Implement event-based scheduler instead of lock-step components

src/common/audio_stream.cpp

@@ -59,34 +59,34 @@ void AudioStream::Shutdown()
   m_output_paused = true;
 }
 
-void AudioStream::BeginWrite(SampleType** buffer_ptr, u32* num_samples)
+void AudioStream::BeginWrite(SampleType** buffer_ptr, u32* num_frames)
 {
   m_buffer_mutex.lock();
 
   EnsureBuffer();
 
   Buffer& buffer = m_buffers[m_first_free_buffer];
-  *buffer_ptr = buffer.data.data() + buffer.write_position;
+  *buffer_ptr = buffer.data.data() + (buffer.write_position * m_channels);
-  *num_samples = m_buffer_size - buffer.write_position;
+  *num_frames = m_buffer_size - buffer.write_position;
 }
 
-void AudioStream::WriteSamples(const SampleType* samples, u32 num_samples)
+void AudioStream::WriteFrames(const SampleType* frames, u32 num_frames)
 {
-  u32 remaining_samples = num_samples;
+  u32 remaining_frames = num_frames;
   std::unique_lock<std::mutex> lock(m_buffer_mutex);
 
-  while (remaining_samples > 0)
+  while (remaining_frames > 0)
   {
     EnsureBuffer();
 
     Buffer& buffer = m_buffers[m_first_free_buffer];
-    const u32 to_this_buffer = std::min(m_buffer_size - buffer.write_position, remaining_samples);
+    const u32 to_this_buffer = std::min(m_buffer_size - buffer.write_position, remaining_frames);
 
     const u32 copy_count = to_this_buffer * m_channels;
-    std::memcpy(&buffer.data[buffer.write_position * m_channels], samples, copy_count * sizeof(SampleType));
+    std::memcpy(&buffer.data[buffer.write_position * m_channels], frames, copy_count * sizeof(SampleType));
-    samples += copy_count;
+    frames += copy_count;
 
-    remaining_samples -= to_this_buffer;
+    remaining_frames -= to_this_buffer;
     buffer.write_position += to_this_buffer;
 
     // End of the buffer?
@@ -102,11 +102,11 @@ void AudioStream::WriteSamples(const SampleType* samples, u32 num_samples)
   }
 }
 
-void AudioStream::EndWrite(u32 num_samples)
+void AudioStream::EndWrite(u32 num_frames)
 {
   Buffer& buffer = m_buffers[m_first_free_buffer];
-  DebugAssert((buffer.write_position + num_samples) <= m_buffer_size);
+  DebugAssert((buffer.write_position + num_frames) <= m_buffer_size);
-  buffer.write_position += num_samples;
+  buffer.write_position += num_frames;
 
   // End of the buffer?
   if (buffer.write_position == m_buffer_size)

src/common/audio_stream.h

@@ -37,9 +37,9 @@ public:
 
   void Shutdown();
 
-  void BeginWrite(SampleType** buffer_ptr, u32* num_samples);
+  void BeginWrite(SampleType** buffer_ptr, u32* num_frames);
-  void WriteSamples(const SampleType* samples, u32 num_samples);
+  void WriteFrames(const SampleType* frames, u32 num_frames);
-  void EndWrite(u32 num_samples);
+  void EndWrite(u32 num_frames);
 
   static std::unique_ptr<AudioStream> CreateNullAudioStream();
 

src/core/CMakeLists.txt

@@ -65,6 +65,8 @@ add_library(core
     system.h
     timers.cpp
     timers.h
+    timing_event.cpp
+    timing_event.h
     types.h
 )
 

src/core/cdrom.cpp

@@ -1,6 +1,6 @@
 #include "cdrom.h"
-#include "common/log.h"
 #include "common/cd_image.h"
+#include "common/log.h"
 #include "common/state_wrapper.h"
 #include "dma.h"
 #include "imgui.h"
@@ -22,6 +22,10 @@ void CDROM::Initialize(System* system, DMA* dma, InterruptController* interrupt_
   m_dma = dma;
   m_interrupt_controller = interrupt_controller;
   m_spu = spu;
+  m_command_event =
+    m_system->CreateTimingEvent("CDROM Command Event", 1, 1, std::bind(&CDROM::ExecuteCommand, this), false);
+  m_drive_event = m_system->CreateTimingEvent("CDROM Drive Event", 1, 1,
+                                              std::bind(&CDROM::ExecuteDrive, this, std::placeholders::_2), false);
 }
 
 void CDROM::Reset()
@@ -35,9 +39,9 @@ void CDROM::Reset()
 void CDROM::SoftReset()
 {
   m_command = Command::None;
+  m_command_event->Deactivate();
   m_drive_state = DriveState::Idle;
-  m_command_remaining_ticks = 0;
+  m_drive_event->Deactivate();
-  m_drive_remaining_ticks = 0;
   m_status.bits = 0;
   m_secondary_status.bits = 0;
   m_mode.bits = 0;
@@ -85,8 +89,6 @@ bool CDROM::DoState(StateWrapper& sw)
 {
   sw.Do(&m_command);
   sw.Do(&m_drive_state);
-  sw.Do(&m_command_remaining_ticks);
-  sw.Do(&m_drive_remaining_ticks);
   sw.Do(&m_status.bits);
   sw.Do(&m_secondary_status.bits);
   sw.Do(&m_mode.bits);
@@ -124,10 +126,8 @@ bool CDROM::DoState(StateWrapper& sw)
 
   if (sw.IsReading())
   {
-    if (HasPendingCommand())
+    UpdateCommandEvent();
-      m_system->SetDowncount(m_command_remaining_ticks);
+    m_drive_event->SetState(!IsDriveIdle());
-    if (!IsDriveIdle())
-      m_system->SetDowncount(m_drive_remaining_ticks);
 
     // load up media if we had something in there before
     if (m_media && !m_media->Seek(media_lba))
@@ -361,8 +361,8 @@ void CDROM::WriteRegister(u32 offset, u8 value)
           {
             if (HasPendingAsyncInterrupt())
               DeliverAsyncInterrupt();
-            else if (HasPendingCommand())
+            else
-              m_system->SetDowncount(m_command_remaining_ticks);
+              UpdateCommandEvent();
           }
 
           // Bit 6 clears the parameter FIFO.
@@ -443,6 +443,7 @@ void CDROM::DeliverAsyncInterrupt()
   m_pending_async_interrupt = 0;
   UpdateInterruptRequest();
   UpdateStatusRegister();
+  UpdateCommandEvent();
 }
 
 void CDROM::SendACKAndStat()
@@ -520,73 +521,11 @@ TickCount CDROM::GetTicksForSeek() const
   return ticks;
 }
 
-void CDROM::Execute(TickCount ticks)
-{
-  if (HasPendingCommand() && !HasPendingInterrupt())
-  {
-    m_command_remaining_ticks -= ticks;
-    if (m_command_remaining_ticks <= 0)
-      ExecuteCommand();
-    else
-      m_system->SetDowncount(m_command_remaining_ticks);
-  }
-
-  if (m_drive_state != DriveState::Idle)
-  {
-    m_drive_remaining_ticks -= ticks;
-    if (m_drive_remaining_ticks <= 0)
-    {
-      switch (m_drive_state)
-      {
-        case DriveState::SpinningUp:
-          DoSpinUpComplete();
-          break;
-
-        case DriveState::SeekingPhysical:
-        case DriveState::SeekingLogical:
-          DoSeekComplete();
-          break;
-
-        case DriveState::Pausing:
-          DoPauseComplete();
-          break;
-
-        case DriveState::Stopping:
-          DoStopComplete();
-          break;
-
-        case DriveState::ReadingID:
-          DoIDRead();
-          break;
-
-        case DriveState::ReadingTOC:
-          DoTOCRead();
-          break;
-
-        case DriveState::Reading:
-        case DriveState::Playing:
-          DoSectorRead();
-          break;
-
-        case DriveState::Idle:
-        default:
-          break;
-      }
-    }
-    else
-    {
-      m_system->SetDowncount(m_drive_remaining_ticks);
-    }
-  }
-}
-
 void CDROM::BeginCommand(Command command)
 {
-  m_system->Synchronize();
-
   m_command = command;
-  m_command_remaining_ticks = GetAckDelayForCommand();
+  m_command_event->SetDowncount(GetAckDelayForCommand());
-  m_system->SetDowncount(m_command_remaining_ticks);
+  UpdateCommandEvent();
   UpdateStatusRegister();
 }
 
@@ -595,7 +534,7 @@ void CDROM::EndCommand()
   m_param_fifo.Clear();
 
   m_command = Command::None;
-  m_command_remaining_ticks = 0;
+  m_command_event->Deactivate();
   UpdateStatusRegister();
 }
 
@@ -645,7 +584,7 @@ void CDROM::ExecuteCommand()
         SendACKAndStat();
 
         m_drive_state = DriveState::ReadingID;
-        m_drive_remaining_ticks = 18000;
+        m_drive_event->Schedule(18000);
       }
 
       EndCommand();
@@ -664,7 +603,7 @@ void CDROM::ExecuteCommand()
         SendACKAndStat();
 
         m_drive_state = DriveState::ReadingTOC;
-        m_drive_remaining_ticks = MASTER_CLOCK / 2; // half a second
+        m_drive_event->Schedule(MASTER_CLOCK / 2); // half a second
       }
 
       EndCommand();
@@ -767,12 +706,12 @@ void CDROM::ExecuteCommand()
     case Command::Pause:
     {
       const bool was_reading = (m_drive_state == DriveState::Reading || m_drive_state == DriveState::Playing);
+      const TickCount pause_time = was_reading ? (m_mode.double_speed ? 2000000 : 1000000) : 7000;
       Log_DebugPrintf("CDROM pause command");
       SendACKAndStat();
 
       m_drive_state = DriveState::Pausing;
-      m_drive_remaining_ticks = was_reading ? (m_mode.double_speed ? 2000000 : 1000000) : 7000;
+      m_drive_event->Schedule(pause_time);
-      m_system->SetDowncount(m_drive_remaining_ticks);
 
       EndCommand();
       return;
@@ -781,12 +720,12 @@ void CDROM::ExecuteCommand()
     case Command::Stop:
     {
       const bool was_motor_on = m_secondary_status.motor_on;
+      const TickCount stop_time = was_motor_on ? (m_mode.double_speed ? 25000000 : 13000000) : 7000;
       Log_DebugPrintf("CDROM stop command");
       SendACKAndStat();
 
       m_drive_state = DriveState::Stopping;
-      m_drive_remaining_ticks = was_motor_on ? (m_mode.double_speed ? 25000000 : 13000000) : 7000;
+      m_drive_event->Schedule(stop_time);
-      m_system->SetDowncount(m_drive_remaining_ticks);
 
       EndCommand();
       return;
@@ -801,8 +740,7 @@ void CDROM::ExecuteCommand()
       m_mode.bits = 0;
 
       m_drive_state = DriveState::SpinningUp;
-      m_drive_remaining_ticks = 80000;
+      m_drive_event->Schedule(80000);
-      m_system->SetDowncount(m_drive_remaining_ticks);
 
       EndCommand();
       return;
@@ -821,8 +759,7 @@ void CDROM::ExecuteCommand()
         SendACKAndStat();
 
         m_drive_state = DriveState::SpinningUp;
-        m_drive_remaining_ticks = 80000;
+        m_drive_event->Schedule(80000);
-        m_system->SetDowncount(m_drive_remaining_ticks);
       }
 
       EndCommand();
@@ -1011,7 +948,62 @@ void CDROM::ExecuteTestCommand(u8 subcommand)
   }
 }
 
-void CDROM::BeginReading()
+void CDROM::UpdateCommandEvent()
+{
+  // if there's a pending interrupt, we can't execute the command yet
+  // so deactivate it until the interrupt is acknowledged
+  if (!HasPendingCommand() || HasPendingInterrupt())
+  {
+    m_command_event->Deactivate();
+    return;
+  }
+  else if (HasPendingCommand())
+  {
+    m_command_event->Activate();
+  }
+}
+
+void CDROM::ExecuteDrive(TickCount ticks_late)
+{
+  switch (m_drive_state)
+  {
+    case DriveState::SpinningUp:
+      DoSpinUpComplete();
+      break;
+
+    case DriveState::SeekingPhysical:
+    case DriveState::SeekingLogical:
+      DoSeekComplete(ticks_late);
+      break;
+
+    case DriveState::Pausing:
+      DoPauseComplete();
+      break;
+
+    case DriveState::Stopping:
+      DoStopComplete();
+      break;
+
+    case DriveState::ReadingID:
+      DoIDRead();
+      break;
+
+    case DriveState::ReadingTOC:
+      DoTOCRead();
+      break;
+
+    case DriveState::Reading:
+    case DriveState::Playing:
+      DoSectorRead();
+      break;
+
+    case DriveState::Idle:
+    default:
+      break;
+  }
+}
+
+void CDROM::BeginReading(TickCount ticks_late)
 {
   Log_DebugPrintf("Starting reading");
   if (m_setloc_pending)
@@ -1026,12 +1018,13 @@ void CDROM::BeginReading()
   // TODO: Should the sector buffer be cleared here?
   m_sector_buffer.clear();
 
+  const TickCount ticks = GetTicksForRead();
   m_drive_state = DriveState::Reading;
-  m_drive_remaining_ticks = GetTicksForRead();
+  m_drive_event->SetInterval(ticks);
-  m_system->SetDowncount(m_drive_remaining_ticks);
+  m_drive_event->Schedule(ticks - ticks_late);
 }
 
