Merge pull request #842 from bunnei/audio-core

Initial implementation of Audio Core

src/CMakeLists.txt

@@ -3,6 +3,7 @@ include_directories(.)
 
 add_subdirectory(common)
 add_subdirectory(core)
+add_subdirectory(audio_core)
 add_subdirectory(video_core)
 add_subdirectory(input_common)
 add_subdirectory(tests)

src/audio_core/CMakeLists.txt

@@ -0,0 +1,11 @@
+add_library(audio_core STATIC
+    audio_out.cpp
+    audio_out.h
+    buffer.h
+    stream.cpp
+    stream.h
+)
+
+create_target_directory_groups(audio_core)
+
+target_link_libraries(audio_core PUBLIC common core)

src/audio_core/audio_out.cpp

@@ -0,0 +1,50 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "audio_core/audio_out.h"
+#include "common/assert.h"
+#include "common/logging/log.h"
+
+namespace AudioCore {
+
+/// Returns the stream format from the specified number of channels
+static Stream::Format ChannelsToStreamFormat(int num_channels) {
+    switch (num_channels) {
+    case 1:
+        return Stream::Format::Mono16;
+    case 2:
+        return Stream::Format::Stereo16;
+    case 6:
+        return Stream::Format::Multi51Channel16;
+    }
+
+    LOG_CRITICAL(Audio, "Unimplemented num_channels={}", num_channels);
+    UNREACHABLE();
+    return {};
+}
+
+StreamPtr AudioOut::OpenStream(int sample_rate, int num_channels,
+                               Stream::ReleaseCallback&& release_callback) {
+    streams.push_back(std::make_shared<Stream>(sample_rate, ChannelsToStreamFormat(num_channels),
+                                               std::move(release_callback)));
+    return streams.back();
+}
+
+std::vector<u64> AudioOut::GetTagsAndReleaseBuffers(StreamPtr stream, size_t max_count) {
+    return stream->GetTagsAndReleaseBuffers(max_count);
+}
+
+void AudioOut::StartStream(StreamPtr stream) {
+    stream->Play();
+}
+
+void AudioOut::StopStream(StreamPtr stream) {
+    stream->Stop();
+}
+
+bool AudioOut::QueueBuffer(StreamPtr stream, Buffer::Tag tag, std::vector<u8>&& data) {
+    return stream->QueueBuffer(std::make_shared<Buffer>(tag, std::move(data)));
+}
+
+} // namespace AudioCore

src/audio_core/audio_out.h

@@ -0,0 +1,44 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include <vector>
+
+#include "audio_core/buffer.h"
+#include "audio_core/stream.h"
+#include "common/common_types.h"
+
+namespace AudioCore {
+
+using StreamPtr = std::shared_ptr<Stream>;
+
+/**
+ * Represents an audio playback interface, used to open and play audio streams
+ */
+class AudioOut {
+public:
+    /// Opens a new audio stream
+    StreamPtr OpenStream(int sample_rate, int num_channels,
+                         Stream::ReleaseCallback&& release_callback);
+
+    /// Returns a vector of recently released buffers specified by tag for the specified stream
+    std::vector<u64> GetTagsAndReleaseBuffers(StreamPtr stream, size_t max_count);
+
+    /// Starts an audio stream for playback
+    void StartStream(StreamPtr stream);
+
+    /// Stops an audio stream that is currently playing
+    void StopStream(StreamPtr stream);
+
+    /// Queues a buffer into the specified audio stream, returns true on success
+    bool QueueBuffer(StreamPtr stream, Buffer::Tag tag, std::vector<u8>&& data);
+
+private:
+    /// Active audio streams on the interface
+    std::vector<StreamPtr> streams;
+};
+
+} // namespace AudioCore

