PPU: Add decrementer exception. Fix IIC behavior according to what li…

…nux expects.
xenon-emu · Jan 19, 2025 · 248db5e · 248db5e
1 parent 81a60aa
commit 248db5e
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Showing 3 changed files with 32 additions and 8 deletions.
diff --git a/Xenon/Core/XCPU/IIC/IIC.cpp b/Xenon/Core/XCPU/IIC/IIC.cpp
@@ -82,14 +82,22 @@ void Xe::XCPU::IIC::XenonIIC::readInterrupt(u64 intAddress, u64* intData)
 		*intData = _byteswap_uint64((u64)iicState.ppeIntCtrlBlck[ppeIntCtrlBlckID].REG_CPU_CURRENT_TSK_PRI);
 		break;
 	case Xe::XCPU::IIC::ACK:
-		// Check if the queue isn't empty (this probably isn't necessary)
+		// Check if the queue isn't empty (this probably isn't necessary).
 		if (iicState.ppeIntCtrlBlck[ppeIntCtrlBlckID].intQueue.empty() != true)
 		{
-			// Signal the Top Priority interrupt.
-			*intData = _byteswap_uint64(iicState.ppeIntCtrlBlck[ppeIntCtrlBlckID].intQueue.top());
-			// Set the ACK flag.
-			iicState.ppeIntCtrlBlck[ppeIntCtrlBlckID].intAck = true;
-			return;
+			// If the first interrupt is ACK'd we return PRIO_NONE.
+			if (iicState.ppeIntCtrlBlck[ppeIntCtrlBlckID].intAck)
+			{
+				*intData = _byteswap_uint64(PRIO_NONE);
+			}
+			else
+			{
+				// Signal the Top Priority interrupt.
+				*intData = _byteswap_uint64(iicState.ppeIntCtrlBlck[ppeIntCtrlBlckID].intQueue.top());
+				// Set the ACK flag.
+				iicState.ppeIntCtrlBlck[ppeIntCtrlBlckID].intAck = true;
+				return;
+			}
 		}
 		*intData = _byteswap_uint64(PRIO_NONE);
 		break;

diff --git a/Xenon/Core/XCPU/PPU/PPU.cpp b/Xenon/Core/XCPU/PPU/PPU.cpp
@@ -116,9 +116,17 @@ void PPU::StartExecution()
 						}
 					}
 
-					// Check if the IIC has an external interrupt pending if External interrupts are enabled.
+					// Check if External interrupts are enabled.
 					if (ppuState->ppuThread[ppuState->currentThread].SPR.MSR.EE)
 					{
+						// Check the decrementer.
+						// DEC[0] = 0 and a Decrementer exception does not exist.
+						if (ppuState->ppuThread[ppuState->currentThread].SPR.DEC == 0 &&
+							((ppuState->ppuThread[ppuState->currentThread].exceptReg & PPU_EX_DEC) == 0))
+						{
+							ppuState->ppuThread[ppuState->currentThread].exceptReg |= PPU_EX_DEC;
+						}
+						// Check if the IIC has an external interrupt pending.
 						if (xenonContext->xenonIIC.checkExtInterrupt(ppuState->ppuThread[ppuState->currentThread].SPR.PIR))
 						{
 							ppuState->ppuThread[ppuState->currentThread].exceptReg |= PPU_EX_EXT;
@@ -158,6 +166,13 @@ void PPU::StartExecution()
 					// Check if the IIC has an external interrupt pending if External interrupts are enabled.
 					if (ppuState->ppuThread[ppuState->currentThread].SPR.MSR.EE)
 					{
+						// Check the decrementer.
+						// DEC[0] = 0 and a Decrementer exception does not exist.
+						if (ppuState->ppuThread[ppuState->currentThread].SPR.DEC == 0 &&
+							((ppuState->ppuThread[ppuState->currentThread].exceptReg & PPU_EX_DEC) == 0))
+						{
+							ppuState->ppuThread[ppuState->currentThread].exceptReg |= PPU_EX_DEC;
+						}
 						if (xenonContext->xenonIIC.checkExtInterrupt(ppuState->ppuThread[ppuState->currentThread].SPR.PIR))
 						{
 							ppuState->ppuThread[ppuState->currentThread].exceptReg |= PPU_EX_EXT;

diff --git a/Xenon/Core/XCPU/PPU/PowerPC.h b/Xenon/Core/XCPU/PPU/PowerPC.h
@@ -204,7 +204,8 @@ struct PPU_THREAD_SPRS
 	// Data Address Register
 	u64 DAR;
 	// Decrementer Register
-	u32 DEC;
+	// The contents of the Decrementer are treated as a signed integer.
+	s32 DEC;
 	// Machine Status Save/Restore Register 0
 	u64 SRR0;
 	// Machine Status Save/Restore Register 1