-void CDROM::BeginPlaying(u8 track_bcd)
+void CDROM::BeginPlaying(u8 track_bcd, TickCount ticks_late)
 {
   Log_DebugPrintf("Starting playing CDDA track %x", track_bcd);
   m_last_cdda_report_frame_nibble = 0xFF;
@@ -1063,9 +1056,10 @@ void CDROM::BeginPlaying(u8 track_bcd)
   // TODO: Should the sector buffer be cleared here?
   m_sector_buffer.clear();
 
+  const TickCount ticks = GetTicksForRead();
   m_drive_state = DriveState::Playing;
-  m_drive_remaining_ticks = GetTicksForRead();
+  m_drive_event->SetInterval(ticks);
-  m_system->SetDowncount(m_drive_remaining_ticks);
+  m_drive_event->Schedule(ticks - ticks_late);
 }
 
 void CDROM::BeginSeeking(bool logical, bool read_after_seek, bool play_after_seek)
@@ -1088,8 +1082,7 @@ void CDROM::BeginSeeking(bool logical, bool read_after_seek, bool play_after_see
   m_sector_buffer.clear();
 
   m_drive_state = logical ? DriveState::SeekingLogical : DriveState::SeekingPhysical;
-  m_drive_remaining_ticks = seek_time;
+  m_drive_event->SetIntervalAndSchedule(seek_time);
-  m_system->SetDowncount(m_drive_remaining_ticks);
 
   // Read sub-q early.. this is because we're not reading sectors while seeking.
   // Fixes music looping in Spyro.
@@ -1101,6 +1094,7 @@ void CDROM::BeginSeeking(bool logical, bool read_after_seek, bool play_after_see
 void CDROM::DoSpinUpComplete()
 {
   m_drive_state = DriveState::Idle;
+  m_drive_event->Deactivate();
 
   m_secondary_status.motor_on = true;
 
@@ -1109,10 +1103,11 @@ void CDROM::DoSpinUpComplete()
   SetAsyncInterrupt(Interrupt::INT2);
 }
 
-void CDROM::DoSeekComplete()
+void CDROM::DoSeekComplete(TickCount ticks_late)
 {
   const bool logical = (m_drive_state == DriveState::SeekingLogical);
   m_drive_state = DriveState::Idle;
+  m_drive_event->Deactivate();
   m_secondary_status.ClearActiveBits();
   m_sector_buffer.clear();
 
@@ -1145,11 +1140,11 @@ void CDROM::DoSeekComplete()
     // INT2 is not sent on play/read
     if (m_read_after_seek)
     {
-      BeginReading();
+      BeginReading(ticks_late);
     }
     else if (m_play_after_seek)
     {
-      BeginPlaying(m_play_track_number_bcd);
+      BeginPlaying(m_play_track_number_bcd, ticks_late);
     }
     else
     {
@@ -1175,6 +1170,7 @@ void CDROM::DoPauseComplete()
 {
   Log_DebugPrintf("Pause complete");
   m_drive_state = DriveState::Idle;
+  m_drive_event->Deactivate();
   m_secondary_status.ClearActiveBits();
   m_sector_buffer.clear();
 
@@ -1187,6 +1183,7 @@ void CDROM::DoStopComplete()
 {
   Log_DebugPrintf("Stop complete");
   m_drive_state = DriveState::Idle;
+  m_drive_event->Deactivate();
   m_secondary_status.ClearActiveBits();
   m_secondary_status.motor_on = false;
   m_sector_buffer.clear();
@@ -1204,6 +1201,7 @@ void CDROM::DoIDRead()
 
   Log_DebugPrintf("ID read complete");
   m_drive_state = DriveState::Idle;
+  m_drive_event->Deactivate();
   m_secondary_status.ClearActiveBits();
   m_secondary_status.motor_on = true;
   m_sector_buffer.clear();
@@ -1219,6 +1217,7 @@ void CDROM::DoTOCRead()
 {
   Log_DebugPrintf("TOC read complete");
   m_drive_state = DriveState::Idle;
+  m_drive_event->Deactivate();
   m_async_response_fifo.Clear();
   m_async_response_fifo.Push(m_secondary_status.bits);
   SetAsyncInterrupt(Interrupt::INT2);
@@ -1254,6 +1253,7 @@ void CDROM::DoSectorRead()
 
       m_secondary_status.ClearActiveBits();
       m_drive_state = DriveState::Idle;
+      m_drive_event->Deactivate();
       return;
     }
   }
@@ -1290,9 +1290,6 @@ void CDROM::DoSectorRead()
     Log_DevPrintf("Skipping sector %u [%02u:%02u:%02u] due to invalid subchannel Q", m_media->GetPositionOnDisc() - 1,
                   pos.minute, pos.second, pos.frame);
   }
-
-  m_drive_remaining_ticks += GetTicksForRead();
-  m_system->SetDowncount(m_drive_remaining_ticks);
 }
 
 void CDROM::ProcessDataSectorHeader(const u8* raw_sector, bool set_valid)
@@ -1711,7 +1708,7 @@ void CDROM::DrawDebugWindow()
     if (HasPendingCommand())
     {
       ImGui::TextColored(active_color, "Command: 0x%02X (%d ticks remaining)", static_cast<u8>(m_command),
-                         m_command_remaining_ticks);
+                         m_command_event->IsActive() ? m_command_event->GetTicksUntilNextExecution() : 0);
     }
     else
     {
@@ -1725,7 +1722,8 @@ void CDROM::DrawDebugWindow()
     else
     {
       ImGui::TextColored(active_color, "Drive: %s (%d ticks remaining)",
-                         drive_state_names[static_cast<u8>(m_drive_state)], m_drive_remaining_ticks);
+                         drive_state_names[static_cast<u8>(m_drive_state)],
+                         m_drive_event->IsActive() ? m_drive_event->GetTicksUntilNextExecution() : 0);
     }
 
     ImGui::Text("Interrupt Enable Register: 0x%02X", m_interrupt_enable_register);

src/core/cdrom.h

@@ -12,6 +12,7 @@
 class StateWrapper;
 
 class System;
+class TimingEvent;
 class DMA;
 class InterruptController;
 class SPU;
@@ -36,8 +37,6 @@ public:
   void WriteRegister(u32 offset, u8 value);
   void DMARead(u32* words, u32 word_count);
 
-  void Execute(TickCount ticks);
-
   // Render statistics debug window.
   void DrawDebugWindow();
 
@@ -198,10 +197,12 @@ private:
   void EndCommand();                  // also updates status register
   void ExecuteCommand();
   void ExecuteTestCommand(u8 subcommand);
-  void BeginReading();
+  void UpdateCommandEvent();
-  void BeginPlaying(u8 track_bcd);
+  void ExecuteDrive(TickCount ticks_late);
+  void BeginReading(TickCount ticks_late = 0);
+  void BeginPlaying(u8 track_bcd, TickCount ticks_late = 0);
   void DoSpinUpComplete();
-  void DoSeekComplete();
+  void DoSeekComplete(TickCount ticks_late);
   void DoPauseComplete();
   void DoStopComplete();
   void DoIDRead();
@@ -219,11 +220,11 @@ private:
   InterruptController* m_interrupt_controller = nullptr;
   SPU* m_spu = nullptr;
   std::unique_ptr<CDImage> m_media;
+  std::unique_ptr<TimingEvent> m_command_event;
+  std::unique_ptr<TimingEvent> m_drive_event;
 
   Command m_command = Command::None;
   DriveState m_drive_state = DriveState::Idle;
-  TickCount m_command_remaining_ticks = 0;
-  TickCount m_drive_remaining_ticks = 0;
 
   StatusRegister m_status = {};
   SecondaryStatusRegister m_secondary_status = {};

src/core/core.vcxproj

@@ -82,6 +82,7 @@
     <ClCompile Include="spu.cpp" />
     <ClCompile Include="system.cpp" />
     <ClCompile Include="timers.cpp" />
+    <ClCompile Include="timing_event.cpp" />
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="analog_controller.h" />
@@ -121,6 +122,7 @@
     <ClInclude Include="spu.h" />
     <ClInclude Include="system.h" />
     <ClInclude Include="timers.h" />
+    <ClInclude Include="timing_event.h" />
     <ClInclude Include="types.h" />
   </ItemGroup>
   <ItemGroup>

src/core/core.vcxproj.filters

@@ -39,6 +39,7 @@
     <ClCompile Include="controller.cpp" />
     <ClCompile Include="analog_controller.cpp" />
     <ClCompile Include="host_display.cpp" />
+    <ClCompile Include="timing_event.cpp" />
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="types.h" />
@@ -79,6 +80,7 @@
     <ClInclude Include="sio.h" />
     <ClInclude Include="controller.h" />
     <ClInclude Include="analog_controller.h" />
+    <ClInclude Include="timing_event.h" />
   </ItemGroup>
   <ItemGroup>
     <None Include="cpu_core.inl" />

src/core/cpu_core.h

@@ -51,11 +51,8 @@ public:
   ALWAYS_INLINE void ResetPendingTicks() { m_pending_ticks = 0; }
   ALWAYS_INLINE void AddPendingTicks(TickCount ticks) { m_pending_ticks += ticks; }
 
-  ALWAYS_INLINE void SetDowncount(TickCount downcount)
+  ALWAYS_INLINE TickCount GetDowncount() const { return m_downcount; }
-  {
+  ALWAYS_INLINE void SetDowncount(TickCount downcount) { m_downcount = downcount; }
-    m_downcount = (downcount < m_downcount) ? downcount : m_downcount;
-  }
-  ALWAYS_INLINE void ResetDowncount() { m_downcount = MAX_SLICE_SIZE; }
 
   // Sets the PC and flushes the pipeline.
   void SetPC(u32 new_pc);

src/core/dma.cpp

@@ -1,8 +1,9 @@
 #include "dma.h"
-#include "common/log.h"
 #include "bus.h"
 #include "cdrom.h"
+#include "common/log.h"
 #include "common/state_wrapper.h"
+#include "common/string_util.h"
 #include "gpu.h"
 #include "interrupt_controller.h"
 #include "mdec.h"
@@ -25,14 +26,28 @@ void DMA::Initialize(System* system, Bus* bus, InterruptController* interrupt_co
   m_spu = spu;
   m_mdec = mdec;
   m_transfer_buffer.resize(32);
+
+  for (u32 i = 0; i < NUM_CHANNELS; i++)
+  {
+    m_state[i].transfer_event = system->CreateTimingEvent(
+      StringUtil::StdStringFromFormat("DMA%u Transfer", i), 1, 1,
+      std::bind(&DMA::TransferChannel, this, static_cast<Channel>(i), std::placeholders::_2), false);
+  }
 }
 
 void DMA::Reset()
 {
-  m_transfer_in_progress = false;
-  std::memset(&m_state, 0, sizeof(m_state));
   m_DPCR.bits = 0x07654321;
   m_DICR.bits = 0;
+  for (u32 i = 0; i < NUM_CHANNELS; i++)
+  {
+    ChannelState& cs = m_state[i];
+    cs.base_address = 0;
+    cs.block_control.bits = 0;
+    cs.channel_control.bits = 0;
+    cs.request = false;
+    cs.transfer_event->Deactivate();
+  }
 }
 
 bool DMA::DoState(StateWrapper& sw)
@@ -43,7 +58,6 @@ bool DMA::DoState(StateWrapper& sw)
     sw.Do(&cs.base_address);
     sw.Do(&cs.block_control.bits);
     sw.Do(&cs.channel_control.bits);
-    sw.Do(&cs.transfer_ticks);
     sw.Do(&cs.request);
   }
 
@@ -52,13 +66,11 @@ bool DMA::DoState(StateWrapper& sw)
 
   if (sw.IsReading())
   {
-    m_transfer_min_ticks = std::numeric_limits<TickCount>::max();
+    for (u32 i = 0; i < NUM_CHANNELS; i++)
-    for (const ChannelState& cs : m_state)
     {
-      if (cs.transfer_ticks > 0)
+      m_state[i].transfer_event->Deactivate();
-        m_transfer_min_ticks = std::min(m_transfer_min_ticks, cs.transfer_ticks);
+      UpdateChannelTransferEvent(static_cast<Channel>(i));
     }
-    m_system->SetDowncount(m_transfer_min_ticks);
   }
 
   return !sw.HasError();
@@ -126,7 +138,7 @@ void DMA::WriteRegister(u32 offset, u32 value)
       {
         Log_TracePrintf("DMA channel %u block control <- 0x%08X", channel_index, value);
         state.block_control.bits = value;
-        QueueTransferChannel(static_cast<Channel>(channel_index));
+        UpdateChannelTransferEvent(static_cast<Channel>(channel_index));
         return;
       }
 
@@ -135,7 +147,7 @@ void DMA::WriteRegister(u32 offset, u32 value)
         state.channel_control.bits = (state.channel_control.bits & ~ChannelState::ChannelControl::WRITE_MASK) |
                                      (value & ChannelState::ChannelControl::WRITE_MASK);
         Log_TracePrintf("DMA channel %u channel control <- 0x%08X", channel_index, state.channel_control.bits);
-        QueueTransferChannel(static_cast<Channel>(channel_index));
+        UpdateChannelTransferEvent(static_cast<Channel>(channel_index));
         return;
       }
 
@@ -151,7 +163,8 @@ void DMA::WriteRegister(u32 offset, u32 value)
       {
         Log_TracePrintf("DPCR <- 0x%08X", value);
         m_DPCR.bits = value;
-        QueueTransfer();
+        for (u32 i = 0; i < NUM_CHANNELS; i++)
+          UpdateChannelTransferEvent(static_cast<Channel>(i));
         return;
       }
 
@@ -180,7 +193,7 @@ void DMA::SetRequest(Channel channel, bool request)
 
   cs.request = request;
   if (request)
-    QueueTransfer();
+    UpdateChannelTransferEvent(channel);
 }
 
