System: Implement CPU overclocking [SAVEVERSION+]

Partial credit to @CookiePLMonster as well.

src/core/cdrom.cpp

@@ -298,6 +298,13 @@ void CDROM::SetUseReadThread(bool enabled)
     m_reader.StopThread();
 }
 
+void CDROM::CPUClockChanged()
+{
+  // reschedule the disc read event
+  if (IsReadingOrPlaying())
+    m_drive_event->SetInterval(GetTicksForRead());
+}
+
 u8 CDROM::ReadRegister(u32 offset)
 {
   switch (offset)
@@ -612,23 +619,24 @@ TickCount CDROM::GetAckDelayForCommand(Command command)
 
 TickCount CDROM::GetTicksForRead()
 {
-  return m_mode.double_speed ? (MASTER_CLOCK / 150) : (MASTER_CLOCK / 75);
+  const TickCount tps = System::GetTicksPerSecond();
+  return m_mode.double_speed ? (tps / 150) : (tps / 75);
 }
 
 TickCount CDROM::GetTicksForSeek(CDImage::LBA new_lba)
 {
+  const TickCount tps = System::GetTicksPerSecond();
   const CDImage::LBA current_lba = m_secondary_status.motor_on ? m_current_lba : 0;
   const u32 lba_diff = static_cast<u32>((new_lba > current_lba) ? (new_lba - current_lba) : (current_lba - new_lba));
 
   // Formula from Mednafen.
   TickCount ticks = std::max<TickCount>(
     20000, static_cast<u32>(
-             ((static_cast<u64>(lba_diff) * static_cast<u64>(MASTER_CLOCK) * static_cast<u64>(1000)) / (72 * 60 * 75)) /
-             1000));
+             ((static_cast<u64>(lba_diff) * static_cast<u64>(tps) * static_cast<u64>(1000)) / (72 * 60 * 75)) / 1000));
   if (!m_secondary_status.motor_on)
-    ticks += MASTER_CLOCK;
+    ticks += tps;
   if (lba_diff >= 2550)
-    ticks += static_cast<TickCount>(u64(MASTER_CLOCK) * 300 / 1000);
+    ticks += static_cast<TickCount>((u64(tps) * 300) / 1000);
   else
   {
     // When paused, the CDC seems to keep reading the disc until it hits the position it's set to, then skip 10-15
@@ -644,7 +652,7 @@ TickCount CDROM::GetTicksForSeek(CDImage::LBA new_lba)
     m_current_double_speed = m_mode.double_speed;
 
     // Approximate time for the motor to change speed?
-    ticks += static_cast<u32>(static_cast<double>(MASTER_CLOCK) * 0.1);
+    ticks += static_cast<u32>(static_cast<double>(tps) * 0.1);
   }
 
   Log_DevPrintf("Seek time for %u LBAs: %d", lba_diff, ticks);
@@ -788,7 +796,7 @@ void CDROM::ExecuteCommand()
         SendACKAndStat();
 
         m_drive_state = DriveState::ReadingTOC;
-        m_drive_event->Schedule(MASTER_CLOCK / 2); // half a second
+        m_drive_event->Schedule(System::GetTicksPerSecond() / 2); // half a second
       }
 
       EndCommand();
@@ -874,7 +882,7 @@ void CDROM::ExecuteCommand()
 
         m_async_command_parameter = session;
         m_drive_state = DriveState::ChangingSession;
-        m_drive_event->Schedule(MASTER_CLOCK / 2); // half a second
+        m_drive_event->Schedule(System::GetTicksPerSecond() / 2); // half a second
       }
 
       EndCommand();
@@ -1011,7 +1019,7 @@ void CDROM::ExecuteCommand()
         SendACKAndStat();
 
         m_drive_state = DriveState::Resetting;
-        m_drive_event->Schedule(MASTER_CLOCK);
+        m_drive_event->Schedule(System::GetTicksPerSecond());
       }
 
       EndCommand();

src/core/cdrom.h

@@ -31,6 +31,8 @@ public:
   void InsertMedia(std::unique_ptr<CDImage> media);
   std::unique_ptr<CDImage> RemoveMedia(bool force = false);
 
