Simplify timer code to scale them without state

src/common/Timer.cpp

@@ -76,8 +76,8 @@ void SleepPrecise(std::chrono::steady_clock::time_point targetTime)
 
 // Vector storing all the timers created
 static std::vector<TimerObject*> TimerList;
-// The frequency of the high resolution clock of the host
-uint64_t HostClockFrequency;
+// The frequency of the high resolution clock of the host, and the start time
+int64_t HostQPCFrequency, HostQPCStartTime;
 // Lock to acquire when accessing TimerList
 std::mutex TimerMtx;
 
@@ -86,9 +86,7 @@ std::mutex TimerMtx;
 uint64_t GetTime_NS(TimerObject* Timer)
 {
 #ifdef _WIN32
-	LARGE_INTEGER li;
-	QueryPerformanceCounter(&li);
-	uint64_t Ret = Muldiv64(li.QuadPart, SCALE_S_IN_NS, (uint32_t)HostClockFrequency);
+	uint64_t Ret = Timer_GetScaledPerformanceCounter(SCALE_S_IN_NS);
 #elif __linux__
 	static struct timespec ts;
 	clock_gettime(CLOCK_MONOTONIC_RAW, &ts);
@@ -194,9 +192,8 @@ void Timer_Start(TimerObject* Timer, uint64_t Expire_MS)
 void Timer_Init()
 {
 #ifdef _WIN32
-	LARGE_INTEGER freq;
-	QueryPerformanceFrequency(&freq);
-	HostClockFrequency = freq.QuadPart;
+	QueryPerformanceFrequency(reinterpret_cast<LARGE_INTEGER*>(&HostQPCFrequency));
+	QueryPerformanceCounter(reinterpret_cast<LARGE_INTEGER*>(&HostQPCStartTime));
 #elif __linux__
 	ClockFrequency = 0;
 #else
@@ -204,36 +201,17 @@ void Timer_Init()
 #endif
 }
 
-// ******************************************************************
-
-void ScaledPerformanceCounter::Reset(uint32_t frequency)
+int64_t Timer_GetScaledPerformanceCounter(int64_t Period)
 {
-	std::lock_guard<std::mutex> lock(m_mutex);
+	LARGE_INTEGER currentQPC;
+	QueryPerformanceCounter(&currentQPC);
 
-	m_frequencyFactor = Muldiv64(HostClockFrequency, SCALE_S_IN_NS, frequency);
+	// Scale frequency with overflow avoidance, like in std::chrono
+	// https://github.com/microsoft/STL/blob/6d2f8b0ed88ea6cba26cc2151f47f678442c1663/stl/inc/chrono#L703
+	const int64_t currentTime = currentQPC.QuadPart - HostQPCStartTime;
+	const int64_t whole = (currentTime / HostQPCFrequency) * Period;
+	const int64_t part  = (currentTime % HostQPCFrequency) * Period / HostQPCFrequency;
 
-	LARGE_INTEGER tsc;
-	QueryPerformanceCounter(&tsc);
-	m_lastQPC = tsc.QuadPart;
-
-	m_currentCount = 0;
-	m_currentRemainder = 0;
+	return whole + part;
 }
 
-uint64_t ScaledPerformanceCounter::Tick()
-{
-	std::lock_guard<std::mutex> lock(m_mutex);
-
-	LARGE_INTEGER qpc;
-	QueryPerformanceCounter(&qpc);
-
-	int64_t lastQpc = std::exchange(m_lastQPC, qpc.QuadPart);
-	qpc.QuadPart -= lastQpc;
-	qpc.QuadPart *= SCALE_S_IN_NS;
-	qpc.QuadPart += m_currentRemainder;
-	uint64_t quotient = qpc.QuadPart / m_frequencyFactor;
-	uint64_t remainder =  qpc.QuadPart % m_frequencyFactor;
-
-	m_currentRemainder = remainder;
-	return m_currentCount += quotient;
-}

src/common/Timer.h

@@ -54,7 +54,7 @@ typedef struct _TimerObject
 }
 TimerObject;
 
-extern uint64_t HostClockFrequency;
+extern int64_t HostQPCFrequency;
 