 TickCount DMA::GetTransferDelay(Channel channel) const
@@ -188,6 +201,10 @@ TickCount DMA::GetTransferDelay(Channel channel) const
   const ChannelState& cs = m_state[static_cast<u32>(channel)];
   switch (channel)
   {
+    case Channel::MDECin:
+    case Channel::MDECout:
+      return 1;
+
     case Channel::SPU:
     {
       if (cs.channel_control.sync_mode == SyncMode::Request)
@@ -198,7 +215,7 @@ TickCount DMA::GetTransferDelay(Channel channel) const
     break;
 
     default:
-      return 1;
+      return 0;
   }
 }
 
@@ -217,9 +234,6 @@ bool DMA::CanTransferChannel(Channel channel) const
   if (cs.channel_control.sync_mode == SyncMode::Manual && !cs.channel_control.start_trigger)
     return false;
 
-  if (cs.transfer_ticks > 0)
-    return false;
-
   return true;
 }
 
@@ -244,72 +258,34 @@ void DMA::UpdateIRQ()
   }
 }
 
-void DMA::QueueTransferChannel(Channel channel)
+void DMA::UpdateChannelTransferEvent(Channel channel)
 {
   ChannelState& cs = m_state[static_cast<u32>(channel)];
-  if (cs.transfer_ticks > 0 || !CanTransferChannel(channel))
+  if (!CanTransferChannel(channel))
+  {
+    cs.transfer_event->Deactivate();
+    return;
+  }
+
+  if (cs.transfer_event->IsActive())
     return;
 
   const TickCount ticks = GetTransferDelay(channel);
   if (ticks == 0)
   {
     // immediate transfer
-    TransferChannel(channel);
+    TransferChannel(channel, 0);
     return;
   }
 
-  if (!m_transfer_in_progress)
+  cs.transfer_event->SetPeriodAndSchedule(ticks);
-    m_system->Synchronize();
-
-  cs.transfer_ticks = ticks;
-  m_transfer_min_ticks = std::min(m_transfer_min_ticks, ticks);
-  m_system->SetDowncount(ticks);
 }
 
-void DMA::QueueTransfer()
+void DMA::TransferChannel(Channel channel, TickCount ticks_late)
-{
-  for (u32 i = 0; i < NUM_CHANNELS; i++)
-    QueueTransferChannel(static_cast<Channel>(i));
-}
-
-void DMA::Execute(TickCount ticks)
-{
-  m_transfer_min_ticks -= ticks;
-  if (m_transfer_min_ticks > 0)
-  {
-    m_system->SetDowncount(m_transfer_min_ticks);
-    return;
-  }
-
-  DebugAssert(!m_transfer_in_progress);
-  m_transfer_in_progress = true;
-
-  // keep going until all transfers are done. one channel can start others (e.g. MDEC)
-  m_transfer_min_ticks = std::numeric_limits<TickCount>::max();
-  for (u32 i = 0; i < NUM_CHANNELS; i++)
-  {
-    const Channel channel = static_cast<Channel>(i);
-    if (m_state[i].transfer_ticks <= 0)
-      continue;
-
-    m_state[i].transfer_ticks -= ticks;
-    if (CanTransferChannel(channel))
-    {
-      TransferChannel(channel);
-    }
-    else
-    {
-      m_transfer_min_ticks = std::min(m_transfer_min_ticks, ticks);
-    }
-  }
-
-  m_system->SetDowncount(m_transfer_min_ticks);
-  m_transfer_in_progress = false;
-}
-
-void DMA::TransferChannel(Channel channel)
 {
   ChannelState& cs = m_state[static_cast<u32>(channel)];
+  cs.transfer_event->Deactivate();
+
   const bool copy_to_device = cs.channel_control.copy_to_device;
 
   // start/trigger bit is cleared on beginning of transfer
@@ -416,7 +392,6 @@ void DMA::TransferChannel(Channel channel)
   }
 
   // start/busy bit is cleared on end of transfer
-  cs.transfer_ticks = 0;
   cs.channel_control.enable_busy = false;
   if (m_DICR.IsIRQEnabled(channel))
   {

src/core/dma.h

@@ -2,11 +2,13 @@
 #include "common/bitfield.h"
 #include "types.h"
 #include <array>
+#include <memory>
 #include <vector>
 
 class StateWrapper;
 
 class System;
+class TimingEvent;
 class Bus;
 class InterruptController;
 class GPU;
@@ -49,8 +51,6 @@ public:
   // changing interfaces
   void SetGPU(GPU* gpu) { m_gpu = gpu; }
 
-  void Execute(TickCount ticks);
-
 private:
   static constexpr PhysicalMemoryAddress BASE_ADDRESS_MASK = UINT32_C(0x00FFFFFF);
   static constexpr PhysicalMemoryAddress ADDRESS_MASK = UINT32_C(0x001FFFFC);
@@ -72,10 +72,8 @@ private:
   bool CanRunAnyChannels() const;
   void UpdateIRQ();
 
-  void QueueTransferChannel(Channel channel);
+  void UpdateChannelTransferEvent(Channel channel);
-  void QueueTransfer();
+  void TransferChannel(Channel channel, TickCount ticks_late);
-
-  void TransferChannel(Channel channel);
 
   // from device -> memory
   void TransferDeviceToMemory(Channel channel, u32 address, u32 increment, u32 word_count);
@@ -95,6 +93,7 @@ private:
 
   struct ChannelState
   {
+    std::unique_ptr<TimingEvent> transfer_event;
     u32 base_address;
 
     union BlockControl
@@ -131,7 +130,6 @@ private:
       static constexpr u32 WRITE_MASK = 0b01110001'01110111'00000111'00000011;
     } channel_control;
 
-    TickCount transfer_ticks = 0;
     bool request = false;
   };
 
@@ -207,7 +205,4 @@ private:
       master_flag = master_enable && ((((bits >> 16) & u32(0b1111111)) & ((bits >> 24) & u32(0b1111111))) != 0);
     }
   } m_DICR = {};
-
-  TickCount m_transfer_min_ticks = 0;
-  bool m_transfer_in_progress = false;
 };

src/core/gpu.cpp

@@ -1,6 +1,6 @@
 #include "gpu.h"
-#include "common/log.h"
 #include "common/heap_array.h"
+#include "common/log.h"
 #include "common/state_wrapper.h"
 #include "dma.h"
 #include "host_interface.h"
@@ -27,6 +27,8 @@ bool GPU::Initialize(HostDisplay* host_display, System* system, DMA* dma, Interr
   m_interrupt_controller = interrupt_controller;
   m_timers = timers;
   m_force_progressive_scan = m_system->GetSettings().gpu_force_progressive_scan;
+  m_tick_event =
+    m_system->CreateTimingEvent("GPU Tick", 1, 1, std::bind(&GPU::Execute, this, std::placeholders::_1), true);
   return true;
 }
 
@@ -63,6 +65,9 @@ void GPU::SoftReset()
   m_draw_mode.SetTextureWindow(0);
   UpdateGPUSTAT();
   UpdateCRTCConfig();
+
+  m_tick_event->Deactivate();
+  UpdateSliceTicks();
 }
 
 bool GPU::DoState(StateWrapper& sw)
@@ -273,6 +278,11 @@ void GPU::DMAWrite(const u32* words, u32 word_count)
   }
 }
 
+void GPU::Synchronize()
+{
+  m_tick_event->InvokeEarly();
+}
+
 void GPU::UpdateCRTCConfig()
 {
   static constexpr std::array<TickCount, 8> dot_clock_dividers = {{10, 8, 5, 4, 7, 7, 7, 7}};
@@ -357,31 +367,31 @@ void GPU::UpdateCRTCConfig()
 
   // Ensure the numbers are sane, and not due to a misconfigured active display range.
   cs.display_aspect_ratio = (std::isnormal(display_ratio) && display_ratio != 0.0f) ? display_ratio : (4.0f / 3.0f);
+  m_tick_event->SetInterval(cs.horizontal_total);
+}
 
-  UpdateSliceTicks();
+static TickCount GPUTicksToSystemTicks(u32 gpu_ticks)
+{
+  // convert to master clock, rounding up as we want to overshoot not undershoot
+  return (gpu_ticks * 7 + 10) / 11;
 }
 
 void GPU::UpdateSliceTicks()
 {
-  // the next event is at the end of the next scanline
+  // figure out how many GPU ticks until the next vblank
-#if 1
+  const u32 lines_until_vblank =
-  TickCount ticks_until_next_event;
+    (m_crtc_state.current_scanline >= m_crtc_state.vertical_display_end ?
-  if (m_crtc_state.current_tick_in_scanline < m_crtc_state.horizontal_display_start)
+       (m_crtc_state.vertical_total - m_crtc_state.current_scanline + m_crtc_state.vertical_display_end) :
-    ticks_until_next_event = m_crtc_state.horizontal_display_start - m_crtc_state.current_tick_in_scanline;
+       (m_crtc_state.vertical_display_end - m_crtc_state.current_scanline));
-  else if (m_crtc_state.current_tick_in_scanline < m_crtc_state.horizontal_display_end)
+  const u32 ticks_until_vblank =
-    ticks_until_next_event = m_crtc_state.horizontal_display_end - m_crtc_state.current_tick_in_scanline;
+    lines_until_vblank * m_crtc_state.horizontal_total - m_crtc_state.current_tick_in_scanline;
-  else
+  const u32 ticks_until_hblank =
-    ticks_until_next_event = m_crtc_state.horizontal_total - m_crtc_state.current_tick_in_scanline;
+    (m_crtc_state.current_tick_in_scanline >= m_crtc_state.horizontal_display_end) ?
-#else
+      (m_crtc_state.horizontal_total - m_crtc_state.current_tick_in_scanline + m_crtc_state.horizontal_display_end) :
-  // or at vblank. this will depend on the timer config..
+      (m_crtc_state.horizontal_display_end - m_crtc_state.current_tick_in_scanline);
-  const TickCount ticks_until_next_event =
-    ((m_crtc_state.vertical_total - m_crtc_state.current_scanline) * m_crtc_state.horizontal_total) -
-    m_crtc_state.current_tick_in_scanline;
-#endif
 
-  // convert to master clock, rounding up as we want to overshoot not undershoot
+  m_tick_event->Schedule(GPUTicksToSystemTicks(ticks_until_vblank));
-  const TickCount system_ticks = (ticks_until_next_event * 7 + 10) / 11;
+  m_tick_event->SetPeriod(GPUTicksToSystemTicks(ticks_until_hblank));
-  m_system->SetDowncount(system_ticks);
 }
 
 void GPU::Execute(TickCount ticks)
@@ -393,13 +403,76 @@ void GPU::Execute(TickCount ticks)
     m_crtc_state.fractional_ticks = temp % 7;
   }
 
-  while (m_crtc_state.current_tick_in_scanline >= m_crtc_state.horizontal_total)
+  if (m_crtc_state.current_tick_in_scanline < m_crtc_state.horizontal_total)
   {
-    m_crtc_state.current_tick_in_scanline -= m_crtc_state.horizontal_total;
+    // short path when we execute <1 line.. this shouldn't occur often.
-    m_crtc_state.current_scanline++;
+    const bool old_hblank = m_crtc_state.in_hblank;
+    const bool new_hblank = m_crtc_state.current_tick_in_scanline < m_crtc_state.horizontal_display_start ||
+                            m_crtc_state.current_tick_in_scanline >= m_crtc_state.horizontal_display_end;
+    if (!old_hblank && new_hblank && m_timers->IsUsingExternalClock(HBLANK_TIMER_INDEX))
+      m_timers->AddTicks(HBLANK_TIMER_INDEX, 1);
+
+    UpdateSliceTicks();
+    return;
+  }
+
+  u32 lines_to_draw = m_crtc_state.current_tick_in_scanline / m_crtc_state.horizontal_total;
+  m_crtc_state.current_tick_in_scanline %= m_crtc_state.horizontal_total;
+#if 0
+  Log_WarningPrintf("Old line: %u, new line: %u, drawing %u", m_crtc_state.current_scanline,
+                    m_crtc_state.current_scanline + lines_to_draw, lines_to_draw);
+#endif
+
+  const bool old_hblank = m_crtc_state.in_hblank;
+  const bool new_hblank = m_crtc_state.current_tick_in_scanline < m_crtc_state.horizontal_display_start ||
+                          m_crtc_state.current_tick_in_scanline >= m_crtc_state.horizontal_display_end;
+  m_crtc_state.in_hblank = new_hblank;
+  if (m_timers->IsUsingExternalClock(HBLANK_TIMER_INDEX))
+  {
+    const u32 hblank_timer_ticks = BoolToUInt32(!old_hblank) + BoolToUInt32(new_hblank) + (lines_to_draw - 1);
+    m_timers->AddTicks(HBLANK_TIMER_INDEX, static_cast<TickCount>(hblank_timer_ticks));
+  }
+
+  while (lines_to_draw > 0)
+  {
+    const u32 lines_to_draw_this_loop =
+      std::min(lines_to_draw, m_crtc_state.vertical_total - m_crtc_state.current_scanline);
+    const u32 prev_scanline = m_crtc_state.current_scanline;
+    m_crtc_state.current_scanline += lines_to_draw_this_loop;
+    DebugAssert(m_crtc_state.current_scanline <= m_crtc_state.vertical_total);
+    lines_to_draw -= lines_to_draw_this_loop;
+
+    // clear the vblank flag if the beam would pass through the display area
+    if (prev_scanline < m_crtc_state.vertical_display_start &&
+        m_crtc_state.current_scanline >= m_crtc_state.vertical_display_end)
+    {
+      m_crtc_state.in_vblank = false;
+    }
+
+    const bool new_vblank = m_crtc_state.current_scanline < m_crtc_state.vertical_display_start ||
+                            m_crtc_state.current_scanline >= m_crtc_state.vertical_display_end;
+    if (m_crtc_state.in_vblank != new_vblank)
+    {
+      m_crtc_state.in_vblank = new_vblank;
+
+      if (new_vblank)
+      {
+        static u32 x = 0;
+        Log_DebugPrintf("Now in v-blank %u ticks %u hblanks", m_system->GetGlobalTickCounter() - x);
+        x = m_system->GetGlobalTickCounter();
+        m_interrupt_controller->InterruptRequest(InterruptController::IRQ::VBLANK);
+
+        // flush any pending draws and "scan out" the image
+        FlushRender();
+        UpdateDisplay();
+        m_system->IncrementFrameNumber();
+      }
+
+      m_timers->SetGate(HBLANK_TIMER_INDEX, new_vblank);
+    }
 