+  void CPUClockChanged();
+
   // I/O
   u8 ReadRegister(u32 offset);
   void WriteRegister(u32 offset, u8 value);

src/core/cpu_core.cpp

@@ -67,7 +67,7 @@ void Shutdown()
 void Reset()
 {
   g_state.pending_ticks = 0;
-  g_state.downcount = MAX_SLICE_SIZE;
+  g_state.downcount = 0;
 
   g_state.regs = {};
 

src/core/cpu_core.h

@@ -51,7 +51,7 @@ struct State
 {
   // ticks the CPU has executed
   TickCount pending_ticks = 0;
-  TickCount downcount = MAX_SLICE_SIZE;
+  TickCount downcount = 0;
 
   Registers regs = {};
   Cop0Registers cop0_regs = {};

src/core/gpu.cpp

@@ -57,6 +57,11 @@ void GPU::UpdateSettings()
   UpdateCRTCDisplayParameters();
 }
 
+void GPU::CPUClockChanged()
+{
+  UpdateCRTCConfig();
+}
+
 void GPU::UpdateResolutionScale() {}
 
 std::tuple<u32, u32> GPU::GetEffectiveDisplayResolution()
@@ -427,8 +432,9 @@ float GPU::ComputeHorizontalFrequency() const
 {
   const CRTCState& cs = m_crtc_state;
   TickCount fractional_ticks = 0;
-  return static_cast<float>(static_cast<double>(SystemTicksToCRTCTicks(MASTER_CLOCK, &fractional_ticks)) /
-                            static_cast<double>(cs.horizontal_total));
+  return static_cast<float>(
+    static_cast<double>(SystemTicksToCRTCTicks(System::GetTicksPerSecond(), &fractional_ticks)) /
+    static_cast<double>(cs.horizontal_total));
 }
 
 float GPU::ComputeVerticalFrequency() const
@@ -436,8 +442,9 @@ float GPU::ComputeVerticalFrequency() const
   const CRTCState& cs = m_crtc_state;
   const TickCount ticks_per_frame = cs.horizontal_total * cs.vertical_total;
   TickCount fractional_ticks = 0;
-  return static_cast<float>(static_cast<double>(SystemTicksToCRTCTicks(MASTER_CLOCK, &fractional_ticks)) /
-                            static_cast<double>(ticks_per_frame));
+  return static_cast<float>(
+    static_cast<double>(SystemTicksToCRTCTicks(System::GetTicksPerSecond(), &fractional_ticks)) /
+    static_cast<double>(ticks_per_frame));
 }
 
 float GPU::GetDisplayAspectRatio() const
@@ -459,7 +466,7 @@ void GPU::UpdateCRTCConfig()
     cs.current_scanline %= PAL_TOTAL_LINES;
     cs.horizontal_total = PAL_TICKS_PER_LINE;
     cs.horizontal_sync_start = PAL_HSYNC_TICKS;
-    cs.current_tick_in_scanline %= PAL_TICKS_PER_LINE;
+    cs.current_tick_in_scanline %= System::ScaleTicksToOverclock(PAL_TICKS_PER_LINE);
   }
   else
   {
@@ -467,7 +474,7 @@ void GPU::UpdateCRTCConfig()
     cs.current_scanline %= NTSC_TOTAL_LINES;
     cs.horizontal_total = NTSC_TICKS_PER_LINE;
     cs.horizontal_sync_start = NTSC_HSYNC_TICKS;
-    cs.current_tick_in_scanline %= NTSC_TICKS_PER_LINE;
+    cs.current_tick_in_scanline %= System::ScaleTicksToOverclock(NTSC_TICKS_PER_LINE);
   }
 
   cs.in_hblank = (cs.current_tick_in_scanline >= cs.horizontal_sync_start);
@@ -498,6 +505,12 @@ void GPU::UpdateCRTCConfig()
     cs.current_tick_in_scanline %= NTSC_TICKS_PER_LINE;
   }
 