src/audio_core/buffer.h

@@ -0,0 +1,37 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <vector>
+
+#include "common/common_types.h"
+
+namespace AudioCore {
+
+/**
+ * Represents a buffer of audio samples to be played in an audio stream
+ */
+class Buffer {
+public:
+    using Tag = u64;
+
+    Buffer(Tag tag, std::vector<u8>&& data) : tag{tag}, data{std::move(data)} {}
+
+    /// Returns the raw audio data for the buffer
+    const std::vector<u8>& GetData() const {
+        return data;
+    }
+
+    /// Returns the buffer tag, this is provided by the game to the audout service
+    Tag GetTag() const {
+        return tag;
+    }
+
+private:
+    Tag tag;
+    std::vector<u8> data;
+};
+
+} // namespace AudioCore

src/audio_core/stream.cpp

@@ -0,0 +1,103 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "common/assert.h"
+#include "common/logging/log.h"
+#include "core/core_timing.h"
+#include "core/core_timing_util.h"
+
+#include "audio_core/stream.h"
+
+namespace AudioCore {
+
+constexpr size_t MaxAudioBufferCount{32};
+
+/// Returns the sample size for the specified audio stream format
+static size_t SampleSizeFromFormat(Stream::Format format) {
+    switch (format) {
+    case Stream::Format::Mono16:
+        return 2;
+    case Stream::Format::Stereo16:
+        return 4;
+    case Stream::Format::Multi51Channel16:
+        return 12;
+    };
+
+    LOG_CRITICAL(Audio, "Unimplemented format={}", static_cast<u32>(format));
+    UNREACHABLE();
+    return {};
+}
+
+Stream::Stream(int sample_rate, Format format, ReleaseCallback&& release_callback)
+    : sample_rate{sample_rate}, format{format}, release_callback{std::move(release_callback)} {
+    release_event = CoreTiming::RegisterEvent(
+        "Stream::Release", [this](u64 userdata, int cycles_late) { ReleaseActiveBuffer(); });
+}
+
+void Stream::Play() {
+    state = State::Playing;
+    PlayNextBuffer();
+}
+
+void Stream::Stop() {
+    ASSERT_MSG(false, "Unimplemented");
+}
+
+s64 Stream::GetBufferReleaseCycles(const Buffer& buffer) const {
+    const size_t num_samples{buffer.GetData().size() / SampleSizeFromFormat(format)};
+    return CoreTiming::usToCycles((static_cast<u64>(num_samples) * 1000000) / sample_rate);
+}
+
+void Stream::PlayNextBuffer() {
+    if (!IsPlaying()) {
+        // Ensure we are in playing state before playing the next buffer
+        return;
+    }
+
+    if (active_buffer) {
+        // Do not queue a new buffer if we are already playing a buffer
+        return;
+    }
+
+    if (queued_buffers.empty()) {
+        // No queued buffers - we are effectively paused
+        return;
+    }
+
+    active_buffer = queued_buffers.front();
+    queued_buffers.pop();
+
+    CoreTiming::ScheduleEventThreadsafe(GetBufferReleaseCycles(*active_buffer), release_event, {});
+}
+
+void Stream::ReleaseActiveBuffer() {
+    released_buffers.push(std::move(active_buffer));
+    release_callback();
+    PlayNextBuffer();
+}
+
+bool Stream::QueueBuffer(BufferPtr&& buffer) {
+    if (queued_buffers.size() < MaxAudioBufferCount) {
+        queued_buffers.push(std::move(buffer));
+        PlayNextBuffer();
+        return true;
+    }
+    return false;
+}
+
+bool Stream::ContainsBuffer(Buffer::Tag tag) const {
+    ASSERT_MSG(false, "Unimplemented");
+    return {};
+}
+
+std::vector<Buffer::Tag> Stream::GetTagsAndReleaseBuffers(size_t max_count) {
+    std::vector<Buffer::Tag> tags;
+    for (size_t count = 0; count < max_count && !released_buffers.empty(); ++count) {
+        tags.push_back(released_buffers.front()->GetTag());
+        released_buffers.pop();
+    }
+    return tags;
+}
+
+} // namespace AudioCore

