I've fixed Super Monkey Ball in some cases when the game write the WriteReadDistance need to be safe like the SafeCPRead.

This fix is not related with the previous commits, but the previous commits help me to see that because in the new scenery SMB was hanging. May be in the past also doesn't boot some times because of that.

Please Test FZero boot also. Thanks.

Source/Core/VideoCommon/Src/CommandProcessor.cpp

@@ -171,11 +171,23 @@ void Read16(u16& _rReturnValue, const u32 _Address)
 	case FIFO_LO_WATERMARK_HI:	_rReturnValue = ReadHigh(fifo.CPLoWatermark); return;
 
 	case FIFO_RW_DISTANCE_LO:
+		if (IsOnThread())
+			if(fifo.CPWritePointer >= fifo.SafeCPReadPointer)
+				_rReturnValue = ReadLow (fifo.CPWritePointer - fifo.SafeCPReadPointer);
+			else
+				_rReturnValue = ReadLow (fifo.CPEnd - fifo.CPWritePointer + fifo.SafeCPReadPointer);
+		else
 		_rReturnValue = ReadLow (fifo.CPReadWriteDistance);
 		DEBUG_LOG(COMMANDPROCESSOR, "read FIFO_RW_DISTANCE_LO : %04x", _rReturnValue);
 		return;
 	case FIFO_RW_DISTANCE_HI:
-		_rReturnValue = ReadHigh(fifo.CPReadWriteDistance);
+		if (IsOnThread())
+			if(fifo.CPWritePointer >= fifo.SafeCPReadPointer)
+				_rReturnValue = ReadHigh (fifo.CPWritePointer - fifo.SafeCPReadPointer);
+			else
+				_rReturnValue = ReadHigh (fifo.CPEnd - fifo.CPWritePointer + fifo.SafeCPReadPointer);
+		else
+ 		_rReturnValue = ReadHigh(fifo.CPReadWriteDistance);
 		DEBUG_LOG(COMMANDPROCESSOR, "read FIFO_RW_DISTANCE_HI : %04x", _rReturnValue);
 		return;
 	case FIFO_WRITE_POINTER_LO:
@@ -356,6 +368,7 @@ void Write16(const u16 _Value, const u32 _Address)
 		break;
 	case FIFO_READ_POINTER_HI:
 		WriteHigh((u32 &)fifo.CPReadPointer, _Value);
+		fifo.SafeCPReadPointer = fifo.CPReadPointer;
 		DEBUG_LOG(COMMANDPROCESSOR,"\t write to FIFO_READ_POINTER_HI : %04x", _Value);
 		break;
 
@@ -596,7 +609,7 @@ void SetCpStatusRegister()
 	// Here always there is one fifo attached to the GPU
 		
 	m_CPStatusReg.Breakpoint = fifo.bFF_Breakpoint;
-	m_CPStatusReg.ReadIdle = (fifo.CPReadPointer == fifo.CPWritePointer) || (fifo.CPReadPointer == fifo.CPBreakpoint) ;
+	m_CPStatusReg.ReadIdle = !fifo.CPReadWriteDistance || (fifo.CPReadPointer == fifo.CPWritePointer) || (fifo.CPReadPointer == fifo.CPBreakpoint) ;
 	m_CPStatusReg.CommandIdle = !fifo.CPReadWriteDistance;
 	m_CPStatusReg.UnderflowLoWatermark = fifo.bFF_LoWatermark;
 	m_CPStatusReg.OverflowHiWatermark = fifo.bFF_HiWatermark;