+  cs.horizontal_display_start =
+    static_cast<u16>(System::ScaleTicksToOverclock(static_cast<TickCount>(cs.horizontal_display_start)));
+  cs.horizontal_display_end =
+    static_cast<u16>(System::ScaleTicksToOverclock(static_cast<TickCount>(cs.horizontal_display_end)));
+  cs.horizontal_total = static_cast<u16>(System::ScaleTicksToOverclock(static_cast<TickCount>(cs.horizontal_total)));
+
   System::SetThrottleFrequency(ComputeVerticalFrequency());
 
   UpdateCRTCDisplayParameters();

src/core/gpu.h

@@ -132,6 +132,8 @@ public:
   // Render statistics debug window.
   void DrawDebugStateWindow();
 
+  void CPUClockChanged();
+
   // MMIO access
   u32 ReadRegister(u32 offset);
   void WriteRegister(u32 offset, u32 value);

src/core/host_interface.cpp

@@ -543,6 +543,14 @@ void HostInterface::CheckForSettingsChanges(const Settings& old_settings)
 {
   if (System::IsValid())
   {
+    if (g_settings.cpu_overclock_active != old_settings.cpu_overclock_active ||
+        (g_settings.cpu_overclock_active &&
+         (g_settings.cpu_overclock_numerator != old_settings.cpu_overclock_numerator ||
+          g_settings.cpu_overclock_denominator != old_settings.cpu_overclock_denominator)))
+    {
+      System::UpdateOverclock();
+    }
+
     if (g_settings.gpu_renderer != old_settings.gpu_renderer ||
         g_settings.gpu_use_debug_device != old_settings.gpu_use_debug_device)
     {

src/core/memory_card.cpp

@@ -13,9 +13,8 @@ MemoryCard::MemoryCard()
 {
   m_FLAG.no_write_yet = true;
 
-  m_save_event =
-    TimingEvents::CreateTimingEvent("Memory Card Host Flush", SAVE_DELAY_IN_SYSCLK_TICKS, SAVE_DELAY_IN_SYSCLK_TICKS,
-                                    std::bind(&MemoryCard::SaveIfChanged, this, true), false);
+  m_save_event = TimingEvents::CreateTimingEvent("Memory Card Host Flush", GetSaveDelayInTicks(), GetSaveDelayInTicks(),
+                                                 std::bind(&MemoryCard::SaveIfChanged, this, true), false);
 }
 
 MemoryCard::~MemoryCard()
@@ -23,6 +22,11 @@ MemoryCard::~MemoryCard()
   SaveIfChanged(false);
 }
 
+TickCount MemoryCard::GetSaveDelayInTicks()
+{
+  return System::GetTicksPerSecond() * SAVE_DELAY_IN_SECONDS;
+}
+
 void MemoryCard::Reset()
 {
   ResetTransferState();
@@ -309,5 +313,5 @@ void MemoryCard::QueueFileSave()
     return;
 
   // save in one second, that should be long enough for everything to finish writing
-  m_save_event->Schedule(SAVE_DELAY_IN_SYSCLK_TICKS);
+  m_save_event->Schedule(GetSaveDelayInTicks());
 }

src/core/memory_card.h

@@ -35,7 +35,6 @@ private:
   {
     // save in three seconds, that should be long enough for everything to finish writing
     SAVE_DELAY_IN_SECONDS = 5,
-    SAVE_DELAY_IN_SYSCLK_TICKS = MASTER_CLOCK * SAVE_DELAY_IN_SECONDS,
   };
 
   union FLAG
@@ -74,6 +73,8 @@ private:
     WriteEnd,
   };
 
+  static TickCount GetSaveDelayInTicks();
+
   bool LoadFromFile();
   bool SaveIfChanged(bool display_osd_message);
   void QueueFileSave();

src/core/save_state_version.h

@@ -2,7 +2,7 @@
 #include "types.h"
 
 static constexpr u32 SAVE_STATE_MAGIC = 0x43435544;
-static constexpr u32 SAVE_STATE_VERSION = 41;
+static constexpr u32 SAVE_STATE_VERSION = 42;
 