     // past the end of vblank?
-    if (m_crtc_state.current_scanline >= m_crtc_state.vertical_total)
+    if (m_crtc_state.current_scanline == m_crtc_state.vertical_total)
     {
       // start the new frame
       m_crtc_state.current_scanline = 0;
@@ -415,25 +488,6 @@ void GPU::Execute(TickCount ticks)
         m_GPUSTAT.interlaced_field = false;
       }
     }
-
-    const bool new_vblank = m_crtc_state.current_scanline < m_crtc_state.vertical_display_start ||
-                            m_crtc_state.current_scanline >= m_crtc_state.vertical_display_end;
-    if (m_crtc_state.in_vblank != new_vblank)
-    {
-      m_crtc_state.in_vblank = new_vblank;
-
-      if (new_vblank)
-      {
-        Log_DebugPrintf("Now in v-blank");
-        m_interrupt_controller->InterruptRequest(InterruptController::IRQ::VBLANK);
-
-        // flush any pending draws and "scan out" the image
-        FlushRender();
-        UpdateDisplay();
-        m_system->IncrementFrameNumber();
-      }
-
-      m_timers->SetGate(HBLANK_TIMER_INDEX, new_vblank);
   }
 
   // alternating even line bit in 240-line mode
@@ -447,16 +501,6 @@ void GPU::Execute(TickCount ticks)
     m_GPUSTAT.drawing_even_line =
       ConvertToBoolUnchecked((m_crtc_state.regs.Y + m_crtc_state.current_scanline) & u32(1));
   }
-  }
-
-  const bool new_hblank = m_crtc_state.current_tick_in_scanline < m_crtc_state.horizontal_display_start ||
-                          m_crtc_state.current_tick_in_scanline >= m_crtc_state.horizontal_display_end;
-  if (m_crtc_state.in_hblank != new_hblank)
-  {
-    m_crtc_state.in_hblank = new_hblank;
-    if (new_hblank && m_timers->IsUsingExternalClock(HBLANK_TIMER_INDEX))
-      m_timers->AddTicks(HBLANK_TIMER_INDEX, 1);
-  }
 
   UpdateSliceTicks();
 }
@@ -560,18 +604,30 @@ void GPU::WriteGP1(u32 value)
 
     case 0x06: // Set horizontal display range
     {
-      m_crtc_state.regs.horizontal_display_range = param & CRTCState::Regs::HORIZONTAL_DISPLAY_RANGE_MASK;
+      const u32 new_value = param & CRTCState::Regs::HORIZONTAL_DISPLAY_RANGE_MASK;
-      Log_DebugPrintf("Horizontal display range <- 0x%08X", m_crtc_state.regs.horizontal_display_range);
+      Log_DebugPrintf("Horizontal display range <- 0x%08X", new_value);
+
+      if (m_crtc_state.regs.horizontal_display_range != new_value)
+      {
+        m_tick_event->InvokeEarly(true);
+        m_crtc_state.regs.horizontal_display_range = new_value;
         UpdateCRTCConfig();
       }
+    }
     break;
 
     case 0x07: // Set display start address
     {
-      m_crtc_state.regs.vertical_display_range = param & CRTCState::Regs::VERTICAL_DISPLAY_RANGE_MASK;
+      const u32 new_value = param & CRTCState::Regs::VERTICAL_DISPLAY_RANGE_MASK;
-      Log_DebugPrintf("Vertical display range <- 0x%08X", m_crtc_state.regs.vertical_display_range);
+      Log_DebugPrintf("Vertical display range <- 0x%08X", new_value);
+
+      if (m_crtc_state.regs.vertical_display_range != new_value)
+      {
+        m_tick_event->InvokeEarly(true);
+        m_crtc_state.regs.vertical_display_range = new_value;
         UpdateCRTCConfig();
       }
+    }
     break;
 
     case 0x08: // Set display mode
@@ -590,17 +646,23 @@ void GPU::WriteGP1(u32 value)
       };
 
       const GP1_08h dm{param};
-      m_GPUSTAT.horizontal_resolution_1 = dm.horizontal_resolution_1;
+      GPUSTAT new_GPUSTAT{m_GPUSTAT.bits};
-      m_GPUSTAT.vertical_resolution = dm.vertical_resolution;
+      new_GPUSTAT.horizontal_resolution_1 = dm.horizontal_resolution_1;
-      m_GPUSTAT.pal_mode = dm.pal_mode;
+      new_GPUSTAT.vertical_resolution = dm.vertical_resolution;
-      m_GPUSTAT.display_area_color_depth_24 = dm.display_area_color_depth;
+      new_GPUSTAT.pal_mode = dm.pal_mode;
-      m_GPUSTAT.vertical_interlace = dm.vertical_interlace;
+      new_GPUSTAT.display_area_color_depth_24 = dm.display_area_color_depth;
-      m_GPUSTAT.horizontal_resolution_2 = dm.horizontal_resolution_2;
+      new_GPUSTAT.vertical_interlace = dm.vertical_interlace;
-      m_GPUSTAT.reverse_flag = dm.reverse_flag;
+      new_GPUSTAT.horizontal_resolution_2 = dm.horizontal_resolution_2;
-
+      new_GPUSTAT.reverse_flag = dm.reverse_flag;
       Log_DebugPrintf("Set display mode <- 0x%08X", dm.bits);
+
+      if (m_GPUSTAT.bits != new_GPUSTAT.bits)
+      {
+        m_tick_event->InvokeEarly(true);
+        m_GPUSTAT.bits = new_GPUSTAT.bits;
         UpdateCRTCConfig();
       }
+    }
     break;
 
     case 0x09: // Allow texture disable

src/core/gpu.h

@@ -15,6 +15,7 @@ class StateWrapper;
 class HostDisplay;
 
 class System;
+class TimingEvent;
 class DMA;
 class InterruptController;
 class Timers;
@@ -127,12 +128,12 @@ public:
   void DMARead(u32* words, u32 word_count);
   void DMAWrite(const u32* words, u32 word_count);
 
+  // Synchronizes the CRTC, updating the hblank timer.
+  void Synchronize();
+
   // Recompile shaders/recreate framebuffers when needed.
   virtual void UpdateSettings();
 
-  // Ticks for hblank/vblank.
-  void Execute(TickCount ticks);
-
   // gpu_hw_d3d11.cpp
   static std::unique_ptr<GPU> CreateHardwareD3D11Renderer();
 
@@ -299,6 +300,9 @@ protected:
   // Updates dynamic bits in GPUSTAT (ready to send VRAM/ready to receive DMA)
   void UpdateGPUSTAT();
 
+  // Ticks for hblank/vblank.
+  void Execute(TickCount ticks);
+
   /// Returns true if scanout should be interlaced.
   bool IsDisplayInterlaced() const { return !m_force_progressive_scan && m_GPUSTAT.In480iMode(); }
 
@@ -331,6 +335,8 @@ protected:
   InterruptController* m_interrupt_controller = nullptr;
   Timers* m_timers = nullptr;
 
+  std::unique_ptr<TimingEvent> m_tick_event;
+
   // Pointer to VRAM, used for reads/writes. In the hardware backends, this is the shadow buffer.
   u16* m_vram_ptr = nullptr;
 

src/core/host_interface.cpp

@@ -360,7 +360,7 @@ void HostInterface::Throttle()
   const s64 sleep_time = static_cast<s64>(m_last_throttle_time - time);
   if (std::abs(sleep_time) >= MAX_VARIANCE_TIME)
   {
-#ifdef Y_BUILD_CONFIG_RELEASE
+#ifndef _DEBUG
     // Don't display the slow messages in debug, it'll always be slow...
     // Limit how often the messages are displayed.
     if (m_speed_lost_time_timestamp.GetTimeSeconds() >= 1.0f)
@@ -437,6 +437,9 @@ void HostInterface::UpdateSpeedLimiterState()
                  (audio_sync_enabled && video_sync_enabled) ? " and video" : (video_sync_enabled ? "video" : ""));
 
   m_audio_stream->SetSync(audio_sync_enabled);
+  if (audio_sync_enabled)
+    m_audio_stream->EmptyBuffers();
+
   m_display->SetVSync(video_sync_enabled);
   m_throttle_timer.Reset();
   m_last_throttle_time = 0;

src/core/host_interface.h

@@ -68,6 +68,9 @@ public:
   /// Returns a path relative to the user directory.
   std::string GetUserDirectoryRelativePath(const char* format, ...) const;
 
+  /// Throttles the system, i.e. sleeps until it's time to execute the next frame.
+  void Throttle();
+
 protected:
   using ThrottleClock = std::chrono::steady_clock;
 
@@ -131,9 +134,6 @@ protected:
 
   void RunFrame();
 
-  /// Throttles the system, i.e. sleeps until it's time to execute the next frame.
-  void Throttle();
-
   void UpdateSpeedLimiterState();
 
   void DrawFPSWindow();

src/core/mdec.cpp

@@ -15,6 +15,8 @@ void MDEC::Initialize(System* system, DMA* dma)
 {
   m_system = system;
   m_dma = dma;
+  m_block_copy_out_event = system->CreateTimingEvent("MDEC Block Copy Out", TICKS_PER_BLOCK, TICKS_PER_BLOCK,
+                                                     std::bind(&MDEC::CopyOutBlock, this), false);
 }
 
 void MDEC::Reset()
@@ -39,8 +41,11 @@ bool MDEC::DoState(StateWrapper& sw)
   sw.Do(&m_current_coefficient);
   sw.Do(&m_current_q_scale);
   sw.Do(&m_block_rgb);
-  sw.Do(&m_block_copy_out_ticks);
+
-  sw.Do(&m_block_copy_out_pending);
+  bool block_copy_out_pending = HasPendingBlockCopyOut();
+  sw.Do(&block_copy_out_pending);
+  if (sw.IsReading())
+    m_block_copy_out_event->SetState(block_copy_out_pending);
 
   return !sw.HasError();
 }
@@ -131,6 +136,11 @@ void MDEC::DMAWrite(const u32* words, u32 word_count)
   } while (word_count > 0);
 }
 
+bool MDEC::HasPendingBlockCopyOut() const
+{
+  return m_block_copy_out_event->IsActive();
+}
+
 void MDEC::SoftReset()
 {
   m_status.bits = 0;
@@ -143,8 +153,7 @@ void MDEC::SoftReset()
   m_current_block = 0;
   m_current_coefficient = 64;
   m_current_q_scale = 0;
-  m_block_copy_out_ticks = TICKS_PER_BLOCK;
+  m_block_copy_out_event->Deactivate();
-  m_block_copy_out_pending = false;
   UpdateStatus();
 }
 
@@ -173,11 +182,10 @@ u32 MDEC::ReadDataRegister()
   if (m_data_out_fifo.IsEmpty())
   {
     // Stall the CPU until we're done processing.
-    if (m_block_copy_out_pending)
+    if (HasPendingBlockCopyOut())
     {
       Log_DevPrint("MDEC data out FIFO empty on read - stalling CPU");
-      m_system->StallCPU(m_block_copy_out_ticks);
+      m_system->StallCPU(m_block_copy_out_event->GetTicksUntilNextExecution());
-      Execute(m_block_copy_out_ticks);
     }
     else
     {
@@ -205,27 +213,9 @@ void MDEC::WriteCommandRegister(u32 value)
   ExecutePendingCommand();
 }
 
-void MDEC::Execute(TickCount ticks)
-{
-  if (!m_block_copy_out_pending)
-    return;
-
-  m_block_copy_out_ticks -= ticks;
-  if (m_block_copy_out_ticks <= 0)
-  {
-    DebugAssert(m_command == Command::DecodeMacroblock);
-    CopyOutBlock();
-
-    if (m_remaining_halfwords == 0)
-      EndCommand();
-    else
-      ExecutePendingCommand();
-  }
-}
-
 void MDEC::ExecutePendingCommand()
 {
-  if (m_block_copy_out_pending)
+  if (HasPendingBlockCopyOut())
   {
     // can't do anything while waiting
     UpdateStatus();
@@ -234,7 +224,7 @@ void MDEC::ExecutePendingCommand()
 
   while (!m_data_in_fifo.IsEmpty())
   {
-    DebugAssert(!m_block_copy_out_pending);
+    DebugAssert(!HasPendingBlockCopyOut());
 
     if (m_command == Command::None)
     {
@@ -417,20 +407,16 @@ bool MDEC::DecodeColoredMacroblock()
 
 void MDEC::ScheduleBlockCopyOut(TickCount ticks)
 {
-  DebugAssert(!m_block_copy_out_pending);
+  DebugAssert(!HasPendingBlockCopyOut());
   Log_DebugPrintf("Scheduling block copy out in %d ticks", ticks);
 
