service/am: Add basic implementation of ChangeMainAppletMasterVolume

All this does is supply a new volume level and a fade time in
nanoseconds for the volume transition to occur within.

src/core/hle/service/am/am.cpp

@@ -98,7 +98,7 @@ IAudioController::IAudioController() : ServiceFramework("IAudioController") {
         {0, &IAudioController::SetExpectedMasterVolume, "SetExpectedMasterVolume"},
         {1, &IAudioController::GetMainAppletExpectedMasterVolume, "GetMainAppletExpectedMasterVolume"},
         {2, &IAudioController::GetLibraryAppletExpectedMasterVolume, "GetLibraryAppletExpectedMasterVolume"},
-        {3, nullptr, "ChangeMainAppletMasterVolume"},
+        {3, &IAudioController::ChangeMainAppletMasterVolume, "ChangeMainAppletMasterVolume"},
         {4, &IAudioController::SetTransparentAudioRate, "SetTransparentVolumeRate"},
     };
     // clang-format on
@@ -139,6 +139,26 @@ void IAudioController::GetLibraryAppletExpectedMasterVolume(Kernel::HLERequestCo
     rb.Push(library_applet_volume);
 }
 
+void IAudioController::ChangeMainAppletMasterVolume(Kernel::HLERequestContext& ctx) {
+    struct Parameters {
+        float volume;
+        s64 fade_time_ns;
+    };
+    static_assert(sizeof(Parameters) == 16);
+
+    IPC::RequestParser rp{ctx};
+    const auto parameters = rp.PopRaw<Parameters>();
+
+    LOG_DEBUG(Service_AM, "called. volume={}, fade_time_ns={}", parameters.volume,
+              parameters.fade_time_ns);
+
+    main_applet_volume = std::clamp(parameters.volume, min_allowed_volume, max_allowed_volume);
+    fade_time_ns = std::chrono::nanoseconds{parameters.fade_time_ns};
+
+    IPC::ResponseBuilder rb{ctx, 2};
+    rb.Push(RESULT_SUCCESS);
+}
+
 void IAudioController::SetTransparentAudioRate(Kernel::HLERequestContext& ctx) {
     IPC::RequestParser rp{ctx};
     const float transparent_volume_rate_tmp = rp.Pop<float>();

src/core/hle/service/am/am.h

@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <chrono>
 #include <memory>
 #include <queue>
 #include "core/hle/kernel/writable_event.h"
@@ -81,6 +82,7 @@ private:
     void SetExpectedMasterVolume(Kernel::HLERequestContext& ctx);
     void GetMainAppletExpectedMasterVolume(Kernel::HLERequestContext& ctx);
     void GetLibraryAppletExpectedMasterVolume(Kernel::HLERequestContext& ctx);
+    void ChangeMainAppletMasterVolume(Kernel::HLERequestContext& ctx);
     void SetTransparentAudioRate(Kernel::HLERequestContext& ctx);
 
     static constexpr float min_allowed_volume = 0.0f;
@@ -89,6 +91,12 @@ private:
     float main_applet_volume{0.25f};
     float library_applet_volume{max_allowed_volume};
     float transparent_volume_rate{min_allowed_volume};
+
+    // Volume transition fade time in nanoseconds.
+    // e.g. If the main applet volume was 0% and was changed to 50%
+    //      with a fade of 50ns, then over the course of 50ns,
+    //      the volume will gradually fade up to 50%
+    std::chrono::nanoseconds fade_time_ns{0};
 };
 
 class IDisplayController final : public ServiceFramework<IDisplayController> {