 #pragma pack(push, 4)
 struct SAVE_STATE_HEADER

src/core/settings.cpp

@@ -5,6 +5,7 @@
 #include "host_interface.h"
 #include <algorithm>
 #include <array>
+#include <numeric>
 
 Settings g_settings;
 
@@ -75,6 +76,28 @@ bool Settings::HasAnyPerGameMemoryCards() const
   });
 }
 
+void Settings::CPUOverclockPercentToFraction(u32 percent, u32* numerator, u32* denominator)
+{
+  const u32 percent_gcd = std::gcd(percent, 100);
+  *numerator = percent / percent_gcd;
+  *denominator = 100u / percent_gcd;
+}
+
+u32 Settings::CPUOverclockFractionToPercent(u32 numerator, u32 denominator)
+{
+  return (numerator * 100u) / denominator;
+}
+
+void Settings::SetCPUOverclockPercent(u32 percent)
+{
+  CPUOverclockPercentToFraction(percent, &cpu_overclock_numerator, &cpu_overclock_denominator);
+}
+
+u32 Settings::GetCPUOverclockPercent() const
+{
+  return CPUOverclockFractionToPercent(cpu_overclock_numerator, cpu_overclock_denominator);
+}
+
 void Settings::Load(SettingsInterface& si)
 {
   region =
@@ -95,6 +118,10 @@ void Settings::Load(SettingsInterface& si)
     ParseCPUExecutionMode(
       si.GetStringValue("CPU", "ExecutionMode", GetCPUExecutionModeName(DEFAULT_CPU_EXECUTION_MODE)).c_str())
       .value_or(DEFAULT_CPU_EXECUTION_MODE);
+  cpu_overclock_numerator = std::max(si.GetIntValue("CPU", "OverclockNumerator", 1), 1);
+  cpu_overclock_denominator = std::max(si.GetIntValue("CPU", "OverclockDenominator", 1), 1);
+  cpu_overclock_enable = si.GetBoolValue("CPU", "OverclockEnable", false);
+  cpu_overclock_active = (cpu_overclock_enable && (cpu_overclock_numerator != 1 || cpu_overclock_denominator != 1));
   cpu_recompiler_memory_exceptions = si.GetBoolValue("CPU", "RecompilerMemoryExceptions", false);
   cpu_recompiler_icache = si.GetBoolValue("CPU", "RecompilerICache", false);
 
@@ -218,6 +245,9 @@ void Settings::Save(SettingsInterface& si) const
   si.SetBoolValue("Main", "AutoLoadCheats", auto_load_cheats);
 
   si.SetStringValue("CPU", "ExecutionMode", GetCPUExecutionModeName(cpu_execution_mode));
+  si.SetBoolValue("CPU", "OverclockEnable", cpu_overclock_enable);
+  si.SetIntValue("CPU", "OverclockNumerator", cpu_overclock_numerator);
+  si.SetIntValue("CPU", "OverclockDenominator", cpu_overclock_denominator);
   si.SetBoolValue("CPU", "RecompilerMemoryExceptions", cpu_recompiler_memory_exceptions);
   si.SetBoolValue("CPU", "RecompilerICache", cpu_recompiler_icache);
 

src/core/settings.h

@@ -70,6 +70,10 @@ struct Settings
   ConsoleRegion region = ConsoleRegion::Auto;
 
   CPUExecutionMode cpu_execution_mode = CPUExecutionMode::Interpreter;
+  u32 cpu_overclock_numerator = 1;
+  u32 cpu_overclock_denominator = 1;
+  bool cpu_overclock_enable = false;
+  bool cpu_overclock_active = false;
   bool cpu_recompiler_memory_exceptions = false;
   bool cpu_recompiler_icache = false;
 
@@ -174,6 +178,12 @@ struct Settings
 
   bool HasAnyPerGameMemoryCards() const;
 