-  m_system->Synchronize();
+  m_block_copy_out_event->Schedule(TICKS_PER_BLOCK);
-  m_block_copy_out_pending = true;
-  m_block_copy_out_ticks = ticks;
-  m_system->SetDowncount(ticks);
 }
 
 void MDEC::CopyOutBlock()
 {
-  DebugAssert(m_block_copy_out_pending);
+  DebugAssert(m_command == Command::DecodeMacroblock);
-  m_block_copy_out_pending = false;
+  m_block_copy_out_event->Deactivate();
-  m_block_copy_out_ticks = 0;
 
   Log_DebugPrintf("Copying out block");
 
@@ -535,13 +521,9 @@ void MDEC::CopyOutBlock()
 
   // if we've copied out all blocks, command is complete
   if (m_remaining_halfwords == 0)
-  {
+    EndCommand();
-    DebugAssert(m_command == Command::DecodeMacroblock);
+  else
-    m_command = Command::None;
+    ExecutePendingCommand();
-    m_current_block = 0;
-    m_current_coefficient = 64;
-    m_current_q_scale = 0;
-  }
 }
 
 static constexpr std::array<u8, 64> zigzag = {{0,  1,  5,  6,  14, 15, 27, 28, 2,  4,  7,  13, 16, 26, 29, 42,

src/core/mdec.h

@@ -3,10 +3,12 @@
 #include "common/fifo_queue.h"
 #include "types.h"
 #include <array>
+#include <memory>
 
 class StateWrapper;
 
 class System;
+class TimingEvent;
 class DMA;
 
 class MDEC
@@ -26,8 +28,6 @@ public:
   void DMARead(u32* words, u32 word_count);
   void DMAWrite(const u32* words, u32 word_count);
 
-  void Execute(TickCount ticks);
-
   void DrawDebugStateWindow();
 
 private:
@@ -88,6 +88,7 @@ private:
   };
 
   bool HasPendingCommand() const { return m_command != Command::None; }
+  bool HasPendingBlockCopyOut() const;
 
   void SoftReset();
   void UpdateStatus();
@@ -138,8 +139,7 @@ private:
   u16 m_current_q_scale = 0;
 
   std::array<u32, 256> m_block_rgb{};
-  TickCount m_block_copy_out_ticks = TICKS_PER_BLOCK;
+  std::unique_ptr<TimingEvent> m_block_copy_out_event;
-  bool m_block_copy_out_pending = false;
 
   u32 m_total_blocks_decoded = 0;
 };

src/core/pad.cpp

@@ -16,6 +16,8 @@ void Pad::Initialize(System* system, InterruptController* interrupt_controller)
 {
   m_system = system;
   m_interrupt_controller = interrupt_controller;
+  m_transfer_event = system->CreateTimingEvent("Pad Serial Transfer", 1, 1,
+                                               std::bind(&Pad::TransferEvent, this, std::placeholders::_2), false);
 }
 
 void Pad::Reset()
@@ -81,7 +83,6 @@ bool Pad::DoState(StateWrapper& sw)
   }
 
   sw.Do(&m_state);
-  sw.Do(&m_ticks_remaining);
   sw.Do(&m_JOY_CTRL.bits);
   sw.Do(&m_JOY_STAT.bits);
   sw.Do(&m_JOY_MODE.bits);
@@ -91,6 +92,9 @@ bool Pad::DoState(StateWrapper& sw)
   sw.Do(&m_receive_buffer_full);
   sw.Do(&m_transmit_buffer_full);
 
+  if (sw.IsReading() && IsTransmitting())
+    m_transfer_event->Activate();
+
   return !sw.HasError();
 }
 
@@ -213,24 +217,6 @@ void Pad::WriteRegister(u32 offset, u32 value)
   }
 }
 
-void Pad::Execute(TickCount ticks)
-{
-  if (m_state == State::Idle)
-    return;
-
-  m_ticks_remaining -= ticks;
-  if (m_ticks_remaining > 0)
-  {
-    m_system->SetDowncount(m_ticks_remaining);
-    return;
-  }
-
-  if (m_state == State::Transmitting)
-    DoTransfer();
-  else
-    DoACK();
-}
-
 void Pad::SoftReset()
 {
   if (IsTransmitting())
@@ -254,6 +240,14 @@ void Pad::UpdateJoyStat()
   m_JOY_STAT.TXRDY = !m_transmit_buffer_full;
 }
 
+void Pad::TransferEvent(TickCount ticks_late)
+{
+  if (m_state == State::Transmitting)
+    DoTransfer(ticks_late);
+  else
+    DoACK();
+}
+
 void Pad::BeginTransfer()
 {
   DebugAssert(m_state == State::Idle && CanTransfer());
@@ -278,13 +272,11 @@ void Pad::BeginTransfer()
   // test in (7) will fail, and it won't send any more data. So, the transfer/interrupt must be delayed
   // until after (4) and (5) have been completed.
 
-  m_system->Synchronize();
   m_state = State::Transmitting;
-  m_ticks_remaining = GetTransferTicks();
+  m_transfer_event->SetPeriodAndSchedule(GetTransferTicks());
-  m_system->SetDowncount(m_ticks_remaining);
 }
 
-void Pad::DoTransfer()
+void Pad::DoTransfer(TickCount ticks_late)
 {
   Log_DebugPrintf("Transferring slot %d", m_JOY_CTRL.SLOT.GetValue());
 
@@ -361,11 +353,10 @@ void Pad::DoTransfer()
     const TickCount ack_timer = GetACKTicks();
     Log_DebugPrintf("Delaying ACK for %d ticks", ack_timer);
     m_state = State::WaitingForACK;
-    m_ticks_remaining += ack_timer;
+    if (ticks_late >= ack_timer)
-    if (m_ticks_remaining <= 0)
       DoACK();
     else
-      m_system->SetDowncount(m_ticks_remaining);
+      m_transfer_event->SetPeriodAndSchedule(ack_timer - ticks_late);
   }
 
   UpdateJoyStat();
@@ -395,7 +386,7 @@ void Pad::EndTransfer()
   Log_DebugPrintf("Ending transfer");
 
   m_state = State::Idle;
-  m_ticks_remaining = 0;
+  m_transfer_event->Deactivate();
 }
 
 void Pad::ResetDeviceTransferState()

src/core/pad.h

@@ -8,6 +8,7 @@
 class StateWrapper;
 
 class System;
+class TimingEvent;
 class InterruptController;
 class Controller;
 class MemoryCard;
@@ -31,8 +32,6 @@ public:
   u32 ReadRegister(u32 offset);
   void WriteRegister(u32 offset, u32 value);
 
-  void Execute(TickCount ticks);
-
 private:
   static constexpr u32 NUM_SLOTS = 2;
 
@@ -97,8 +96,9 @@ private:
 
   void SoftReset();
   void UpdateJoyStat();
+  void TransferEvent(TickCount ticks_late);
   void BeginTransfer();
-  void DoTransfer();
+  void DoTransfer(TickCount ticks_late);
   void DoACK();
   void EndTransfer();
   void ResetDeviceTransferState();
@@ -109,8 +109,8 @@ private:
   std::array<std::unique_ptr<Controller>, NUM_SLOTS> m_controllers;
   std::array<std::unique_ptr<MemoryCard>, NUM_SLOTS> m_memory_cards;
 
+  std::unique_ptr<TimingEvent> m_transfer_event;
   State m_state = State::Idle;
-  TickCount m_ticks_remaining = 0;
 
   JOY_CTRL m_JOY_CTRL = {};
   JOY_STAT m_JOY_STAT = {};

src/core/spu.cpp

@@ -1,6 +1,6 @@
 #include "spu.h"
-#include "common/log.h"
 #include "common/audio_stream.h"
+#include "common/log.h"
 #include "common/state_wrapper.h"
 #include "dma.h"
 #include "host_interface.h"
@@ -24,6 +24,8 @@ void SPU::Initialize(System* system, DMA* dma, InterruptController* interrupt_co
   m_system = system;
   m_dma = dma;
   m_interrupt_controller = interrupt_controller;
+  m_sample_event = m_system->CreateTimingEvent("SPU Sample", SYSCLK_TICKS_PER_SPU_TICK, SYSCLK_TICKS_PER_SPU_TICK,
+                                               std::bind(&SPU::Execute, this, std::placeholders::_1), false);
 }
 
 void SPU::Reset()
@@ -65,6 +67,7 @@ void SPU::Reset()
   }
 
   m_ram.fill(0);
+  UpdateEventInterval();
 }
 
 bool SPU::DoState(StateWrapper& sw)
@@ -108,7 +111,10 @@ bool SPU::DoState(StateWrapper& sw)
   sw.DoBytes(m_ram.data(), RAM_SIZE);
 
   if (sw.IsReading())
+  {
     m_system->GetHostInterface()->GetAudioStream()->EmptyBuffers();
+    UpdateEventInterval();
+  }
 
   return !sw.HasError();
 }
@@ -178,6 +184,7 @@ u16 SPU::ReadRegister(u32 offset)
 
     case 0x1F801DAE - SPU_BASE:
       // Log_DebugPrintf("SPU status register -> 0x%04X", ZeroExtend32(m_SPUCNT.bits));
+      m_sample_event->InvokeEarly();
       return m_SPUSTAT.bits;
 
     case 0x1F801DB0 - SPU_BASE:
@@ -205,7 +212,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D80 - SPU_BASE:
     {
       Log_DebugPrintf("SPU main volume left <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_main_volume_left.bits = value;
       return;
     }
@@ -213,7 +220,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D82 - SPU_BASE:
     {
       Log_DebugPrintf("SPU main volume right <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_main_volume_right.bits = value;
       return;
     }
@@ -221,7 +228,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D88 - SPU_BASE:
     {
       Log_DebugPrintf("SPU key on low <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_key_on_register = (m_key_on_register & 0xFFFF0000) | ZeroExtend32(value);
 
       u16 bits = value;
@@ -240,7 +247,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D8A - SPU_BASE:
     {
       Log_DebugPrintf("SPU key on high <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_key_on_register = (m_key_on_register & 0x0000FFFF) | (ZeroExtend32(value) << 16);
 
       u16 bits = value;
@@ -259,7 +266,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D8C - SPU_BASE:
     {
       Log_DebugPrintf("SPU key off low <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_key_on_register = (m_key_on_register & 0xFFFF0000) | ZeroExtend32(value);
 
       u16 bits = value;
@@ -278,7 +285,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D8E - SPU_BASE:
     {
       Log_DebugPrintf("SPU key off high <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_key_on_register = (m_key_on_register & 0x0000FFFF) | (ZeroExtend32(value) << 16);
 
       u16 bits = value;
@@ -296,7 +303,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
 
     case 0x1F801D90 - SPU_BASE:
     {
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_pitch_modulation_enable_register = (m_pitch_modulation_enable_register & 0xFFFF0000) | ZeroExtend32(value);
       Log_DebugPrintf("SPU pitch modulation enable register <- 0x%08X", m_pitch_modulation_enable_register);
     }
@@ -304,7 +311,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
 
     case 0x1F801D92 - SPU_BASE:
     {
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_pitch_modulation_enable_register =
         (m_pitch_modulation_enable_register & 0x0000FFFF) | (ZeroExtend32(value) << 16);
       Log_DebugPrintf("SPU pitch modulation enable register <- 0x%08X", m_pitch_modulation_enable_register);
@@ -314,7 +321,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D94 - SPU_BASE:
     {
       Log_DebugPrintf("SPU noise mode register <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_noise_mode_register = (m_noise_mode_register & 0xFFFF0000) | ZeroExtend32(value);
     }
     break;
@@ -322,7 +329,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D96 - SPU_BASE:
     {
       Log_DebugPrintf("SPU noise mode register <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_noise_mode_register = (m_noise_mode_register & 0x0000FFFF) | (ZeroExtend32(value) << 16);
     }
     break;
@@ -330,7 +337,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D98 - SPU_BASE:
     {
       Log_DebugPrintf("SPU reverb on register <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_reverb_on_register = (m_reverb_on_register & 0xFFFF0000) | ZeroExtend32(value);
     }
     break;
@@ -338,7 +345,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801D9A - SPU_BASE:
     {
       Log_DebugPrintf("SPU reverb off register <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_reverb_on_register = (m_reverb_on_register & 0x0000FFFF) | (ZeroExtend32(value) << 16);
     }
     break;
@@ -346,6 +353,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801DA4 - SPU_BASE:
     {
       Log_DebugPrintf("SPU IRQ address register <- 0x%04X", ZeroExtend32(value));
+      m_sample_event->InvokeEarly();
       m_irq_address = value;
       return;
     }
@@ -369,6 +377,8 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801DAA - SPU_BASE:
     {
       Log_DebugPrintf("SPU control register <- 0x%04X", ZeroExtend32(value));
+      m_sample_event->InvokeEarly(true);
+
       m_SPUCNT.bits = value;
       m_SPUSTAT.mode = m_SPUCNT.mode.GetValue();
       m_SPUSTAT.dma_read_write_request = m_SPUCNT.ram_transfer_mode >= RAMTransferMode::DMAWrite;
@@ -377,6 +387,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
         m_SPUSTAT.irq9_flag = false;
 
       UpdateDMARequest();
+      UpdateEventInterval();
       return;
     }
 
@@ -390,7 +401,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801DB0 - SPU_BASE:
     {
       Log_DebugPrintf("SPU left cd audio register <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_cd_audio_volume_left = value;
     }
     break;
@@ -398,7 +409,7 @@ void SPU::WriteRegister(u32 offset, u16 value)
     case 0x1F801DB2 - SPU_BASE:
     {
       Log_DebugPrintf("SPU right cd audio register <- 0x%04X", ZeroExtend32(value));
-      m_system->Synchronize();
+      m_sample_event->InvokeEarly();
       m_cd_audio_volume_right = value;
     }
     break;
@@ -424,6 +435,12 @@ u16 SPU::ReadVoiceRegister(u32 offset)
   const u32 voice_index = (offset / 0x10);   //((offset >> 4) & 0x1F);
   Assert(voice_index < 24);
 
