From 787214ef44319d5845ab346fd7c193462d034890 Mon Sep 17 00:00:00 2001
From: slack <slack@ommadawn.(none)>
Date: Sun, 29 Jun 2008 03:30:27 +0200
Subject: [PATCH] More video code

---
 GBMemory.h |  1 +
 GBVideo.cc | 92 ++++++++++++++++++++++++++++++++++++++++++++++++------
 GBVideo.h  |  6 ++++
 Makefile   |  2 +-
 util.h     | 31 ++++++++++++++++++
 5 files changed, 122 insertions(+), 10 deletions(-)
 create mode 100644 util.h

diff --git a/GBMemory.h b/GBMemory.h
index 55563f1..56bd570 100644
--- a/GBMemory.h
+++ b/GBMemory.h
@@ -24,6 +24,7 @@ class GBIO
 	static const u16 OBP0 = 0xFF48; // Object Pallete 0 data(R/W)
 	static const u16 OBP1 = 0xFF49; // Object Pallete 1 data(R/W)
 	static const u16 DMA  = 0xFF46; // DMA Transfer & Start addr (W)
+	static const u16 IF   = 0xFF0F; // Interrupt flag       (R/W)
 
 	u8   read(int addr) const;
 	void write(int addr, u8 value);
diff --git a/GBVideo.cc b/GBVideo.cc
index 2789af8..86521de 100644
--- a/GBVideo.cc
+++ b/GBVideo.cc
@@ -1,5 +1,7 @@
 #include "GBVideo.h"
-	
+#include "gbcore.h"
+#include "util.h"
+
 GBVideo::GBVideo(GameBoy *core):
 	display(0),
 	core(core)
@@ -20,22 +22,38 @@ GBVideo::~GBVideo()
 
 u8   GBVideo::read_VRAM (int addr) const
 {
-	return VRAM[addr-VRAM_BASE];
+	int STAT = memory.read(GBIO::STAT);
+	if ((STAT & 3) == 3)
+		return 0xFF; // VRAM access disabled
+	else
+		return VRAM[addr-VRAM_BASE];
 }
 
 u8   GBVideo::read_OAM  (int addr) const
 {
-	return OAM[addr-OAM_BASE];
+	int STAT = memory.read(GBIO::STAT);
+	if ((STAT & 3) >= 2)
+		return 0xFF; // OAM access disabled
+	else
+		return OAM[addr-OAM_BASE];
 }
 
 void GBVideo::write_VRAM(int addr, u8 value)
 {
-	VRAM[addr-VRAM_BASE] = value;
+	int STAT = memory.read(GBIO::STAT);
+	if ((STAT & 3) == 3)
+		return; // VRAM access disabled
+	else
+		VRAM[addr-VRAM_BASE] = value;
 }
 
 void GBVideo::write_OAM (int addr, u8 value)
 {
-	OAM[addr-OAM_BASE] = value;
+	int STAT = memory.read(GBIO::STAT);
+	if ((STAT & 3) >= 2)
+		return; // OAM access disabled
+	else
+		OAM[addr-OAM_BASE] = value;
 }
 
 void GBVideo::update()
@@ -46,12 +64,68 @@ void GBVideo::update()
 	//70224 clks.)
 	//
 	// sequence:
-	// 2: 80 clocks           \
-	// 3: 172 clocks          |-> for each one of the 144 lines
-	// 0: 204 clocks (HBlank) /
+	// 2: 80 clocks  (reading OAM)       |
+	// 3: 172 clocks (reading OAM+VRAM)  |-> for each one of the 144 lines
+	// 0: 204 clocks (HBlank)            |
 	// 1: 4560 clocks -> VBlank
-	
+	//
+	// mode 2 starts at 0, 456, 912...
+	// mode 3 starts at 80, 536, 992...
+	// mode 0 starts at 252, 708, 1164...
+	// vblank starts at 65664
+
+	int STAT = core->memory.read(GBIO::STAT);
+	int LYC  = core->memory.read(GBIO::LYC);
+	int LY   = core->memory.read(GBIO::LY);
+
 	int t = core->cycle_count % 70224;
 	
+	if (t >= 65665)
+	{
+		if (t == 65665 && check_bit(STAT,4))
+			core->irq(GameBoy::IRQ_VBLANK);
+
+		// preserve bits 3-6, set mode to 1 (VBlank) and coincidence to 0
+		STAT = (STAT&0xF8) | 1;
+	}
+	else
+	{
+		LY = t/456;
+		int hline_t = t%456;
+		if (LY == LYC)
+		{
+			STAT = set_bit(STAT, 2); // set coincidence flag
+			if (hline_t == 0 && check_bit(STAT, 6))
+				core->irq(GameBoy::IRQ_LCD_STAT);
+		}
+
+		if (hline_t < 80)
+		{
+			if (hline_t == 0 && check_bit(STAT, 5))
+				core->irq(GameBoy::IRQ_LCD_STAT);
+
+			// preserve bits 2-6, set mode 2
+			STAT = (STAT&0xFC) | 2;
+		}
+		else if (hline_t < 252)
+		{
+			// preserve bits 2-6, set mode 3
+			STAT = (STAT&0xFC) | 3;
+		}
+		else
+		{
+			// HBlank (preserve bits 2-6, mode = 0)
+			STAT = (STAT&0xFC);
+			if (hline_t == 252 && check_bit(STAT, 3))
+				core->irq(GameBoy::IRQ_LCD_STAT);
+		}
+		
+	}
+	
+	core->memory.write(GBIO::LY, LY);
+	core->memory.write(GBIO::STAT, STAT);
+
+	// Draw the background
+	
 
 }
diff --git a/GBVideo.h b/GBVideo.h
index 8e35bed..63c8d75 100644
--- a/GBVideo.h
+++ b/GBVideo.h
@@ -1,6 +1,11 @@
+#ifndef GBVIDEO_H
+#define GBVIDEO_H
+
 #include "GBMemory.h"
 #include "SDL.h"
 
+class GameBoy;
+
 class GBVideo
 {
 	SDL_Surface *display;
@@ -35,4 +40,5 @@ class GBVideo
 
 };
 
+#endif
 
diff --git a/Makefile b/Makefile
index dabd46a..927c588 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ all: tests
 
 tests: tests/test_gbrom tests/test_core
 
-GBVideo.o: GBVideo.cc GBVideo.h Logger.h
+GBVideo.o: GBVideo.cc GBVideo.h Logger.h util.h
 	g++ $(CXXFLAGS) -c -o $@ $<
 
 GBMemory.o: GBMemory.cc GBMemory.h Logger.h
diff --git a/util.h b/util.h
new file mode 100644
index 0000000..65a551f
--- /dev/null
+++ b/util.h
@@ -0,0 +1,31 @@
+#ifndef UTIL_H
+#define UTIL_H
+
+#include "sized_types.h"
+
+uint32 set_bit(uint32 pos, uint32 val)
+{
+	uint32 mask = 1<<pos;
+	return val | mask;
+}
+
+uint32 reset_bit(uint32 pos, uint32 val)
+{
+	uint32 mask = ~(1<<pos);
+	return val & mask;
+}
+
+uint32 flip_bit(uint32 pos, uint32 val)
+{
+	uint32 mask = 1<<pos;
+	return val ^ mask;
+}
+
+bool check_bit(uint32 pos, uint32 val)
+{
+	uint32 mask = 1<<pos;
+	return ((val&mask) != 0);
+}
+
+#endif
+
-- 
2.34.1