PCE: Tweak trigger for RCR counter increments

The RCR counter doesn't appear to increment unless the HDW mode (e.g the visible scanline) actually starts. On the other hand, the vertical mode counter will get clocked even if the VDC doesn't hit HDW (trigger seems to be earlier, currently set to be the same timing as the Y scroll latch). The RCR IRQ could occur later than on hardware because of this

Core/PCE/PceVdc.cpp

@@ -138,7 +138,7 @@ void PceVdc::ProcessEvent()
 
 	switch(_nextEvent) {
 		case PceVdcEvent::LatchScrollY:
-			_needRcrIncrement = true;
+			_needVCounterClock = true;
 			_latchClockY = _state.HClock;
 			IncScrollY();
 			if(!_state.BurstModeEnabled) {
@@ -157,7 +157,6 @@ void PceVdc::ProcessEvent()
 			break;
 
 		case PceVdcEvent::HdsIrqTrigger:
-			_needRcrIncrement = true;
 			if(_evalStartCycle >= 1365) {
 				//New row was about to start, but no time to start sprite eval, next row will have no sprites
 				_spriteCount = 0;
@@ -185,6 +184,7 @@ void PceVdc::SetHorizontalMode(PceVdcModeH hMode)
 			break;
 
 		case PceVdcModeH::Hdw:
+			_needVCounterClock = true;
 			_needRcrIncrement = true;
 			_nextEvent = PceVdcEvent::IncRcrCounter;
 			_nextEventCounter = DotsToClocks((_state.HvLatch.HorizDisplayWidth - 1) * 8) + 2;
@@ -664,16 +664,21 @@ void PceVdc::SetVertMode(PceVdcModeV vMode)
 	}
 }
 
-void PceVdc::IncrementRcrCounter()
+void PceVdc::ClockVCounter()
 {
-	_state.RcrCounter++;
-
-	_needRcrIncrement = false;
-
 	_vModeCounter--;
 	if(_vModeCounter == 0) {
 		SetVertMode((PceVdcModeV)(((int)_vMode + 1) % 4));
 	}
+	_needVCounterClock = false;
+}
+
+void PceVdc::IncrementRcrCounter()
+{
+	_state.RcrCounter++;
+
+	_needRcrIncrement = false;
+	ClockVCounter();
 
 	if(_vMode == PceVdcModeV::Vde && _state.RcrCounter == _state.HvLatch.VertDisplayWidth + 1) {
 		_needVertBlankIrq = true;
@@ -732,6 +737,8 @@ void PceVdc::ProcessEndOfScanline()
 
 	if(_needRcrIncrement) {
 		IncrementRcrCounter();
+	} else if(_needVCounterClock) {
+		ClockVCounter();
 	}
 
 	if(_hMode == PceVdcModeH::Hdw) {
@@ -1385,6 +1392,7 @@ void PceVdc::Serialize(Serializer& s)
 
 		SV(_screenOffsetX);
 		SV(_needRcrIncrement);
+		SV(_needVCounterClock);
 		SV(_needVertBlankIrq);
 		SV(_verticalBlankDone);
 

Core/PCE/PceVdc.h

@@ -80,6 +80,7 @@ class PceVdc final : public ISerializable
 
 	uint16_t _screenOffsetX = 0;
 	bool _needRcrIncrement = false;
+	bool _needVCounterClock = false;
 	bool _needVertBlankIrq = false;
 	bool _verticalBlankDone = false;
 
@@ -156,6 +157,7 @@ class PceVdc final : public ISerializable
 	__noinline void ProcessVramDmaTransfer();
 	__noinline void SetVertMode(PceVdcModeV vMode);
 	__noinline void SetHorizontalMode(PceVdcModeH hMode);
+	void ClockVCounter();
 
 	__noinline void ProcessVdcEvents();
 	__noinline void ProcessEvent();