+  if (reg_index >= 6)
+  {
+    // adsr volume needs to be updated when reading
+    m_sample_event->InvokeEarly();
+  }
+
   return m_voices[voice_index].regs.index[reg_index];
 }
 
@@ -436,7 +453,7 @@ void SPU::WriteVoiceRegister(u32 offset, u16 value)
 
   Voice& voice = m_voices[voice_index];
   if (voice.IsOn())
-    m_system->Synchronize();
+    m_sample_event->InvokeEarly();
 
   switch (reg_index)
   {
@@ -606,13 +623,103 @@ void SPU::IncrementCaptureBufferPosition()
 
 void SPU::Execute(TickCount ticks)
 {
-  TickCount num_samples = (ticks + m_ticks_carry) / SYSCLK_TICKS_PER_SPU_TICK;
+  DebugAssert(m_SPUCNT.enable || m_SPUCNT.cd_audio_enable);
+
+  u32 remaining_frames = static_cast<u32>((ticks + m_ticks_carry) / SYSCLK_TICKS_PER_SPU_TICK);
   m_ticks_carry = (ticks + m_ticks_carry) % SYSCLK_TICKS_PER_SPU_TICK;
-  if (num_samples == 0 || (!m_SPUCNT.enable && !m_SPUCNT.cd_audio_enable))
+
+  while (remaining_frames > 0)
+  {
+    AudioStream* const output_stream = m_system->GetHostInterface()->GetAudioStream();
+    s16* output_frame;
+    u32 output_frame_space;
+    output_stream->BeginWrite(&output_frame, &output_frame_space);
+
+    const u32 frames_in_this_batch = std::min(remaining_frames, output_frame_space);
+    for (u32 i = 0; i < frames_in_this_batch; i++)
+    {
+      s32 left_sum = 0;
+      s32 right_sum = 0;
+      if (m_SPUCNT.enable)
+      {
+        for (u32 voice = 0; voice < NUM_VOICES; voice++)
+        {
+          const auto [left, right] = SampleVoice(voice);
+          left_sum += left;
+          right_sum += right;
+        }
+
+        if (!m_SPUCNT.mute_n)
+        {
+          left_sum = 0;
+          right_sum = 0;
+        }
+      }
+
+      // Mix in CD audio.
+      s16 cd_audio_left;
+      s16 cd_audio_right;
+      if (!m_cd_audio_buffer.IsEmpty())
+      {
+        cd_audio_left = m_cd_audio_buffer.Pop();
+        cd_audio_right = m_cd_audio_buffer.Pop();
+        if (m_SPUCNT.cd_audio_enable)
+        {
+          left_sum += ApplyVolume(s32(cd_audio_left), m_cd_audio_volume_left);
+          right_sum += ApplyVolume(s32(cd_audio_right), m_cd_audio_volume_right);
+        }
+      }
+      else
+      {
+        cd_audio_left = 0;
+        cd_audio_right = 0;
+      }
+
+      // Apply main volume before clamping.
+      *(output_frame++) = Clamp16(ApplyVolume(left_sum, m_main_volume_left.GetVolume()));
+      *(output_frame++) = Clamp16(ApplyVolume(right_sum, m_main_volume_right.GetVolume()));
+
+      // Write to capture buffers.
+      WriteToCaptureBuffer(0, cd_audio_left);
+      WriteToCaptureBuffer(1, cd_audio_right);
+      WriteToCaptureBuffer(2, Clamp16(m_voices[1].last_amplitude));
+      WriteToCaptureBuffer(3, Clamp16(m_voices[3].last_amplitude));
+      IncrementCaptureBufferPosition();
+    }
+
+    output_stream->EndWrite(frames_in_this_batch);
+    remaining_frames -= frames_in_this_batch;
+  }
+}
+
+void SPU::UpdateEventInterval()
+{
+  if (!m_SPUCNT.enable && !m_SPUCNT.cd_audio_enable)
+  {
+    m_sample_event->Deactivate();
+    return;
+  }
+
+  // Don't generate more than the audio buffer since in a single slice, otherwise we'll both overflow the buffers when
+  // we do write it, and the audio thread will underflow since it won't have enough data it the game isn't messing with
+  // the SPU state.
+  const u32 max_slice_frames = m_system->GetHostInterface()->GetAudioStream()->GetBufferSize();
+
+  // TODO: Make this predict how long until the interrupt will be hit instead...
+  const u32 interval = m_SPUCNT.irq9_enable ? 1 : max_slice_frames;
+  const TickCount interval_ticks = static_cast<TickCount>(interval) * SYSCLK_TICKS_PER_SPU_TICK;
+  if (m_sample_event->IsActive() && m_sample_event->GetInterval() == interval_ticks)
     return;
 
-  for (TickCount i = 0; i < num_samples; i++)
+  // Ensure all pending ticks have been executed, since we won't get them back after rescheduling.
-    GenerateSample();
+  m_sample_event->InvokeEarly(true);
+  m_sample_event->SetInterval(interval_ticks);
+  m_sample_event->Schedule(interval_ticks - m_ticks_carry);
+}
+
+void SPU::GeneratePendingSamples()
+{
+  m_sample_event->InvokeEarly();
 }
 
 void SPU::Voice::KeyOn()
@@ -952,80 +1059,22 @@ std::tuple<s32, s32> SPU::SampleVoice(u32 voice_index)
   return std::make_tuple(left, right);
 }
 
-void SPU::EnsureCDAudioSpace(u32 num_samples)
+void SPU::EnsureCDAudioSpace(u32 remaining_frames)
 {
-  if (m_cd_audio_buffer.GetSpace() < (num_samples * 2))
+  if (m_cd_audio_buffer.IsEmpty())
   {
-    Log_WarningPrintf("SPU CD Audio buffer overflow - writing %u samples with %u samples space", num_samples,
+    // we want the audio to start playing at the right point, not a few cycles early, otherwise this'll cause sync issues.
+    m_sample_event->InvokeEarly();
+  }
+
+  if (m_cd_audio_buffer.GetSpace() < (remaining_frames * 2))
+  {
+    Log_WarningPrintf("SPU CD Audio buffer overflow - writing %u samples with %u samples space", remaining_frames,
                       m_cd_audio_buffer.GetSpace() / 2);
-    m_cd_audio_buffer.Remove((num_samples * 2) - m_cd_audio_buffer.GetSpace());
+    m_cd_audio_buffer.Remove((remaining_frames * 2) - m_cd_audio_buffer.GetSpace());
   }
 }
 
-void SPU::GenerateSample()
-{
-  s32 left_sum = 0;
-  s32 right_sum = 0;
-  if (m_SPUCNT.enable)
-  {
-    for (u32 i = 0; i < NUM_VOICES; i++)
-    {
-      const auto [left, right] = SampleVoice(i);
-      left_sum += left;
-      right_sum += right;
-    }
-
-    if (!m_SPUCNT.mute_n)
-    {
-      left_sum = 0;
-      right_sum = 0;
-    }
-  }
-
-  // Mix in CD audio.
-  s16 cd_audio_left;
-  s16 cd_audio_right;
-  if (!m_cd_audio_buffer.IsEmpty())
-  {
-    cd_audio_left = m_cd_audio_buffer.Pop();
-    cd_audio_right = m_cd_audio_buffer.Pop();
-    if (m_SPUCNT.cd_audio_enable)
-    {
-      left_sum += ApplyVolume(s32(cd_audio_left), m_cd_audio_volume_left);
-      right_sum += ApplyVolume(s32(cd_audio_right), m_cd_audio_volume_right);
-    }
-  }
-  else
-  {
-    cd_audio_left = 0;
-    cd_audio_right = 0;
-  }
-
-  // Apply main volume before clamping.
-  std::array<AudioStream::SampleType, 2> out_samples;
-  out_samples[0] = Clamp16(ApplyVolume(left_sum, m_main_volume_left.GetVolume()));
-  out_samples[1] = Clamp16(ApplyVolume(right_sum, m_main_volume_right.GetVolume()));
-  m_system->GetHostInterface()->GetAudioStream()->WriteSamples(out_samples.data(), 1);
-
-  // Write to capture buffers.
-  WriteToCaptureBuffer(0, cd_audio_left);
-  WriteToCaptureBuffer(1, cd_audio_right);
-  WriteToCaptureBuffer(2, Clamp16(m_voices[1].last_amplitude));
-  WriteToCaptureBuffer(3, Clamp16(m_voices[3].last_amplitude));
-  IncrementCaptureBufferPosition();
-
-#if 0
-  static FILE* fp = nullptr;
-  if (!fp)
-    fp = std::fopen("D:\\spu.raw", "wb");
-  if (fp)
-  {
-    std::fwrite(out_samples.data(), sizeof(AudioStream::SampleType), 2, fp);
-    std::fflush(fp);
-  }
-#endif
-}
-
 void SPU::DrawDebugStateWindow()
 {
   static const ImVec4 active_color{1.0f, 1.0f, 1.0f, 1.0f};

src/core/spu.h

@@ -3,11 +3,12 @@
 #include "common/fifo_queue.h"
 #include "types.h"
 #include <array>
+#include <memory>
 
-class AudioStream;
 class StateWrapper;
 
 class System;
+class TimingEvent;
 class DMA;
 class InterruptController;
 
@@ -27,8 +28,6 @@ public:
   void DMARead(u32* words, u32 word_count);
   void DMAWrite(const u32* words, u32 word_count);
 
-  void Execute(TickCount ticks);
-
   // Render statistics debug window.
   void DrawDebugStateWindow();
 
@@ -40,6 +39,9 @@ public:
   }
   void EnsureCDAudioSpace(u32 num_samples);
 
+  // Executes the SPU, generating any pending samples.
+  void GeneratePendingSamples();
+
 private:
   static constexpr u32 RAM_SIZE = 512 * 1024;
   static constexpr u32 RAM_MASK = RAM_SIZE - 1;
@@ -282,11 +284,13 @@ private:
 
   void ReadADPCMBlock(u16 address, ADPCMBlock* block);
   std::tuple<s32, s32> SampleVoice(u32 voice_index);
-  void GenerateSample();
+  void Execute(TickCount ticks);
+  void UpdateEventInterval();
 
   System* m_system = nullptr;
   DMA* m_dma = nullptr;
   InterruptController* m_interrupt_controller = nullptr;
+  std::unique_ptr<TimingEvent> m_sample_event = nullptr;
 
   SPUCNT m_SPUCNT = {};
   SPUSTAT m_SPUSTAT = {};

src/core/system.cpp

@@ -40,7 +40,11 @@ System::System(HostInterface* host_interface) : m_host_interface(host_interface)
   m_cpu_execution_mode = host_interface->m_settings.cpu_execution_mode;
 }
 
-System::~System() = default;
+System::~System()
+{
+  // we have to explicitly destroy components because they can deregister events
+  DestroyComponents();
+}
 
 std::unique_ptr<System> System::Create(HostInterface* host_interface)
 {
@@ -56,7 +60,7 @@ bool System::RecreateGPU(GPURenderer renderer)
   // save current state
   std::unique_ptr<ByteStream> state_stream = ByteStream_CreateGrowableMemoryStream();
   StateWrapper sw(state_stream.get(), StateWrapper::Mode::Write);
-  const bool state_valid = m_gpu->DoState(sw);
+  const bool state_valid = m_gpu->DoState(sw) && DoEventsState(sw);
   if (!state_valid)
     Log_ErrorPrintf("Failed to save old GPU state when switching renderers");
 
@@ -73,6 +77,7 @@ bool System::RecreateGPU(GPURenderer renderer)
     state_stream->SeekAbsolute(0);
     sw.SetMode(StateWrapper::Mode::Read);
     m_gpu->DoState(sw);
+    DoEventsState(sw);
   }
 
   return true;
@@ -188,11 +193,26 @@ void System::InitializeComponents()
 
   m_cdrom->Initialize(this, m_dma.get(), m_interrupt_controller.get(), m_spu.get());
   m_pad->Initialize(this, m_interrupt_controller.get());
-  m_timers->Initialize(this, m_interrupt_controller.get());
+  m_timers->Initialize(this, m_interrupt_controller.get(), m_gpu.get());
   m_spu->Initialize(this, m_dma.get(), m_interrupt_controller.get());
   m_mdec->Initialize(this, m_dma.get());
 }
 
+void System::DestroyComponents()
+{
+  m_mdec.reset();
+  m_spu.reset();
+  m_timers.reset();
+  m_pad.reset();
+  m_cdrom.reset();
+  m_gpu.reset();
+  m_interrupt_controller.reset();
+  m_dma.reset();
+  m_bus.reset();
+  m_cpu_code_cache.reset();
+  m_cpu.reset();
+}
+
 bool System::CreateGPU(GPURenderer renderer)
 {
   switch (renderer)
@@ -230,6 +250,7 @@ bool System::CreateGPU(GPURenderer renderer)
 
   m_bus->SetGPU(m_gpu.get());
   m_dma->SetGPU(m_gpu.get());
+  m_timers->SetGPU(m_gpu.get());
   return true;
 }
 
@@ -298,6 +319,9 @@ bool System::DoState(StateWrapper& sw)
   if (!sw.DoMarker("SIO") || !m_sio->DoState(sw))
     return false;
 
+  if (!sw.DoMarker("Events") || !DoEventsState(sw))
+    return false;
+
   return !sw.HasError();
 }
 