+  static void CPUOverclockPercentToFraction(u32 percent, u32* numerator, u32* denominator);
+  static u32 CPUOverclockFractionToPercent(u32 numerator, u32 denominator);
+
+  void SetCPUOverclockPercent(u32 percent);
+  u32 GetCPUOverclockPercent() const;
+
   enum : u32
   {
     DEFAULT_DMA_MAX_SLICE_TICKS = 1000,

src/core/spu.cpp

@@ -21,7 +21,10 @@ SPU::~SPU() = default;
 
 void SPU::Initialize()
 {
-  m_tick_event = TimingEvents::CreateTimingEvent("SPU Sample", SYSCLK_TICKS_PER_SPU_TICK, SYSCLK_TICKS_PER_SPU_TICK,
+  // (X * D) / N / 768 -> (X * D) / (N * 768)
+  m_cpu_ticks_per_spu_tick = System::ScaleTicksToOverclock(SYSCLK_TICKS_PER_SPU_TICK);
+  m_cpu_tick_divider = static_cast<TickCount>(g_settings.cpu_overclock_numerator * SYSCLK_TICKS_PER_SPU_TICK);
+  m_tick_event = TimingEvents::CreateTimingEvent("SPU Sample", m_cpu_ticks_per_spu_tick, m_cpu_ticks_per_spu_tick,
                                                  std::bind(&SPU::Execute, this, std::placeholders::_1), false);
   m_transfer_event =
     TimingEvents::CreateTimingEvent("SPU Transfer", TRANSFER_TICKS_PER_HALFWORD, TRANSFER_TICKS_PER_HALFWORD,
@@ -30,6 +33,15 @@ void SPU::Initialize()
   Reset();
 }
 
+void SPU::CPUClockChanged()
+{
+  // (X * D) / N / 768 -> (X * D) / (N * 768)
+  m_cpu_ticks_per_spu_tick = System::ScaleTicksToOverclock(SYSCLK_TICKS_PER_SPU_TICK);
+  m_cpu_tick_divider = static_cast<TickCount>(g_settings.cpu_overclock_numerator * SYSCLK_TICKS_PER_SPU_TICK);
+  m_ticks_carry = 0;
+  UpdateEventInterval();
+}
+
 void SPU::Shutdown()
 {
   m_tick_event.reset();
@@ -680,8 +692,19 @@ void SPU::IncrementCaptureBufferPosition()
 
 void SPU::Execute(TickCount ticks)
 {
-  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;
+  u32 remaining_frames;
+  if (g_settings.cpu_overclock_active)
+  {
+    // (X * D) / N / 768 -> (X * D) / (N * 768)
+    const u64 num = (static_cast<u64>(ticks) * g_settings.cpu_overclock_denominator) + static_cast<u32>(m_ticks_carry);
+    remaining_frames = static_cast<u32>(num / m_cpu_tick_divider);
+    m_ticks_carry = static_cast<TickCount>(num % m_cpu_tick_divider);
+  }
+  else
+  {
+    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;
+  }
 
   while (remaining_frames > 0)
   {
@@ -796,14 +819,19 @@ void SPU::UpdateEventInterval()
 
   // TODO: Make this predict how long until the interrupt will be hit instead...
   const u32 interval = (m_SPUCNT.enable && m_SPUCNT.irq9_enable) ? 1 : max_slice_frames;
-  const TickCount interval_ticks = static_cast<TickCount>(interval) * SYSCLK_TICKS_PER_SPU_TICK;
+  const TickCount interval_ticks = static_cast<TickCount>(interval) * m_cpu_ticks_per_spu_tick;
   if (m_tick_event->IsActive() && m_tick_event->GetInterval() == interval_ticks)
     return;
 
   // Ensure all pending ticks have been executed, since we won't get them back after rescheduling.
   m_tick_event->InvokeEarly(true);
   m_tick_event->SetInterval(interval_ticks);
-  m_tick_event->Schedule(interval_ticks - m_ticks_carry);
+
+  TickCount downcount = interval_ticks;
+  if (!g_settings.cpu_overclock_active)
+    downcount -= m_ticks_carry;
+
+  m_tick_event->Schedule(downcount);
 }
 
 void SPU::ExecuteTransfer(TickCount ticks)

src/core/spu.h

@@ -2,6 +2,7 @@
 #include "common/bitfield.h"
 #include "common/fifo_queue.h"
 #include "types.h"
+#include "system.h"
 #include <array>
 #include <memory>
 
