2)
{
        int i = 0;
        do {
                auto t1 = buf[2 * i + 0];
                auto t2 = buf[2 * i + 1];
                buf[2 * i + 0] = l1 * t1 + l2 * t2;
                buf[2 * i + 1] = r1 * t1 + r2 * t2;
        } while (++i < n);
}

// acc[0:2n+0:2] += mul[0:2n+0:2] * l1 + mul[1:2n+1:2] * l2
// acc[1:2n+1:2] += mul[0:2n+0:2] * r1 + mul[1:2n+1:2] * r2
static inline void mulMix2Acc(
        float* __restrict acc, const float* __restrict mul, int n,
        float l1, float l2, float r1, float r2)
{
        int i = 0;
        do {
                auto t1 = mul[2 * i + 0];
                auto t2 = mul[2 * i + 1];
                acc[2 * i + 0] += l1 * t1 + l2 * t2;
                acc[2 * i + 1] += r1 * t1 + r2 * t2;
        } while (++i < n);
}


// DC removal filter routines:
//
//  formula:
//     y(n) = x(n) - x(n-1) + R * y(n-1)
//  implemented as:
//     t1 = R * t0 + x(n)    mathematically equivalent, has
//     y(n) = t1 - t0        the same number of operations but
//     t0 = t1               requires only one state variable
//    see: http://en.wikipedia.org/wiki/Digital_filter#Direct_Form_I
//  with:
//     R = 1 - (2*pi * cut-off-frequency / samplerate)
//  we take R = 511/512
//   44100Hz --> cutt-off freq = 14Hz
//   22050Hz                     7Hz
constexpr auto R = 511.0f / 512.0f;

// No new input, previous output was (non-zero) mono.
static inline float filterMonoNull(float t0, float* __restrict out, int n)
{
        assert(n > 0);
        int i = 0;
        do {
                auto t1 = R * t0;
                auto s = t1 - t0;
                out[2 * i + 0] = s;
                out[2 * i + 1] = s;
                t0 = t1;
        } while (++i < n);
        return t0;
}

// No new input, previous output was (non-zero) stereo.
static inline std::tuple<float, float> filterStereoNull(
        float tl0, float tr0, float* __restrict out, int n)
{
        assert(n > 0);
        int i = 0;
        do {
                float tl1 = R * tl0;
                float tr1 = R * tr0;
                out[2 * i + 0] = tl1 - tl0;
                out[2 * i + 1] = tr1 - tr0;
                tl0 = tl1;
                tr0 = tr1;
        } while (++i < n);
        return std::tuple(tl0, tr0);
}

// New input is mono, previous output was also mono.
static inline float filterMonoMono(float t0, const float* __restrict in,
                                   float* __restrict out, int n)
{
        assert(n > 0);
        int i = 0;
        do {
                auto t1 = R * t0 + in[i];
                auto s = t1 - t0;
                out[2 * i + 0] = s;
                out[2 * i + 1] = s;
                t0 = t1;
        } while (++i < n);
        return t0;
}

// New input is mono, previous output was stereo
static inline std::tuple<float, float>
filterStereoMono(float tl0, float tr0, const float* __restrict in,
                 float* __restrict out, int n)
{
        assert(n > 0);
        int i = 0;
        do {
                auto x = in[i];
                auto tl1 = R * tl0 + x;
                auto tr1 = R * tr0 + x;
                out[2 * i + 0] = tl1 - tl0;
                out[2 * i + 1] = tr1 - tr0;
                tl0 = tl1;
                tr0 = tr1;
        } while (++i < n);
        return std::tuple(tl0, tr0);
}

// New input is stereo, (previous output either mono/stereo)
static inline std::tuple<float, float>
filterStereoStereo(float tl0, float tr0, const float* __restrict in,
                   float* __restrict out, int n)
{
        assert(n > 0);
        int i = 0;
        do {
                auto tl1 = R * tl0 + in[2 * i + 0];
                auto tr1 = R * tr0 + in[2 * i + 1];
                out[2 * i + 0] = tl1 - tl0;
                out[2 * i + 1] = tr1 - tr0;
                tl0 = tl1;
                tr0 = tr1;
        } while (++i < n);
        return std::tuple(tl0, tr0);
}