src/audio_core/stream.h

@@ -0,0 +1,89 @@
+// Copyright 2018 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <functional>
+#include <memory>
+#include <vector>
+#include <queue>
+
+#include "audio_core/buffer.h"
+#include "common/assert.h"
+#include "common/common_types.h"
+#include "core/core_timing.h"
+
+namespace AudioCore {
+
+using BufferPtr = std::shared_ptr<Buffer>;
+
+/**
+ * Represents an audio stream, which is a sequence of queued buffers, to be outputed by AudioOut
+ */
+class Stream {
+public:
+    /// Audio format of the stream
+    enum class Format {
+        Mono16,
+        Stereo16,
+        Multi51Channel16,
+    };
+
+    /// Callback function type, used to change guest state on a buffer being released
+    using ReleaseCallback = std::function<void()>;
+
+    Stream(int sample_rate, Format format, ReleaseCallback&& release_callback);
+
+    /// Plays the audio stream
+    void Play();
+
+    /// Stops the audio stream
+    void Stop();
+
+    /// Queues a buffer into the audio stream, returns true on success
+    bool QueueBuffer(BufferPtr&& buffer);
+
+    /// Returns true if the audio stream contains a buffer with the specified tag
+    bool ContainsBuffer(Buffer::Tag tag) const;
+
+    /// Returns a vector of recently released buffers specified by tag
+    std::vector<Buffer::Tag> GetTagsAndReleaseBuffers(size_t max_count);
+
+    /// Returns true if the stream is currently playing
+    bool IsPlaying() const {
+        return state == State::Playing;
+    }
+
+    /// Returns the number of queued buffers
+    size_t GetQueueSize() const {
+        return queued_buffers.size();
+    }
+
+private:
+    /// Current state of the stream
+    enum class State {
+        Stopped,
+        Playing,
+    };
+
+    /// Plays the next queued buffer in the audio stream, starting playback if necessary
+    void PlayNextBuffer();
+
+    /// Releases the actively playing buffer, signalling that it has been completed
+    void ReleaseActiveBuffer();
+
+    /// Gets the number of core cycles when the specified buffer will be released
+    s64 GetBufferReleaseCycles(const Buffer& buffer) const;
+
+    int sample_rate;                        ///< Sample rate of the stream
+    Format format;                          ///< Format of the stream
+    ReleaseCallback release_callback;       ///< Buffer release callback for the stream
+    State state{State::Stopped};            ///< Playback state of the stream
+    CoreTiming::EventType* release_event{}; ///< Core timing release event for the stream
+    BufferPtr active_buffer;                ///< Actively playing buffer in the stream
+    std::queue<BufferPtr> queued_buffers;   ///< Buffers queued to be played in the stream
+    std::queue<BufferPtr> released_buffers; ///< Buffers recently released from the stream
+};
+
+} // namespace AudioCore

src/core/CMakeLists.txt

@@ -309,7 +309,7 @@ add_library(core STATIC
 
 create_target_directory_groups(core)
 
-target_link_libraries(core PUBLIC common PRIVATE video_core)
+target_link_libraries(core PUBLIC common PRIVATE audio_core video_core)
 target_link_libraries(core PUBLIC Boost::boost PRIVATE fmt lz4_static unicorn)
 
 if (ARCHITECTURE_x86_64)

src/core/core.cpp

@@ -177,6 +177,7 @@ System::ResultStatus System::Init(EmuWindow* emu_window, u32 system_mode) {
     }
 
     gpu_core = std::make_unique<Tegra::GPU>();
+    audio_core = std::make_unique<AudioCore::AudioOut>();
     telemetry_session = std::make_unique<Core::TelemetrySession>();
     service_manager = std::make_shared<Service::SM::ServiceManager>();
 
@@ -228,6 +229,7 @@ void System::Shutdown() {
     service_manager.reset();
     telemetry_session.reset();
     gpu_core.reset();
+    audio_core.reset();
 