@@ -20,6 +21,7 @@ public:
   ~SPU();
 
   void Initialize();
+  void CPUClockChanged();
   void Shutdown();
   void Reset();
   bool DoState(StateWrapper& sw);
@@ -54,7 +56,7 @@ private:
   static constexpr u32 VOICE_ADDRESS_SHIFT = 3;
   static constexpr u32 NUM_SAMPLES_PER_ADPCM_BLOCK = 28;
   static constexpr u32 SAMPLE_RATE = 44100;
-  static constexpr u32 SYSCLK_TICKS_PER_SPU_TICK = MASTER_CLOCK / SAMPLE_RATE; // 0x300
+  static constexpr u32 SYSCLK_TICKS_PER_SPU_TICK = System::MASTER_CLOCK / SAMPLE_RATE; // 0x300
   static constexpr s16 ENVELOPE_MIN_VOLUME = 0;
   static constexpr s16 ENVELOPE_MAX_VOLUME = 0x7FFF;
   static constexpr u32 CAPTURE_BUFFER_SIZE_PER_CHANNEL = 0x400;
@@ -370,6 +372,8 @@ private:
   std::unique_ptr<TimingEvent> m_transfer_event;
   std::unique_ptr<Common::WAVWriter> m_dump_writer;
   TickCount m_ticks_carry = 0;
+  TickCount m_cpu_ticks_per_spu_tick = 0;
+  TickCount m_cpu_tick_divider = 0;
 
   SPUCNT m_SPUCNT = {};
   SPUSTAT m_SPUSTAT = {};

src/core/system.cpp

@@ -68,6 +68,8 @@ static void UpdateRunningGame(const char* path, CDImage* image);
 static State s_state = State::Shutdown;
 
 static ConsoleRegion s_region = ConsoleRegion::NTSC_U;
+TickCount g_ticks_per_second = MASTER_CLOCK;
+static TickCount s_max_slice_ticks = MASTER_CLOCK / 10;
 static u32 s_frame_number = 1;
 static u32 s_internal_frame_number = 1;
 
@@ -143,6 +145,22 @@ bool IsPALRegion()
   return s_region == ConsoleRegion::PAL;
 }
 
+TickCount GetMaxSliceTicks()
+{
+  return s_max_slice_ticks;
+}
+
+void UpdateOverclock()
+{
+  g_ticks_per_second = ScaleTicksToOverclock(MASTER_CLOCK);
+  s_max_slice_ticks = ScaleTicksToOverclock(MASTER_CLOCK / 10);
+  g_spu.CPUClockChanged();
+  g_cdrom.CPUClockChanged();
+  g_gpu->CPUClockChanged();
+  g_timers.CPUClocksChanged();
+  UpdateThrottlePeriod();
+}
+
 u32 GetFrameNumber()
 {
   return s_frame_number;
@@ -682,6 +700,8 @@ bool Boot(const SystemBootParameters& params)
 
 bool Initialize(bool force_software_renderer)
 {
+  g_ticks_per_second = ScaleTicksToOverclock(MASTER_CLOCK);
+  s_max_slice_ticks = ScaleTicksToOverclock(MASTER_CLOCK / 10);
   s_frame_number = 1;
   s_internal_frame_number = 1;
 
@@ -725,6 +745,15 @@ bool Initialize(bool force_software_renderer)
   g_mdec.Initialize();
   g_sio.Initialize();
 
+  if (g_settings.cpu_overclock_active)
+  {
+    g_host_interface->AddFormattedOSDMessage(
+      10.0f,
+      g_host_interface->TranslateString("OSDMessage",
+                                        "CPU clock speed is set to %u%% (%u / %u). This may result in instability."),
+      g_settings.GetCPUOverclockPercent(), g_settings.cpu_overclock_numerator, g_settings.cpu_overclock_denominator);
+  }
+
   UpdateThrottlePeriod();
   return true;
 }
@@ -845,6 +874,31 @@ bool DoState(StateWrapper& sw)
   if (!sw.DoMarker("Events") || !TimingEvents::DoState(sw))
     return false;
 