@@ -318,6 +342,7 @@ void System::Reset()
   m_frame_number = 1;
   m_internal_frame_number = 0;
   m_global_tick_counter = 0;
+  m_last_event_run_time = 0;
 }
 
 bool System::LoadState(ByteStream* state)
@@ -335,23 +360,28 @@ bool System::SaveState(ByteStream* state)
 void System::RunFrame()
 {
   // Duplicated to avoid branch in the while loop, as the downcount can be quite low at times.
-  u32 current_frame_number = m_frame_number;
+  m_frame_done = false;
   if (m_cpu_execution_mode == CPUExecutionMode::Interpreter)
   {
-    while (current_frame_number == m_frame_number)
+    do
     {
+      UpdateCPUDowncount();
       m_cpu->Execute();
-      Synchronize();
+      RunEvents();
-    }
+    } while (!m_frame_done);
   }
   else
   {
-    while (current_frame_number == m_frame_number)
+    do
     {
+      UpdateCPUDowncount();
       m_cpu_code_cache->Execute();
-      Synchronize();
+      RunEvents();
-    }
+    } while (!m_frame_done);
   }
+
+  // Generate any pending samples from the SPU before sleeping, this way we reduce the chances of underruns.
+  m_spu->GeneratePendingSamples();
 }
 
 bool System::LoadEXE(const char* filename, std::vector<u8>& bios_image)
@@ -438,34 +468,11 @@ bool System::SetExpansionROM(const char* filename)
   return true;
 }
 
-void System::Synchronize()
-{
-  const TickCount pending_ticks = m_cpu->GetPendingTicks();
-  if (pending_ticks == 0)
-    return;
-
-  m_cpu->ResetPendingTicks();
-  m_cpu->ResetDowncount();
-
-  m_global_tick_counter += static_cast<u32>(pending_ticks);
-
-  m_gpu->Execute(pending_ticks);
-  m_timers->Execute(pending_ticks);
-  m_cdrom->Execute(pending_ticks);
-  m_pad->Execute(pending_ticks);
-  m_spu->Execute(pending_ticks);
-  m_mdec->Execute(pending_ticks);
-  m_dma->Execute(pending_ticks);
-}
-
-void System::SetDowncount(TickCount downcount)
-{
-  m_cpu->SetDowncount(downcount);
-}
-
 void System::StallCPU(TickCount ticks)
 {
   m_cpu->AddPendingTicks(ticks);
+  if (m_cpu->GetPendingTicks() >= m_cpu->GetDowncount() && !m_running_events)
+    RunEvents();
 }
 
 Controller* System::GetController(u32 slot) const
@@ -530,6 +537,202 @@ void System::RemoveMedia()
   m_cdrom->RemoveMedia();
 }
 
+std::unique_ptr<TimingEvent> System::CreateTimingEvent(std::string name, TickCount period, TickCount interval,
+                                                       TimingEventCallback callback, bool activate)
+{
+  std::unique_ptr<TimingEvent> event =
+    std::make_unique<TimingEvent>(this, std::move(name), period, interval, std::move(callback));
+  if (activate)
+    event->Activate();
+
+  return event;
+}
+
+static bool CompareEvents(const TimingEvent* lhs, const TimingEvent* rhs)
+{
+  return lhs->GetDowncount() > rhs->GetDowncount();
+}
+
+void System::AddActiveEvent(TimingEvent* event)
+{
+  m_events.push_back(event);
+  if (!m_running_events)
+  {
+    std::push_heap(m_events.begin(), m_events.end(), CompareEvents);
+    if (!m_frame_done)
+      UpdateCPUDowncount();
+  }
+  else
+  {
+    m_events_need_sorting = true;
+  }
+}
+
+void System::RemoveActiveEvent(TimingEvent* event)
+{
+  auto iter = std::find_if(m_events.begin(), m_events.end(), [event](const auto& it) { return event == it; });
+  if (iter == m_events.end())
+  {
+    Panic("Attempt to remove inactive event");
+    return;
+  }
+
+  m_events.erase(iter);
+  if (!m_running_events)
+  {
+    std::make_heap(m_events.begin(), m_events.end(), CompareEvents);
+    if (!m_events.empty() && !m_frame_done)
+      UpdateCPUDowncount();
+  }
+  else
+  {
+    m_events_need_sorting = true;
+  }
+}
+
+void System::SortEvents()
+{
+  if (!m_running_events)
+  {
+    std::make_heap(m_events.begin(), m_events.end(), CompareEvents);
+    if (!m_frame_done)
+      UpdateCPUDowncount();
+  }
+  else
+  {
+    m_events_need_sorting = true;
+  }
+}
+
+void System::RunEvents()
+{
+  DebugAssert(!m_running_events && !m_events.empty());
+
+  const TickCount pending_ticks = m_cpu->GetPendingTicks();
+  m_global_tick_counter += static_cast<u32>(pending_ticks);
+  m_cpu->ResetPendingTicks();
+
+  TickCount time = static_cast<TickCount>(m_global_tick_counter - m_last_event_run_time);
+  m_running_events = true;
+  m_last_event_run_time = m_global_tick_counter;
+
+  // Apply downcount to all events.
+  // This will result in a negative downcount for those events which are late.
+  for (TimingEvent* evt : m_events)
+  {
+    evt->m_downcount -= time;
+    evt->m_time_since_last_run += time;
+  }
+
+  // Now we can actually run the callbacks.
+  while (m_events.front()->GetDowncount() <= 0)
+  {
+    TimingEvent* evt = m_events.front();
+    const TickCount ticks_late = -evt->m_downcount;
+    std::pop_heap(m_events.begin(), m_events.end(), CompareEvents);
+
+    // Factor late time into the time for the next invocation.
+    const TickCount ticks_to_execute = evt->m_time_since_last_run;
+    evt->m_downcount += evt->m_interval;
+    evt->m_time_since_last_run = 0;
+
+    // The cycles_late is only an indicator, it doesn't modify the cycles to execute.
+    evt->m_callback(ticks_to_execute, ticks_late);
+
+    // Place it in the appropriate position in the queue.
+    if (m_events_need_sorting)
+    {
+      // Another event may have been changed by this event, or the interval/downcount changed.
+      std::make_heap(m_events.begin(), m_events.end(), CompareEvents);
+      m_events_need_sorting = false;
+    }
+    else
+    {
+      // Keep the event list in a heap. The event we just serviced will be in the last place,
+      // so we can use push_here instead of make_heap, which should be faster.
+      std::push_heap(m_events.begin(), m_events.end(), CompareEvents);
+    }
+  }
+
+  m_running_events = false;
+  m_cpu->SetDowncount(m_events.front()->GetDowncount());
+}
+
+void System::UpdateCPUDowncount()
+{
+  m_cpu->SetDowncount(m_events[0]->GetDowncount());
+}
+
+bool System::DoEventsState(StateWrapper& sw)
+{
+  if (sw.IsReading())
+  {
+    // Load timestamps for the clock events.
+    // Any oneshot events should be recreated by the load state method, so we can fix up their times here.
+    u32 event_count = 0;
+    sw.Do(&event_count);
+
+    for (u32 i = 0; i < event_count; i++)
+    {
+      std::string event_name;
+      TickCount downcount, time_since_last_run, period, interval;
+      sw.Do(&event_name);
+      sw.Do(&downcount);
+      sw.Do(&time_since_last_run);
+      sw.Do(&period);
+      sw.Do(&interval);
+      if (sw.HasError())
+        return false;
+
+      TimingEvent* event = FindActiveEvent(event_name.c_str());
+      if (!event)
+      {
+        Log_WarningPrintf("Save state has event '%s', but couldn't find this event when loading.", event_name.c_str());
+        continue;
+      }
+
+      // Using reschedule is safe here since we call sort afterwards.
+      event->m_downcount = downcount;
+      event->m_time_since_last_run = time_since_last_run;
+      event->m_period = period;
+      event->m_interval = interval;
+    }
+
+    sw.Do(&m_last_event_run_time);
+
+    Log_DevPrintf("Loaded %u events from save state.", event_count);
+    SortEvents();
+  }
+  else
+  {
+    u32 event_count = static_cast<u32>(m_events.size());
+    sw.Do(&event_count);
+
+    for (TimingEvent* evt : m_events)
+    {
+      sw.Do(&evt->m_name);
+      sw.Do(&evt->m_downcount);
+      sw.Do(&evt->m_time_since_last_run);
+      sw.Do(&evt->m_period);
+      sw.Do(&evt->m_interval);
+    }
+
+    sw.Do(&m_last_event_run_time);
+
+    Log_DevPrintf("Wrote %u events to save state.", event_count);
+  }
+
+  return !sw.HasError();
+}
+
+TimingEvent* System::FindActiveEvent(const char* name)
+{
+  auto iter =
+    std::find_if(m_events.begin(), m_events.end(), [&name](auto& ev) { return ev->GetName().compare(name) == 0; });
+
+  return (iter != m_events.end()) ? *iter : nullptr;
+}
+
 void System::UpdateRunningGame(const char* path, CDImage* image)
 {
   m_running_game_path.clear();

src/core/system.h

@@ -1,5 +1,6 @@
 #pragma once
 #include "host_interface.h"
+#include "timing_event.h"
 #include "types.h"
 #include <memory>
 #include <optional>
@@ -28,6 +29,8 @@ class SIO;
 
 class System
 {
+  friend TimingEvent;
+
 public:
   ~System();
 
@@ -52,7 +55,11 @@ public:
   u32 GetFrameNumber() const { return m_frame_number; }
   u32 GetInternalFrameNumber() const { return m_internal_frame_number; }
   u32 GetGlobalTickCounter() const { return m_global_tick_counter; }
-  void IncrementFrameNumber() { m_frame_number++; }
+  void IncrementFrameNumber()
+  {
+    m_frame_number++;
+    m_frame_done = true;
+  }
   void IncrementInternalFrameNumber() { m_internal_frame_number++; }
 
   const Settings& GetSettings() { return m_host_interface->GetSettings(); }
@@ -78,9 +85,6 @@ public:
   bool LoadEXE(const char* filename, std::vector<u8>& bios_image);
   bool SetExpansionROM(const char* filename);
 
-  void SetDowncount(TickCount downcount);
-  void Synchronize();
-
   // Adds ticks to the global tick counter, simulating the CPU being stalled.
   void StallCPU(TickCount ticks);
 
@@ -94,6 +98,12 @@ public:
   bool InsertMedia(const char* path);
   void RemoveMedia();
 
+  /// Creates a new event.
+  std::unique_ptr<TimingEvent> CreateTimingEvent(std::string name, TickCount period, TickCount interval,
+                                                 TimingEventCallback callback, bool activate);
+
+  bool RUNNING_EVENTS() const { return m_running_events; }
+
 private:
   System(HostInterface* host_interface);
 
@@ -101,6 +111,33 @@ private:
   bool CreateGPU(GPURenderer renderer);
 
   void InitializeComponents();
+  void DestroyComponents();
+
+  // Active event management
+  void AddActiveEvent(TimingEvent* event);
+  void RemoveActiveEvent(TimingEvent* event);
+  void SortEvents();
+
+  // Runs any pending events. Call when CPU downcount is zero.
+  void RunEvents();
+
+  // Updates the downcount of the CPU (event scheduling).
+  void UpdateCPUDowncount();
+
+  bool DoEventsState(StateWrapper& sw);
+
+  // Event lookup, use with care.
+  // If you modify an event, call SortEvents afterwards.
+  TimingEvent* FindActiveEvent(const char* name);
+
+  // Event enumeration, use with care.
+  // Don't remove an event while enumerating the list, as it will invalidate the iterator.
+  template<typename T>
+  void EnumerateActiveEvents(T callback) const
+  {
+    for (const TimingEvent* ev : m_events)
+      callback(ev);
+  }
 
   void UpdateRunningGame(const char* path, CDImage* image);
 
@@ -123,6 +160,12 @@ private:
   u32 m_internal_frame_number = 1;
   u32 m_global_tick_counter = 0;
 
+  std::vector<TimingEvent*> m_events;
+  u32 m_last_event_run_time = 0;
+  bool m_running_events = false;
+  bool m_events_need_sorting = false;
+  bool m_frame_done = false;
+
   std::string m_running_game_path;
   std::string m_running_game_code;
   std::string m_running_game_title;

src/core/timers.cpp

@@ -1,6 +1,7 @@
 #include "timers.h"
 #include "common/log.h"
 #include "common/state_wrapper.h"
+#include "gpu.h"
 #include "interrupt_controller.h"
 #include "system.h"
 #include <imgui.h>
@@ -10,10 +11,13 @@ Timers::Timers() = default;
 
 Timers::~Timers() = default;
 
-void Timers::Initialize(System* system, InterruptController* interrupt_controller)
+void Timers::Initialize(System* system, InterruptController* interrupt_controller, GPU* gpu)
 {
   m_system = system;
   m_interrupt_controller = interrupt_controller;
+  m_gpu = gpu;
+  m_sysclk_event = system->CreateTimingEvent("Timer SysClk Interrupt", 1, 1,
+                                             std::bind(&Timers::AddSysClkTicks, this, std::placeholders::_1), false);
 }
 
 void Timers::Reset()
@@ -30,6 +34,7 @@ void Timers::Reset()
   }
 
   m_sysclk_div_8_carry = 0;
+  UpdateSysClkEvent();
 }
 
 bool Timers::DoState(StateWrapper& sw)
@@ -47,6 +52,10 @@ bool Timers::DoState(StateWrapper& sw)
   }
 
   sw.Do(&m_sysclk_div_8_carry);
+
+  if (sw.IsReading())
+    UpdateSysClkEvent();
+
   return !sw.HasError();
 }
 