     // Close all CPU/threading state
     cpu_barrier->NotifyEnd();

src/core/core.h

@@ -8,6 +8,7 @@
 #include <memory>
 #include <string>
 #include <thread>
+#include "audio_core/audio_out.h"
 #include "common/common_types.h"
 #include "core/arm/exclusive_monitor.h"
 #include "core/core_cpu.h"
@@ -131,6 +132,11 @@ public:
         return *gpu_core;
     }
 
+    /// Gets the AudioCore interface
+    AudioCore::AudioOut& AudioCore() {
+        return *audio_core;
+    }
+
     /// Gets the scheduler for the CPU core that is currently running
     Kernel::Scheduler& CurrentScheduler() {
         return *CurrentCpuCore().Scheduler();
@@ -195,6 +201,7 @@ private:
     /// AppLoader used to load the current executing application
     std::unique_ptr<Loader::AppLoader> app_loader;
     std::unique_ptr<Tegra::GPU> gpu_core;
+    std::unique_ptr<AudioCore::AudioOut> audio_core;
     std::shared_ptr<Tegra::DebugContext> debug_context;
     Kernel::SharedPtr<Kernel::Process> current_process;
     std::shared_ptr<ExclusiveMonitor> cpu_exclusive_monitor;

src/core/hle/service/audio/audout_u.cpp

@@ -5,8 +5,7 @@
 #include <array>
 #include <vector>
 #include "common/logging/log.h"
-#include "core/core_timing.h"
-#include "core/core_timing_util.h"
+#include "core/core.h"
 #include "core/hle/ipc_helpers.h"
 #include "core/hle/kernel/event.h"
 #include "core/hle/kernel/hle_ipc.h"
@@ -14,17 +13,22 @@
 
 namespace Service::Audio {
 
-/// Switch sample rate frequency
-constexpr u32 sample_rate{48000};
-/// TODO(st4rk): dynamic number of channels, as I think Switch has support
-/// to more audio channels (probably when Docked I guess)
-constexpr u32 audio_channels{2};
-/// TODO(st4rk): find a proper value for the audio_ticks
-constexpr u64 audio_ticks{static_cast<u64>(CoreTiming::BASE_CLOCK_RATE / 500)};
+namespace ErrCodes {
+enum {
+    ErrorUnknown = 2,
+    BufferCountExceeded = 8,
+};
+}
+
+constexpr std::array<char, 10> DefaultDevice{{"DeviceOut"}};
+constexpr int DefaultSampleRate{48000};
 
 class IAudioOut final : public ServiceFramework<IAudioOut> {
 public:
-    IAudioOut() : ServiceFramework("IAudioOut"), audio_out_state(AudioState::Stopped) {
+    IAudioOut(AudoutParams audio_params)
+        : ServiceFramework("IAudioOut"), audio_params(audio_params),
+          audio_core(Core::System::GetInstance().AudioCore()) {
+
         static const FunctionInfo functions[] = {
             {0, &IAudioOut::GetAudioOutState, "GetAudioOutState"},
             {1, &IAudioOut::StartAudioOut, "StartAudioOut"},
@@ -32,66 +36,65 @@ public:
             {3, &IAudioOut::AppendAudioOutBufferImpl, "AppendAudioOutBuffer"},
             {4, &IAudioOut::RegisterBufferEvent, "RegisterBufferEvent"},
             {5, &IAudioOut::GetReleasedAudioOutBufferImpl, "GetReleasedAudioOutBuffer"},
-            {6, nullptr, "ContainsAudioOutBuffer"},
+            {6, &IAudioOut::ContainsAudioOutBuffer, "ContainsAudioOutBuffer"},
             {7, &IAudioOut::AppendAudioOutBufferImpl, "AppendAudioOutBufferAuto"},
             {8, &IAudioOut::GetReleasedAudioOutBufferImpl, "GetReleasedAudioOutBufferAuto"},
-            {9, nullptr, "GetAudioOutBufferCount"},
+            {9, &IAudioOut::GetAudioOutBufferCount, "GetAudioOutBufferCount"},
             {10, nullptr, "GetAudioOutPlayedSampleCount"},
             {11, nullptr, "FlushAudioOutBuffers"},
         };
         RegisterHandlers(functions);
 
