From 5279ebb688d9a13519c8a0977c45a6e16e910e10 Mon Sep 17 00:00:00 2001
From: Sour <mesenemu@gmail.com>
Date: Sat, 23 May 2020 11:19:22 -0400
Subject: [PATCH] GB: Fixed OAM write behavior during DMA

---
 Core/GbDmaController.cpp | 2 +-
 Core/GbMemoryManager.cpp | 8 +++++++-
 Core/GbMemoryManager.h   | 1 +
 Core/GbPpu.cpp           | 5 +++--
 Core/GbPpu.h             | 2 +-
 5 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/Core/GbDmaController.cpp b/Core/GbDmaController.cpp
index cf2433a..c40f8af 100644
--- a/Core/GbDmaController.cpp
+++ b/Core/GbDmaController.cpp
@@ -14,7 +14,7 @@ void GbDmaController::Exec()
 {
 	if(_state.DmaCounter > 0) {
 		if(_state.DmaCounter <= 160) {
-			_memoryManager->Write(0xFE00 + (160 - _state.DmaCounter), _state.DmaReadBuffer);
+			_memoryManager->WriteDma(0xFE00 + (160 - _state.DmaCounter), _state.DmaReadBuffer);
 		}
 
 		_state.DmaCounter--;
diff --git a/Core/GbMemoryManager.cpp b/Core/GbMemoryManager.cpp
index 59a1aa0..87b22a9 100644
--- a/Core/GbMemoryManager.cpp
+++ b/Core/GbMemoryManager.cpp
@@ -151,6 +151,12 @@ bool GbMemoryManager::IsOamDmaRunning()
 	return _dmaController->IsOamDmaRunning();
 }
 
+void GbMemoryManager::WriteDma(uint16_t addr, uint8_t value)
+{
+	_console->ProcessMemoryRead<CpuType::Gameboy>(addr, value, MemoryOperationType::DmaWrite);
+	_ppu->WriteOam(addr, value, true);
+}
+
 uint8_t GbMemoryManager::ReadDma(uint16_t addr)
 {
 	uint8_t value = 0;
@@ -323,7 +329,7 @@ void GbMemoryManager::WriteRegister(uint16_t addr, uint8_t value)
 			}
 		}
 	} else if(addr >= 0xFE00) {
-		_ppu->WriteOam((uint8_t)addr, value);
+		_ppu->WriteOam((uint8_t)addr, value, false);
 	} else if(addr >= 0x8000 && addr <= 0x9FFF) {
 		_ppu->WriteVram(addr, value);
 	} else {
diff --git a/Core/GbMemoryManager.h b/Core/GbMemoryManager.h
index 11f32e7..ec0d9eb 100644
--- a/Core/GbMemoryManager.h
+++ b/Core/GbMemoryManager.h
@@ -57,6 +57,7 @@ public:
 
 	uint8_t Read(uint16_t addr, MemoryOperationType opType);
 	bool IsOamDmaRunning();
+	void WriteDma(uint16_t addr, uint8_t value);
 	uint8_t ReadDma(uint16_t addr);
 	void Write(uint16_t addr, uint8_t value);
 
diff --git a/Core/GbPpu.cpp b/Core/GbPpu.cpp
index fa4bb2f..6ad1ad2 100644
--- a/Core/GbPpu.cpp
+++ b/Core/GbPpu.cpp
@@ -521,9 +521,10 @@ uint8_t GbPpu::ReadOam(uint8_t addr)
 	return 0;
 }
 
-void GbPpu::WriteOam(uint8_t addr, uint8_t value)
+void GbPpu::WriteOam(uint8_t addr, uint8_t value, bool forDma)
 {
-	if(addr < 0xA0 && (int)_state.Mode <= (int)PpuMode::VBlank) {
+	//During DMA or rendering/oam evaluation, ignore writes to OAM
+	if(addr < 0xA0 && (int)_state.Mode <= (int)PpuMode::VBlank && (forDma || !_memoryManager->IsOamDmaRunning())) {
 		_oam[addr] = value;
 	}
 }
diff --git a/Core/GbPpu.h b/Core/GbPpu.h
index 1cc2f60..67adef8 100644
--- a/Core/GbPpu.h
+++ b/Core/GbPpu.h
@@ -84,7 +84,7 @@ public:
 	void WriteVram(uint16_t addr, uint8_t value);
 
 	uint8_t ReadOam(uint8_t addr);
-	void WriteOam(uint8_t addr, uint8_t value);
+	void WriteOam(uint8_t addr, uint8_t value, bool forDma);
 
 	uint8_t ReadCgbRegister(uint16_t addr);
 	void WriteCgbRegister(uint16_t addr, uint8_t value);