+  if (!sw.DoMarker("Overclock"))
+    return false;
+
+  bool cpu_overclock_active = g_settings.cpu_overclock_active;
+  u32 cpu_overclock_numerator = g_settings.cpu_overclock_numerator;
+  u32 cpu_overclock_denominator = g_settings.cpu_overclock_denominator;
+  sw.Do(&cpu_overclock_active);
+  sw.Do(&cpu_overclock_numerator);
+  sw.Do(&cpu_overclock_denominator);
+
+  if (sw.IsReading() && (cpu_overclock_active != g_settings.cpu_overclock_active ||
+                         (cpu_overclock_active && (g_settings.cpu_overclock_numerator != cpu_overclock_numerator ||
+                                                   g_settings.cpu_overclock_denominator != cpu_overclock_denominator))))
+  {
+    g_host_interface->AddFormattedOSDMessage(
+      10.0f,
+      g_host_interface->TranslateString("OSDMessage",
+                                        "WARNING: CPU overclock (%u%%) was different in save state (%u%%)."),
+      g_settings.cpu_overclock_enable ? g_settings.GetCPUOverclockPercent() : 100u,
+      cpu_overclock_active ?
+        Settings::CPUOverclockFractionToPercent(cpu_overclock_numerator, cpu_overclock_denominator) :
+        100u);
+    UpdateOverclock();
+  }
+
   return !sw.HasError();
 }
 
@@ -1186,7 +1240,7 @@ void UpdatePerformanceCounters()
   s_fps = static_cast<float>(s_internal_frame_number - s_last_internal_frame_number) / time;
   s_last_internal_frame_number = s_internal_frame_number;
   s_speed = static_cast<float>(static_cast<double>(global_tick_counter - s_last_global_tick_counter) /
-                               (static_cast<double>(MASTER_CLOCK) * time)) *
+                               (static_cast<double>(g_ticks_per_second) * time)) *
             100.0f;
   s_last_global_tick_counter = global_tick_counter;
   s_fps_timer.Reset();

src/core/system.h

@@ -1,6 +1,7 @@
 #pragma once
 #include "common/timer.h"
 #include "host_interface.h"
+#include "settings.h"
 #include "timing_event.h"
 #include "types.h"
 #include <memory>
@@ -40,6 +41,11 @@ enum : u32
   MAX_SAVE_STATE_SIZE = 5 * 1024 * 1024
 };
 
+enum : TickCount
+{
+  MASTER_CLOCK = 44100 * 0x300 // 33868800Hz or 33.8688MHz, also used as CPU clock
+};
+
 enum class State
 {
   Shutdown,
@@ -48,6 +54,8 @@ enum class State
   Paused
 };
 
+extern TickCount g_ticks_per_second;
+
 /// Returns true if the filename is a PlayStation executable we can inject.
 bool IsExeFileName(const char* path);
 
@@ -80,6 +88,36 @@ bool IsValid();
 
 ConsoleRegion GetRegion();
 bool IsPALRegion();
+
+ALWAYS_INLINE TickCount GetTicksPerSecond()
+{
+  return g_ticks_per_second;
+}
+
+ALWAYS_INLINE_RELEASE TickCount ScaleTicksToOverclock(TickCount ticks)
+{
+  if (!g_settings.cpu_overclock_active)
+    return ticks;
+
+  return static_cast<TickCount>((static_cast<u64>(static_cast<u32>(ticks)) * g_settings.cpu_overclock_numerator) /
+                                g_settings.cpu_overclock_denominator);
+}
+
+ALWAYS_INLINE_RELEASE TickCount UnscaleTicksToOverclock(TickCount ticks, TickCount* remainder)
+{
+  if (!g_settings.cpu_overclock_active)
+    return ticks;
+
+  const u64 num =
+    (static_cast<u32>(ticks) * static_cast<u64>(g_settings.cpu_overclock_denominator)) + static_cast<u32>(*remainder);
+  const TickCount t = static_cast<u32>(num / g_settings.cpu_overclock_numerator);
+  *remainder = static_cast<u32>(num % g_settings.cpu_overclock_numerator);
+  return t;
+}
+
+TickCount GetMaxSliceTicks();
+void UpdateOverclock();
+
 u32 GetFrameNumber();
 u32 GetInternalFrameNumber();
 void FrameDone();

