From bc90c489c1a040117e22021b1c4a2210aa0af0ec Mon Sep 17 00:00:00 2001
From: Sour <mesenemu@gmail.com>
Date: Sat, 23 May 2020 12:38:31 -0400
Subject: [PATCH] GB: Improved EI and IRQ behavior Passes ei_sequence,
 ei_timing, ie_push, rapid_di_ei, reti_intr_timing

---
 Core/GbCpu.cpp | 25 ++++++++++++++++++++++---
 Core/GbTypes.h |  1 +
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/Core/GbCpu.cpp b/Core/GbCpu.cpp
index 76ac7de..8b1f886 100644
--- a/Core/GbCpu.cpp
+++ b/Core/GbCpu.cpp
@@ -49,18 +49,32 @@ void GbCpu::Exec()
 	if(irqVector) {
 		if(_state.IME) {
 			uint16_t oldPc = _state.PC;
-			_memoryManager->ClearIrqRequest(irqVector);
 			IncCycleCount();
 			IncCycleCount();
-			PushWord(_state.PC);
+
+			PushByte(_state.PC >> 8);
+			irqVector = _memoryManager->ProcessIrqRequests(); //Check IRQ line again before jumping (ie_push)
+			PushByte((uint8_t)_state.PC);
+
 			IncCycleCount();
+			
 			switch(irqVector) {
+				case 0:
+					//IRQ request bit is no longer set, jump to $0000 (ie_push test)
+					_state.PC = 0;
+					break;
+
 				case GbIrqSource::VerticalBlank: _state.PC = 0x40; break;
 				case GbIrqSource::LcdStat: _state.PC = 0x48; break;
 				case GbIrqSource::Timer: _state.PC = 0x50; break;
 				case GbIrqSource::Serial: _state.PC = 0x58; break;
 				case GbIrqSource::Joypad: _state.PC = 0x60; break;
 			}
+			if(irqVector) {
+				//Only clear IRQ bit if an IRQ was processed
+				_memoryManager->ClearIrqRequest(irqVector);
+			}
+
 			_state.IME = false;
 			_console->ProcessInterrupt<CpuType::Gameboy>(oldPc, _state.PC, false);
 		}
@@ -72,6 +86,11 @@ void GbCpu::Exec()
 		return;
 	}
 
+	if(_state.EiPending) {
+		_state.EiPending = false;
+		_state.IME = true;
+	}
+
 	ExecOpCode(ReadOpCode());
 }
 
@@ -1083,7 +1102,7 @@ void GbCpu::CCF()
 
 void GbCpu::EI()
 {
-	_state.IME = true;
+	_state.EiPending = true;
 }
 
 void GbCpu::DI()
diff --git a/Core/GbTypes.h b/Core/GbTypes.h
index 21da166..8b18fce 100644
--- a/Core/GbTypes.h
+++ b/Core/GbTypes.h
@@ -19,6 +19,7 @@ struct GbCpuState
 	uint8_t H;
 	uint8_t L;
 
+	bool EiPending;
 	bool IME;
 	bool Halted;
 };