         // This is the event handle used to check if the audio buffer was released
-        buffer_event =
-            Kernel::Event::Create(Kernel::ResetType::OneShot, "IAudioOutBufferReleasedEvent");
+        buffer_event = Kernel::Event::Create(Kernel::ResetType::Sticky, "IAudioOutBufferReleased");
 
-        // Register event callback to update the Audio Buffer
-        audio_event = CoreTiming::RegisterEvent(
-            "IAudioOut::UpdateAudioBuffersCallback", [this](u64 userdata, int cycles_late) {
-                UpdateAudioBuffersCallback();
-                CoreTiming::ScheduleEvent(audio_ticks - cycles_late, audio_event);
-            });
-
-        // Start the audio event
-        CoreTiming::ScheduleEvent(audio_ticks, audio_event);
-    }
-
-    ~IAudioOut() {
-        CoreTiming::UnscheduleEvent(audio_event, 0);
+        stream = audio_core.OpenStream(audio_params.sample_rate, audio_params.channel_count,
+                                       [=]() { buffer_event->Signal(); });
     }
 
 private:
+    struct AudioBuffer {
+        u64_le next;
+        u64_le buffer;
+        u64_le buffer_capacity;
+        u64_le buffer_size;
+        u64_le offset;
+    };
+    static_assert(sizeof(AudioBuffer) == 0x28, "AudioBuffer is an invalid size");
+
     void GetAudioOutState(Kernel::HLERequestContext& ctx) {
         LOG_DEBUG(Service_Audio, "called");
         IPC::ResponseBuilder rb{ctx, 3};
         rb.Push(RESULT_SUCCESS);
-        rb.Push(static_cast<u32>(audio_out_state));
+        rb.Push(static_cast<u32>(stream->IsPlaying() ? AudioState::Started : AudioState::Stopped));
     }
 
     void StartAudioOut(Kernel::HLERequestContext& ctx) {
-        LOG_WARNING(Service_Audio, "(STUBBED) called");
+        LOG_DEBUG(Service_Audio, "called");
 
-        // Start audio
-        audio_out_state = AudioState::Started;
+        if (stream->IsPlaying()) {
+            IPC::ResponseBuilder rb{ctx, 2};
+            rb.Push(ResultCode(ErrorModule::Audio, ErrCodes::ErrorUnknown));
+            return;
+        }
+
+        audio_core.StartStream(stream);
 
         IPC::ResponseBuilder rb{ctx, 2};
         rb.Push(RESULT_SUCCESS);
     }
 
     void StopAudioOut(Kernel::HLERequestContext& ctx) {
-        LOG_WARNING(Service_Audio, "(STUBBED) called");
+        LOG_DEBUG(Service_Audio, "called");
 
-        // Stop audio
-        audio_out_state = AudioState::Stopped;
-
-        queue_keys.clear();
+        audio_core.StopStream(stream);
 
         IPC::ResponseBuilder rb{ctx, 2};
         rb.Push(RESULT_SUCCESS);
     }
 
     void RegisterBufferEvent(Kernel::HLERequestContext& ctx) {
-        LOG_WARNING(Service_Audio, "(STUBBED) called");
+        LOG_DEBUG(Service_Audio, "called");
 
         IPC::ResponseBuilder rb{ctx, 2, 1};
         rb.Push(RESULT_SUCCESS);
@@ -99,101 +102,107 @@ private:
     }
 
     void AppendAudioOutBufferImpl(Kernel::HLERequestContext& ctx) {
-        LOG_WARNING(Service_Audio, "(STUBBED) called");
+        LOG_DEBUG(Service_Audio, "(STUBBED) called {}", ctx.Description());
         IPC::RequestParser rp{ctx};
 