@@ -88,12 +97,12 @@ void Timers::AddTicks(u32 timer, TickCount count)
   bool interrupt_request = false;
   if (cs.counter >= cs.target && old_counter < cs.target)
   {
-    interrupt_request = true;
+    interrupt_request |= cs.mode.irq_at_target;
     cs.mode.reached_target = true;
   }
   if (cs.counter >= 0xFFFF)
   {
-    interrupt_request = true;
+    interrupt_request |= cs.mode.irq_on_overflow;
     cs.mode.reached_overflow = true;
   }
 
@@ -126,7 +135,7 @@ void Timers::AddTicks(u32 timer, TickCount count)
   }
 }
 
-void Timers::Execute(TickCount sysclk_ticks)
+void Timers::AddSysClkTicks(TickCount sysclk_ticks)
 {
   if (!m_states[0].external_counting_enabled && m_states[0].counting_enabled)
     AddTicks(0, sysclk_ticks);
@@ -143,7 +152,7 @@ void Timers::Execute(TickCount sysclk_ticks)
     AddTicks(2, sysclk_ticks);
   }
 
-  UpdateDowncount();
+  UpdateSysClkEvent();
 }
 
 u32 Timers::ReadRegister(u32 offset)
@@ -157,13 +166,28 @@ u32 Timers::ReadRegister(u32 offset)
   {
     case 0x00:
     {
-      m_system->Synchronize();
+      if (timer_index < 2)
+      {
+        // timers 0/1 depend on the GPU
+        if (cs.external_counting_enabled)
+          m_gpu->Synchronize();
+      }
+
+      m_sysclk_event->InvokeEarly();
+
       return cs.counter;
     }
 
     case 0x04:
     {
-      m_system->Synchronize();
+      if (timer_index < 2)
+      {
+        // timers 0/1 depend on the GPU
+        if (cs.external_counting_enabled)
+          m_gpu->Synchronize();
+      }
+
+      m_sysclk_event->InvokeEarly();
 
       const u32 bits = cs.mode.bits;
       cs.mode.reached_overflow = false;
@@ -192,7 +216,7 @@ void Timers::WriteRegister(u32 offset, u32 value)
     case 0x00:
     {
       Log_DebugPrintf("Timer %u write counter %u", timer_index, value);
-      m_system->Synchronize();
+      m_sysclk_event->InvokeEarly();
       cs.counter = value & u32(0xFFFF);
     }
     break;
@@ -200,7 +224,7 @@ void Timers::WriteRegister(u32 offset, u32 value)
     case 0x04:
     {
       Log_DebugPrintf("Timer %u write mode register 0x%04X", timer_index, value);
-      m_system->Synchronize();
+      m_sysclk_event->InvokeEarly();
       cs.mode.bits = value & u32(0x1FFF);
       cs.use_external_clock = (cs.mode.clock_source & (timer_index == 2 ? 2 : 1)) != 0;
       cs.counter = 0;
@@ -210,13 +234,14 @@ void Timers::WriteRegister(u32 offset, u32 value)
 
       UpdateCountingEnabled(cs);
       UpdateIRQ(timer_index);
+      UpdateSysClkEvent();
     }
     break;
 
     case 0x08:
     {
       Log_DebugPrintf("Timer %u write target 0x%04X", timer_index, ZeroExtend32(Truncate16(value)));
-      m_system->Synchronize();
+      m_sysclk_event->InvokeEarly();
       cs.target = value & u32(0xFFFF);
     }
     break;
@@ -267,16 +292,19 @@ void Timers::UpdateIRQ(u32 index)
     static_cast<InterruptController::IRQ>(static_cast<u32>(InterruptController::IRQ::TMR0) + index));
 }
 
-void Timers::UpdateDowncount()
+TickCount Timers::GetTicksUntilNextInterrupt() const
 {
   TickCount min_ticks = std::numeric_limits<TickCount>::max();
   for (u32 i = 0; i < NUM_TIMERS; i++)
   {
-    CounterState& cs = m_states[i];
+    const CounterState& cs = m_states[i];
-    if (!cs.counting_enabled || (i < 2 && cs.external_counting_enabled))
+    if (!cs.counting_enabled || (i < 2 && cs.external_counting_enabled) ||
+        (!cs.mode.irq_at_target && !cs.mode.irq_on_overflow))
+    {
       continue;
+    }
 
-    TickCount min_ticks_for_this_timer = min_ticks;
+    TickCount min_ticks_for_this_timer = std::numeric_limits<TickCount>::max();
     if (cs.mode.irq_at_target && cs.counter < cs.target)
       min_ticks_for_this_timer = static_cast<TickCount>(cs.target - cs.counter);
     if (cs.mode.irq_on_overflow && cs.counter < cs.target)
@@ -288,7 +316,17 @@ void Timers::UpdateDowncount()
     min_ticks = std::min(min_ticks, min_ticks_for_this_timer);
   }
 
-  m_system->SetDowncount(min_ticks);
+  return min_ticks;
+}
+
+void Timers::UpdateSysClkEvent()
+{
+  // Still update once every 100ms. If we get polled we'll execute sooner.
+  const TickCount ticks = GetTicksUntilNextInterrupt();
+  if (ticks == std::numeric_limits<TickCount>::max())
+    m_sysclk_event->Schedule(MAX_SLICE_SIZE);
+  else
+    m_sysclk_event->Schedule(ticks);
 }
 
 void Timers::DrawDebugStateWindow()

src/core/timers.h

@@ -2,11 +2,14 @@
 #include "common/bitfield.h"
 #include "types.h"
 #include <array>
+#include <memory>
 
 class StateWrapper;
 
 class System;
+class TimingEvent;
 class InterruptController;
+class GPU;
 
 class Timers
 {
@@ -14,7 +17,7 @@ public:
   Timers();
   ~Timers();
 
-  void Initialize(System* system, InterruptController* interrupt_controller);
+  void Initialize(System* system, InterruptController* interrupt_controller, GPU* gpu);
   void Reset();
   bool DoState(StateWrapper& sw);
 
@@ -25,11 +28,13 @@ public:
   // dot clock/hblank/sysclk div 8
   bool IsUsingExternalClock(u32 timer) const { return m_states[timer].external_counting_enabled; }
   void AddTicks(u32 timer, TickCount ticks);
-  void Execute(TickCount sysclk_ticks);
 
   u32 ReadRegister(u32 offset);
   void WriteRegister(u32 offset, u32 value);
 
+  // changing interfaces
+  void SetGPU(GPU* gpu) { m_gpu = gpu; }
+
 private:
   static constexpr u32 NUM_TIMERS = 3;
 
@@ -73,10 +78,15 @@ private:
   void UpdateCountingEnabled(CounterState& cs);
   void UpdateIRQ(u32 index);
 
-  void UpdateDowncount();
+  void AddSysClkTicks(TickCount sysclk_ticks);
+
+  TickCount GetTicksUntilNextInterrupt() const;
+  void UpdateSysClkEvent();
 
   System* m_system = nullptr;
   InterruptController* m_interrupt_controller = nullptr;
+  GPU* m_gpu = nullptr;
+  std::unique_ptr<TimingEvent> m_sysclk_event = nullptr;
 
   std::array<CounterState, NUM_TIMERS> m_states{};
   u32 m_sysclk_div_8_carry = 0;   // partial ticks for timer 3 with sysclk/8

src/core/timing_event.cpp

@@ -0,0 +1,130 @@
+#include "timing_event.h"
+#include "common/assert.h"
+#include "cpu_core.h"
+#include "system.h"
+
+TimingEvent::TimingEvent(System* system, std::string name, TickCount period, TickCount interval,
+                         TimingEventCallback callback)
+  : m_downcount(interval), m_time_since_last_run(0), m_period(period), m_interval(interval),
+    m_callback(std::move(callback)), m_system(system), m_name(std::move(name)), m_active(false)
+{
+}
+
+TimingEvent::~TimingEvent()
+{
+  if (m_active)
+    m_system->RemoveActiveEvent(this);
+}
+
+TickCount TimingEvent::GetTicksSinceLastExecution() const
+{
+  return m_system->m_cpu->GetPendingTicks() + m_time_since_last_run;
+}
+
+TickCount TimingEvent::GetTicksUntilNextExecution() const
+{
+  return std::max(m_downcount - m_system->m_cpu->GetPendingTicks(), static_cast<TickCount>(0));
+}
+
+void TimingEvent::Schedule(TickCount ticks)
+{
+  m_downcount = ticks;
+  m_time_since_last_run = 0;
+
+  // Factor in partial time if this was rescheduled outside of an event handler. Say, an MMIO write.
+  if (!m_system->m_running_events)
+  {
+    const TickCount pending_ticks = m_system->m_cpu->GetPendingTicks();
+    m_downcount += pending_ticks;
+    m_time_since_last_run -= pending_ticks;
+  }
+
+  if (m_active)
+  {
+    // If this is a call from an IO handler for example, re-sort the event queue.
+    m_system->SortEvents();
+  }
+  else
+  {
+    m_active = true;
+    m_system->AddActiveEvent(this);
+  }
+}
+
+void TimingEvent::SetIntervalAndSchedule(TickCount ticks)
+{
+  SetInterval(ticks);
+  Schedule(ticks);
+}
+
+void TimingEvent::SetPeriodAndSchedule(TickCount ticks)
+{
+  SetPeriod(ticks);
+  SetInterval(ticks);
+  Schedule(ticks);
+}
+
+void TimingEvent::Reset()
+{
+  if (!m_active)
+    return;
+
+  m_downcount = m_interval;
+  m_time_since_last_run = 0;
+  m_system->SortEvents();
+}
+
+void TimingEvent::InvokeEarly(bool force /* = false */)
+{
+  if (!m_active)
+    return;
+
+  const TickCount pending_ticks = m_system->m_running_events ? 0 : m_system->m_cpu->GetPendingTicks();
+  const TickCount ticks_to_execute = m_time_since_last_run + pending_ticks;
+  if (!force && ticks_to_execute < m_period)
+    return;
+
+  m_downcount = pending_ticks + m_interval;
+  m_time_since_last_run -= ticks_to_execute;
+  m_callback(ticks_to_execute, 0);
+
+  // Since we've changed the downcount, we need to re-sort the events.
+  m_system->SortEvents();
+}
+
+void TimingEvent::Activate()
+{
+  if (m_active)
+    return;
+
+  // leave the downcount intact
+  const TickCount pending_ticks = m_system->m_running_events ? 0 : m_system->m_cpu->GetPendingTicks();
+  m_downcount += pending_ticks;
+  m_time_since_last_run -= pending_ticks;
+
+  m_active = true;
+  m_system->AddActiveEvent(this);
+}
+
+void TimingEvent::Deactivate()
+{
+  if (!m_active)
+    return;
+
+  const TickCount pending_ticks = m_system->m_running_events ? 0 : m_system->m_cpu->GetPendingTicks();
+  m_downcount -= pending_ticks;
+  m_time_since_last_run += pending_ticks;
+
+  m_active = false;
+  m_system->RemoveActiveEvent(this);
+}
+
+void TimingEvent::SetDowncount(TickCount downcount)
+{
+  const TickCount pending_ticks = m_system->m_running_events ? 0 : m_system->m_cpu->GetPendingTicks();
+  m_downcount = downcount + pending_ticks;
+  m_time_since_last_run = -pending_ticks;
+
+  if (m_active)
+    m_system->SortEvents();
+}

src/core/timing_event.h

@@ -0,0 +1,76 @@
+#pragma once
+#include <functional>
+#include <memory>
+#include <vector>
+
+#include "types.h"
+
+class System;
+class TimingEvent;
+
+// Event callback type. Second parameter is the number of cycles the event was executed "late".
+using TimingEventCallback = std::function<void(TickCount ticks, TickCount ticks_late)>;
+
+class TimingEvent
+{
+  friend System;
+
+public:
+  TimingEvent(System* system, std::string name, TickCount period, TickCount interval, TimingEventCallback callback);
+  ~TimingEvent();
+
+  System* GetSystem() const { return m_system; }
+  const std::string& GetName() const { return m_name; }
+  bool IsActive() const { return m_active; }
+
+  // Returns the number of ticks between each event.
+  TickCount GetPeriod() const { return m_period; }
+  TickCount GetInterval() const { return m_interval; }
+
+  TickCount GetDowncount() const { return m_downcount; }
+
+  // Includes pending time.
+  TickCount GetTicksSinceLastExecution() const;
+  TickCount GetTicksUntilNextExecution() const;
+
+  void Schedule(TickCount ticks);
+  void SetIntervalAndSchedule(TickCount ticks);
+  void SetPeriodAndSchedule(TickCount ticks);
+
+  void Reset();
+
+  // Services the event with the current accmulated time. If force is set, when not enough time is pending to
+  // simulate a single cycle, the callback will still be invoked, otherwise it won't be.
+  void InvokeEarly(bool force = false);
+
+  // Deactivates the event, preventing it from firing again.
+  // Do not call within a callback, return Deactivate instead.
+  void Activate();
+  void Deactivate();
+
+  ALWAYS_INLINE void SetState(bool active)
+  {
+    if (active)
+      Activate();
+    else
+      Deactivate();
+  }
+
+  // Directly alters the downcount of the event.
+  void SetDowncount(TickCount downcount);
+
+  // Directly alters the interval of the event.
+  void SetInterval(TickCount interval) { m_interval = interval; }
+  void SetPeriod(TickCount period) { m_period = period; }
+
+private:
+  TickCount m_downcount;
+  TickCount m_time_since_last_run;
+  TickCount m_period;
+  TickCount m_interval;
+
+  TimingEventCallback m_callback;
+  System* m_system;
+  std::string m_name;
+  bool m_active;
+};