// We have both mono and stereo input (and produce stereo output)
static inline std::tuple<float, float>
filterBothStereo(float tl0, float tr0, const float* __restrict inM,
                 const float* __restrict inS, float* __restrict out, int n)
{
        assert(n > 0);
        int i = 0;
        do {
                auto m = inM[i];
                auto tl1 = R * tl0 + inS[2 * i + 0] + m;
                auto tr1 = R * tr0 + inS[2 * i + 1] + m;
                out[2 * i + 0] = tl1 - tl0;
                out[2 * i + 1] = tr1 - tr0;
                tl0 = tl1;
                tr0 = tr1;
        } while (++i < n);
        return std::tuple(tl0, tr0);
}

static bool approxEqual(float x, float y)
{
        constexpr float threshold = 1.0f / 32768;
        return std::abs(x - y) < threshold;
}

void MSXMixer::generate(float* output, EmuTime::param time, unsigned samples)
{
        // The code below is specialized for a lot of cases (before this
        // routine was _much_ shorter). This is done because this routine
        // ends up relatively high (top 5) in a profile run.
        // After these specialization this routine runs about two times
        // faster for the common cases (mono output or no sound at all).
        // In total emulation time this gave a speedup of about 2%.

        // When samples==0, call updateBuffer() but skip all further processing
        // (handling this as a special case allows to simplify the code below).
        if (samples == 0) {
                alignas(SSE_ALIGNMENT) float dummyBuf[4];
                for (auto& info : infos) {
                        info.device->updateBuffer(0, dummyBuf, time);
                }
                return;
        }

        // +3 to allow processing samples in groups of 4 (and upto 3 samples
        // more than requested).
        VLA_SSE_ALIGNED(float, monoBuf,       samples + 3);
        VLA_SSE_ALIGNED(float, stereoBuf, 2 * samples + 3);
        VLA_SSE_ALIGNED(float, tmpBuf,    2 * samples + 3);

        constexpr unsigned HAS_MONO_FLAG = 1;
        constexpr unsigned HAS_STEREO_FLAG = 2;
        unsigned usedBuffers = 0;

        // FIXME: The Infos should be ordered such that all the mono
        // devices are handled first
        for (auto& info : infos) {
                SoundDevice& device = *info.device;
                auto l1 = info.left1;
                auto r1 = info.right1;
                if (!device.isStereo()) {
                        if (l1 == r1) {
                                if (!(usedBuffers & HAS_MONO_FLAG)) {
                                        if (device.updateBuffer(samples, monoBuf, time)) {
                                                usedBuffers |= HAS_MONO_FLAG;
                                                mul(monoBuf, samples, l1);
                                        }
                                } else {
                                        if (device.updateBuffer(samples, tmpBuf, time)) {
                                                mulAcc(monoBuf, tmpBuf, samples, l1);
                                        }
                                }
                        } else {
                                if (!(usedBuffers & HAS_STEREO_FLAG)) {
                                        if (device.updateBuffer(samples, stereoBuf, time)) {
                                                usedBuffers |= HAS_STEREO_FLAG;
                                                mulExpand(stereoBuf, samples, l1, r1);
                                        }
                                } else {
                                        if (device.updateBuffer(samples, tmpBuf, time)) {
                                                mulExpandAcc(stereoBuf, tmpBuf, samples, l1, r1);
                                        }
                                }
                        }
                } else {
                        auto l2 = info.left2;
                        auto r2 = info.right2;
                        if (l1 == r2) {
                                assert(l2 == 0.0f);
                                assert(r1 == 0.0f);
                                if (!(usedBuffers & HAS_STEREO_FLAG)) {
                                        if (device.updateBuffer(samples, stereoBuf, time)) {
                                                usedBuffers |= HAS_STEREO_FLAG;
                                                mul(stereoBuf, 2 * samples, l1);
                                        }
                                } else {
                                        if (device.updateBuffer(samples, tmpBuf, time)) {
                                                mulAcc(stereoBuf, tmpBuf, 2 * samples, l1);
                                        }
                                }
                        } else {
                                if (!(usedBuffers & HAS_STEREO_FLAG)) {
                                        if (device.updateBuffer(samples, stereoBuf, time)) {
                                                usedBuffers |= HAS_STEREO_FLAG;
                                                mulMix2(stereoBuf, samples, l1, l2, r1, r2);
                                        }
                                } else {
                                        if (device.updateBuffer(samples, tmpBuf, time)) {
                                                mulMix2Acc(stereoBuf, tmpBuf, samples, l1, l2, r1, r2);
                                        }
                                }
                        }
                }
        }