-        const u64 key{rp.Pop<u64>()};
-        queue_keys.insert(queue_keys.begin(), key);
+        const auto& input_buffer{ctx.ReadBuffer()};
+        ASSERT_MSG(input_buffer.size() == sizeof(AudioBuffer),
+                   "AudioBuffer input is an invalid size!");
+        AudioBuffer audio_buffer{};
+        std::memcpy(&audio_buffer, input_buffer.data(), sizeof(AudioBuffer));
+        const u64 tag{rp.Pop<u64>()};
+
+        std::vector<u8> data(audio_buffer.buffer_size);
+        Memory::ReadBlock(audio_buffer.buffer, data.data(), data.size());
+
+        if (!audio_core.QueueBuffer(stream, tag, std::move(data))) {
+            IPC::ResponseBuilder rb{ctx, 2};
+            rb.Push(ResultCode(ErrorModule::Audio, ErrCodes::BufferCountExceeded));
+        }
 
         IPC::ResponseBuilder rb{ctx, 2};
         rb.Push(RESULT_SUCCESS);
     }
 
     void GetReleasedAudioOutBufferImpl(Kernel::HLERequestContext& ctx) {
-        LOG_WARNING(Service_Audio, "(STUBBED) called");
+        LOG_DEBUG(Service_Audio, "called {}", ctx.Description());
+        IPC::RequestParser rp{ctx};
+        const u64 max_count{ctx.GetWriteBufferSize() / sizeof(u64)};
+        const auto released_buffers{audio_core.GetTagsAndReleaseBuffers(stream, max_count)};
 
-        // TODO(st4rk): This is how libtransistor currently implements the
-        // GetReleasedAudioOutBuffer, it should return the key (a VAddr) to the app and this address
-        // is used to know which buffer should be filled with data and send again to the service
-        // through AppendAudioOutBuffer. Check if this is the proper way to do it.
-        u64 key{0};
-
-        if (queue_keys.size()) {
-            key = queue_keys.back();
-            queue_keys.pop_back();
-        }
-
-        ctx.WriteBuffer(&key, sizeof(u64));
+        std::vector<u64> tags{released_buffers};
+        tags.resize(max_count);
+        ctx.WriteBuffer(tags);
 
         IPC::ResponseBuilder rb{ctx, 3};
         rb.Push(RESULT_SUCCESS);
-        // TODO(st4rk): This might be the total of released buffers, needs to be verified on
-        // hardware
-        rb.Push<u32>(static_cast<u32>(queue_keys.size()));
+        rb.Push<u32>(static_cast<u32>(released_buffers.size()));
     }
 
-    void UpdateAudioBuffersCallback() {
-        if (audio_out_state != AudioState::Started) {
-            return;
-        }
-
-        if (queue_keys.empty()) {
-            return;
-        }
-
-        buffer_event->Signal();
+    void ContainsAudioOutBuffer(Kernel::HLERequestContext& ctx) {
+        LOG_DEBUG(Service_Audio, "called");
+        IPC::RequestParser rp{ctx};
+        const u64 tag{rp.Pop<u64>()};
+        IPC::ResponseBuilder rb{ctx, 3};
+        rb.Push(RESULT_SUCCESS);
+        rb.Push(stream->ContainsBuffer(tag));
     }
 
-    enum class AudioState : u32 {
-        Started,
-        Stopped,
-    };
+    void GetAudioOutBufferCount(Kernel::HLERequestContext& ctx) {
+        LOG_DEBUG(Service_Audio, "called");
+        IPC::ResponseBuilder rb{ctx, 3};
+        rb.Push(RESULT_SUCCESS);
+        rb.Push(static_cast<u32>(stream->GetQueueSize()));
+    }
 