 /* Timer exported functions */
 TimerObject* Timer_Create(TimerCB Callback, void* Arg, std::string Name, bool IsXboxTimer);
@@ -64,25 +64,8 @@ void Timer_ChangeExpireTime(TimerObject* Timer, uint64_t Expire_ms);
 uint64_t GetTime_NS(TimerObject* Timer);
 void Timer_Init();
 
+int64_t Timer_GetScaledPerformanceCounter(int64_t Period);
+
 void SleepPrecise(std::chrono::steady_clock::time_point targetTime);
 
-// A stateful replacement for QueryPerformanceCounter, ticking at an arbitrary frequency
-// Thread-safe and designed to avoid overflows at all cost
-class ScaledPerformanceCounter
-{
-public:
-	ScaledPerformanceCounter() = default;
-	void Reset(uint32_t frequency);
-	uint64_t Tick();
-
-private:
-	std::mutex m_mutex;
-
-	uint64_t m_frequencyFactor;
-	int64_t m_lastQPC;
-
-	uint64_t m_currentCount;
-	uint64_t m_currentRemainder;
-};
-
 #endif

src/core/hle/DSOUND/DirectSound/DirectSound.cpp

@@ -53,16 +53,10 @@
 // TODO: Move these to LLE APUDevice once we have one!
 
 static constexpr uint32_t APU_TIMER_FREQUENCY = 48000;
-static ScaledPerformanceCounter ApuCounter;
-
-void ResetApuTimer()
-{
-    ApuCounter.Reset(APU_TIMER_FREQUENCY);
-}
 
 uint32_t GetAPUTime()
 {
-    return static_cast<uint32_t>(ApuCounter.Tick());
+    return static_cast<int32_t>(Timer_GetScaledPerformanceCounter(APU_TIMER_FREQUENCY));
 }
 
 
@@ -135,8 +129,6 @@ xbox::hresult_xt WINAPI xbox::EMUPATCH(DirectSoundCreate)
         dsound_thread = std::thread(dsound_thread_worker, nullptr);
     }
 
-	ResetApuTimer();
-
     // Set this flag when this function is called
     g_bDSoundCreateCalled = TRUE;
 

src/core/kernel/exports/EmuKrnlKe.cpp

@@ -327,26 +327,15 @@ void InitDpcThread()
 
 static constexpr uint32_t XBOX_TSC_FREQUENCY = 733333333; // Xbox Time Stamp Counter Frequency = 733333333 (CPU Clock)
 static constexpr uint32_t XBOX_ACPI_FREQUENCY = 3375000;  // Xbox ACPI frequency (3.375 mhz)
-static ScaledPerformanceCounter TscCounter, AcpiCounter;
 
 ULONGLONG CxbxGetPerformanceCounter(bool acpi)
 {
-	if (acpi == false) {
-		return TscCounter.Tick();
-	} else if (acpi == true) {
-		return AcpiCounter.Tick();
-	}
-
-	LARGE_INTEGER tsc;
-	QueryPerformanceCounter(&tsc);
-	return static_cast<ULONGLONG>(tsc.QuadPart);
+	const int64_t period = acpi ? XBOX_ACPI_FREQUENCY : XBOX_TSC_FREQUENCY;
+	return Timer_GetScaledPerformanceCounter(period);
 }
 
 void CxbxInitPerformanceCounters()
 {
-	TscCounter.Reset(XBOX_TSC_FREQUENCY);
-	AcpiCounter.Reset(XBOX_ACPI_FREQUENCY);
-
 	// Let's initialize the Dpc handling thread too,
 	// here for now (should be called by our caller)
 	InitDpcThread();

src/core/kernel/init/CxbxKrnl.cpp

@@ -391,8 +391,8 @@ static void CxbxKrnlClockThread(void* pVoid)
 	LastTicks = CurrentTicks.QuadPart;
 
 	Error += (Delta * SCALE_S_IN_US);
-	Microseconds = Error / HostClockFrequency;
-	Error -= (Microseconds * HostClockFrequency);
+	Microseconds = Error / HostQPCFrequency;
+	Error -= (Microseconds * HostQPCFrequency);
 
 	UnaccountedMicroseconds += Microseconds;
 	IncrementScaling = (unsigned int)(UnaccountedMicroseconds / 1000); // -> 1 ms = 1000us -> time between two xbox clock interrupts