        // DC removal filter
        switch (usedBuffers) {
        case 0: // no new input
                if (approxEqual(tl0, tr0)) {
                        if (approxEqual(tl0, 0.0f)) {
                                // Output was zero, new input is zero,
                                // after DC-filter output will still be zero.
                                memset(output, 0, 2 * samples * sizeof(float));
                                tl0 = tr0 = 0.0f;
                        } else {
                                // Output was not zero, but it was the same left and right.
                                tl0 = filterMonoNull(tl0, output, samples);
                                tr0 = tl0;
                        }
                } else {
                        std::tie(tl0, tr0) = filterStereoNull(tl0, tr0, output, samples);
                }
                break;

        case HAS_MONO_FLAG: // only mono
                if (approxEqual(tl0, tr0)) {
                        // previous output was also mono
                        tl0 = filterMonoMono(tl0, monoBuf, output, samples);
                        tr0 = tl0;
                } else {
                        // previous output was stereo, rarely triggers but needed for correctness
                        std::tie(tl0, tr0) = filterStereoMono(tl0, tr0, monoBuf, output, samples);
                }
                break;

        case HAS_STEREO_FLAG: // only stereo
                std::tie(tl0, tr0) = filterStereoStereo(tl0, tr0, stereoBuf, output, samples);
                break;

        default: // mono + stereo
                std::tie(tl0, tr0) = filterBothStereo(tl0, tr0, monoBuf, stereoBuf, output, samples);
        }
}

bool MSXMixer::needStereoRecording() const
{
        return ranges::any_of(infos, [](auto& info) {
                return info.device->isStereo() ||
                       info.balanceSetting->getInt() != 0;
        });
}

void MSXMixer::mute()
{
        if (muteCount == 0) {
                mixer.unregisterMixer(*this);
        }
        ++muteCount;
}

void MSXMixer::unmute()
{
        --muteCount;
        if (muteCount == 0) {
                tl0 = tr0 = 0.0f;
                mixer.registerMixer(*this);
        }
}

void MSXMixer::reInit()
{
        prevTime.reset(getCurrentTime());
        prevTime.setFreq(hostSampleRate / getEffectiveSpeed());
        reschedule();
}
void MSXMixer::reschedule()
{
        removeSyncPoints();
        reschedule2();
}
void MSXMixer::reschedule2()
{
        unsigned size = (!muteCount && fragmentSize) ? fragmentSize : 512;
        setSyncPoint(prevTime.getFastAdd(size));
}

void MSXMixer::setMixerParams(unsigned newFragmentSize, unsigned newSampleRate)
{
        // TODO old code checked that values did actually change,
        //      investigate if this optimization is worth it
        hostSampleRate = newSampleRate;
        fragmentSize = newFragmentSize;

        reInit(); // must come before call to setOutputRate()

        for (auto& info : infos) {
                info.device->setOutputRate(newSampleRate);
        }
}

void MSXMixer::setRecorder(AviRecorder* newRecorder)
{
        if ((recorder != nullptr) != (newRecorder != nullptr)) {
                setSynchronousMode(newRecorder != nullptr);
        }
        recorder = newRecorder;
}

void MSXMixer::update(const Setting& setting)
{
        if (&setting == &masterVolume) {
                updateMasterVolume();
        } else if (&setting == &speedSetting) {
                if (synchronousCounter == 0) {
                        setMixerParams(fragmentSize, hostSampleRate);
                } else {
                        // Avoid calling reInit() while recording because
                        // each call causes a small hiccup in the sound (and
                        // while recording this call anyway has no effect).
                        // This was noticable while sliding the speed slider
                        // in catapult (becuase this causes many changes in
                        // the speed setting).
                }
        } else if (dynamic_cast<const IntegerSetting*>(&setting)) {
                auto it = find_if_unguarded(infos,
                        [&](const SoundDeviceInfo& i) {
                                return (i.volumeSetting .get() == &setting) ||
                                       (i.balanceSetting.get() == &setting); });
                updateVolumeParams(*it);
        } else if (dynamic_cast<const StringSetting*>(&setting)) {
                changeRecordSetting(setting);
        } else if (dynamic_cast<const BooleanSetting*>(&setting)) {
                changeMuteSetting(setting);
        } else {
                UNREACHABLE;
        }
}

void MSXMixer::changeRecordSetting(const Setting& setting)
{
        for (auto& info : infos) {
                unsigned channel = 0;
                for (auto& s : info.channelSettings) {
                        if (s.recordSetting.get() == &setting) {
                                info.device->recordChannel(
                                        channel,
                                        Filename(string(s.recordSetting->getString())));
                                return;
                        }
                        ++channel;
                }
        }
        UNREACHABLE;
}