-    /// This is used to trigger the audio event callback that is going to read the samples from the
-    /// audio_buffer list and enqueue the samples using the sink (audio_core).
-    CoreTiming::EventType* audio_event;
+    AudioCore::AudioOut& audio_core;
+    AudioCore::StreamPtr stream;
+
+    AudoutParams audio_params{};
 
     /// This is the evend handle used to check if the audio buffer was released
     Kernel::SharedPtr<Kernel::Event> buffer_event;
-
-    /// (st4rk): This is just a temporary workaround for the future implementation. Libtransistor
-    /// uses the key as an address in the App, so we need to return when the
-    /// GetReleasedAudioOutBuffer_1 is called, otherwise we'll run in problems, because
-    /// libtransistor uses the key returned as an pointer.
-    std::vector<u64> queue_keys;
-
-    AudioState audio_out_state;
 };
 
 void AudOutU::ListAudioOutsImpl(Kernel::HLERequestContext& ctx) {
-    LOG_WARNING(Service_Audio, "(STUBBED) called");
+    LOG_DEBUG(Service_Audio, "called");
     IPC::RequestParser rp{ctx};
 
-    constexpr std::array<char, 15> audio_interface{{"AudioInterface"}};
-    ctx.WriteBuffer(audio_interface);
+    ctx.WriteBuffer(DefaultDevice);
 
     IPC::ResponseBuilder rb = rp.MakeBuilder(3, 0, 0);
 
     rb.Push(RESULT_SUCCESS);
-    // TODO(st4rk): We're currently returning only one audio interface (stringlist size). However,
-    // it's highly possible to have more than one interface (despite that libtransistor requires
-    // only one).
-    rb.Push<u32>(1);
+    rb.Push<u32>(1); // Amount of audio devices
 }
 
 void AudOutU::OpenAudioOutImpl(Kernel::HLERequestContext& ctx) {
-    LOG_WARNING(Service_Audio, "(STUBBED) called");
+    LOG_DEBUG(Service_Audio, "called");
 
-    if (!audio_out_interface) {
-        audio_out_interface = std::make_shared<IAudioOut>();
+    ctx.WriteBuffer(DefaultDevice);
+    IPC::RequestParser rp{ctx};
+    auto params{rp.PopRaw<AudoutParams>()};
+    if (params.channel_count <= 2) {
+        // Mono does not exist for audout
+        params.channel_count = 2;
+    } else {
+        params.channel_count = 6;
     }
+    if (!params.sample_rate) {
+        params.sample_rate = DefaultSampleRate;
+    }
+
+    // TODO(bunnei): Support more than one IAudioOut interface. When we add this, ListAudioOutsImpl
+    // will likely need to be updated as well.
+    ASSERT_MSG(!audio_out_interface, "Unimplemented");
+    audio_out_interface = std::make_shared<IAudioOut>(std::move(params));
 
     IPC::ResponseBuilder rb{ctx, 6, 0, 1};
     rb.Push(RESULT_SUCCESS);
-    rb.Push<u32>(sample_rate);
-    rb.Push<u32>(audio_channels);
+    rb.Push<u32>(DefaultSampleRate);
+    rb.Push<u32>(params.channel_count);
     rb.Push<u32>(static_cast<u32>(PcmFormat::Int16));
-    rb.Push<u32>(0); // This field is unknown
+    rb.Push<u32>(static_cast<u32>(AudioState::Stopped));
     rb.PushIpcInterface<Audio::IAudioOut>(audio_out_interface);
 }
 

src/core/hle/service/audio/audout_u.h

@@ -12,6 +12,18 @@ class HLERequestContext;
 
 namespace Service::Audio {
 
+struct AudoutParams {
+    s32_le sample_rate;
+    u16_le channel_count;
+    INSERT_PADDING_BYTES(2);
+};
+static_assert(sizeof(AudoutParams) == 0x8, "AudoutParams is an invalid size");
+
+enum class AudioState : u32 {
+    Started,
+    Stopped,
+};
+
 class IAudioOut;
 
 class AudOutU final : public ServiceFramework<AudOutU> {