src/core/timers.cpp

@@ -41,6 +41,7 @@ void Timers::Reset()
     cs.irq_done = false;
   }
 
+  m_syclk_ticks_carry = 0;
   m_sysclk_div_8_carry = 0;
   UpdateSysClkEvent();
 }
@@ -59,6 +60,7 @@ bool Timers::DoState(StateWrapper& sw)
     sw.Do(&cs.irq_done);
   }
 
+  sw.Do(&m_syclk_ticks_carry);
   sw.Do(&m_sysclk_div_8_carry);
 
   if (sw.IsReading())
@@ -67,6 +69,11 @@ bool Timers::DoState(StateWrapper& sw)
   return !sw.HasError();
 }
 
+void Timers::CPUClocksChanged()
+{
+  m_syclk_ticks_carry = 0;
+}
+
 void Timers::SetGate(u32 timer, bool state)
 {
   CounterState& cs = m_states[timer];
@@ -157,6 +164,8 @@ void Timers::AddTicks(u32 timer, TickCount count)
 
 void Timers::AddSysClkTicks(TickCount sysclk_ticks)
 {
+  sysclk_ticks = System::UnscaleTicksToOverclock(sysclk_ticks, &m_syclk_ticks_carry);
+
   if (!m_states[0].external_counting_enabled && m_states[0].counting_enabled)
     AddTicks(0, sysclk_ticks);
   if (!m_states[1].external_counting_enabled && m_states[1].counting_enabled)
@@ -351,7 +360,9 @@ TickCount Timers::GetTicksUntilNextInterrupt() const
       min_ticks_for_this_timer = std::min(min_ticks_for_this_timer, static_cast<TickCount>(0xFFFF - cs.counter));
 
     if (cs.external_counting_enabled) // sysclk/8 for timer 2
-      min_ticks_for_this_timer = std::max<TickCount>(1, min_ticks_for_this_timer * 8);
+      min_ticks_for_this_timer = std::max<TickCount>(1, System::ScaleTicksToOverclock(min_ticks_for_this_timer * 8));
+    else
+      min_ticks_for_this_timer = std::max<TickCount>(1, System::ScaleTicksToOverclock(min_ticks_for_this_timer));
 
     min_ticks = std::min(min_ticks, min_ticks_for_this_timer);
   }
@@ -364,7 +375,7 @@ 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);
+    m_sysclk_event->Schedule(System::GetMaxSliceTicks());
   else
     m_sysclk_event->Schedule(ticks);
 }

src/core/timers.h

@@ -24,6 +24,8 @@ public:
 
   void DrawDebugStateWindow();
 
+  void CPUClocksChanged();
+
   // dot clock/hblank/sysclk div 8
   ALWAYS_INLINE bool IsUsingExternalClock(u32 timer) const { return m_states[timer].external_counting_enabled; }
 
@@ -92,7 +94,8 @@ private:
   std::unique_ptr<TimingEvent> m_sysclk_event;
 
   std::array<CounterState, NUM_TIMERS> m_states{};
-  u32 m_sysclk_div_8_carry = 0; // partial ticks for timer 3 with sysclk/8
+  TickCount m_syclk_ticks_carry = 0; // 0 unless overclocking is enabled
+  u32 m_sysclk_div_8_carry = 0;      // partial ticks for timer 3 with sysclk/8
 };
 
 extern Timers g_timers;

src/core/types.h

@@ -19,9 +19,6 @@ enum class MemoryAccessSize : u32
 
 using TickCount = s32;
 
-static constexpr TickCount MASTER_CLOCK = 44100 * 0x300; // 33868800Hz or 33.8688MHz, also used as CPU clock
-static constexpr TickCount MAX_SLICE_SIZE = MASTER_CLOCK / 10;
-
 enum class ConsoleRegion
 {
   Auto,