void MSXMixer::changeMuteSetting(const Setting& setting)
{
        for (auto& info : infos) {
                unsigned channel = 0;
                for (auto& s : info.channelSettings) {
                        if (s.muteSetting.get() == &setting) {
                                info.device->muteChannel(
                                        channel, s.muteSetting->getBoolean());
                                return;
                        }
                        ++channel;
                }
        }
        UNREACHABLE;
}

void MSXMixer::update(const ThrottleManager& /*throttleManager*/)
{
        //reInit();
        // TODO Should this be removed?
}

void MSXMixer::updateVolumeParams(SoundDeviceInfo& info)
{
        int mVolume = masterVolume.getInt();
        int dVolume = info.volumeSetting->getInt();
        float volume = info.defaultVolume * mVolume * dVolume / (100.0f * 100.0f);
        int balance = info.balanceSetting->getInt();
        float l1, r1, l2, r2;
        if (info.device->isStereo()) {
                if (balance < 0) {
                        float b = (balance + 100.0f) / 100.0f;
                        l1 = volume;
                        r1 = 0.0f;
                        l2 = volume * sqrtf(std::max(0.0f, 1.0f - b));
                        r2 = volume * sqrtf(std::max(0.0f,        b));
                } else {
                        float b = balance / 100.0f;
                        l1 = volume * sqrtf(std::max(0.0f, 1.0f - b));
                        r1 = volume * sqrtf(std::max(0.0f,        b));
                        l2 = 0.0f;
                        r2 = volume;
                }
        } else {
                // make sure that in case of rounding errors
                // we don't take sqrt() of negative numbers
                float b = (balance + 100.0f) / 200.0f;
                l1 = volume * sqrtf(std::max(0.0f, 1.0f - b));
                r1 = volume * sqrtf(std::max(0.0f,        b));
                l2 = r2 = 0.0f; // dummy
        }
        float ampL, ampR;
        std::tie(ampL, ampR) = info.device->getAmplificationFactor();
        info.left1  = l1 * ampL;
        info.right1 = r1 * ampR;
        info.left2  = l2 * ampL;
        info.right2 = r2 * ampR;
}

void MSXMixer::updateMasterVolume()
{
        for (auto& p : infos) {
                updateVolumeParams(p);
        }
}

void MSXMixer::updateSoftwareVolume(SoundDevice& device)
{
        auto it = find_if_unguarded(infos,
                [&](auto& i) { return i.device == &device; });
        updateVolumeParams(*it);
}

void MSXMixer::executeUntil(EmuTime::param time)
{
        updateStream(time);
        reschedule2();

        // This method gets called very regularly, typically 44100/512 = 86x
        // per second (even if sound is muted and even with sound_driver=null).
        // This rate is constant in real-time (compared to e.g. the VDP sync
        // points that are constant in emutime). So we can use this to
        // regularly exit from the main CPU emulation loop. Without this there
        // were problems like described in 'bug#563 Console very slow when
        // setting speed to low values like 1'.
        motherBoard.exitCPULoopSync();
}


// Sound device info

SoundDevice* MSXMixer::findDevice(std::string_view name) const
{
        auto it = ranges::find_if(infos, [&](auto& i) {
                return i.device->getName() == name;
        });
        return (it != end(infos)) ? it->device : nullptr;
}

MSXMixer::SoundDeviceInfoTopic::SoundDeviceInfoTopic(
                InfoCommand& machineInfoCommand)
        : InfoTopic(machineInfoCommand, "sounddevice")
{
}

void MSXMixer::SoundDeviceInfoTopic::execute(
        span<const TclObject> tokens, TclObject& result) const
{
        auto& msxMixer = OUTER(MSXMixer, soundDeviceInfo);
        switch (tokens.size()) {
        case 2:
                result.addListElements(view::transform(
                        msxMixer.infos,
                        [](auto& info) { return info.device->getName(); }));
                break;
        case 3: {
                SoundDevice* device = msxMixer.findDevice(tokens[2].getString());
                if (!device) {
                        throw CommandException("Unknown sound device");
                }
                result = device->getDescription();
                break;
        }
        default:
                throw CommandException("Too many parameters");
        }
}

string MSXMixer::SoundDeviceInfoTopic::help(const vector<string>& /*tokens*/) const
{
        return "Shows a list of available sound devices.\n";
}

void MSXMixer::SoundDeviceInfoTopic::tabCompletion(vector<string>& tokens) const
{
        if (tokens.size() == 3) {
                auto devices = to_vector(view::transform(
                        OUTER(MSXMixer, soundDeviceInfo).infos,
                        [](auto& info) { return info.device->getName(); }));
                completeString(tokens, devices);
        }
}

} // namespace openmsx