AudioCore: Skeleton Implementation

This commit:
* Adds a new subproject, audio_core.
* Defines structures that exist in DSP shared memory.
* Hooks up various other parts of the emulator into audio core.

This sets the foundation for a later HLE DSP implementation.

src/audio_core/audio_core.cpp

@@ -0,0 +1,53 @@
+// Copyright 2016 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "audio_core/audio_core.h"
+#include "audio_core/hle/dsp.h"
+
+#include "core/core_timing.h"
+#include "core/hle/kernel/vm_manager.h"
+#include "core/hle/service/dsp_dsp.h"
+
+namespace AudioCore {
+
+// Audio Ticks occur about every 5 miliseconds.
+static int tick_event;                               ///< CoreTiming event
+static constexpr u64 audio_frame_ticks = 1310252ull; ///< Units: ARM11 cycles
+
+static void AudioTickCallback(u64 /*userdata*/, int cycles_late) {
+    if (DSP::HLE::Tick()) {
+        // HACK: We're not signaling the interrups when they should be, but just firing them all off together.
+        // It should be only (interrupt_id = 2, channel_id = 2) that's signalled here.
+        // TODO(merry): Understand when the other interrupts are fired.
+        DSP_DSP::SignalAllInterrupts();
+    }
+
+    // Reschedule recurrent event
+    CoreTiming::ScheduleEvent(audio_frame_ticks - cycles_late, tick_event);
+}
+
+/// Initialise Audio
+void Init() {
+    DSP::HLE::Init();
+
+    tick_event = CoreTiming::RegisterEvent("AudioCore::tick_event", AudioTickCallback);
+    CoreTiming::ScheduleEvent(audio_frame_ticks, tick_event);
+}
+
+/// Add DSP address spaces to Process's address space.
+void AddAddressSpace(Kernel::VMManager& address_space) {
+    auto r0_vma = address_space.MapBackingMemory(DSP::HLE::region0_base, reinterpret_cast<u8*>(&DSP::HLE::g_region0), sizeof(DSP::HLE::SharedMemory), Kernel::MemoryState::IO).MoveFrom();
+    address_space.Reprotect(r0_vma, Kernel::VMAPermission::ReadWrite);
+
+    auto r1_vma = address_space.MapBackingMemory(DSP::HLE::region1_base, reinterpret_cast<u8*>(&DSP::HLE::g_region1), sizeof(DSP::HLE::SharedMemory), Kernel::MemoryState::IO).MoveFrom();
+    address_space.Reprotect(r1_vma, Kernel::VMAPermission::ReadWrite);
+}
+
+/// Shutdown Audio
+void Shutdown() {
+    CoreTiming::UnscheduleEvent(tick_event, 0);
+    DSP::HLE::Shutdown();
+}
+
+} //namespace