From 73a34f4faea2971dbe6ed14779f537b7eb4a69de Mon Sep 17 00:00:00 2001
From: "Adrian.Conlon" <adrian.conlon@gmail.com>
Date: Sat, 26 Aug 2017 09:46:53 +0100
Subject: [PATCH] Start a more careful documentation of the I/O registers.

Signed-off-by: Adrian.Conlon <adrian.conlon@gmail.com>
---
 LR35902/inc/Bus.h       | 48 ++++++++++++++++++++++++-------
 LR35902/src/Bus.cpp     | 63 +++++++++++++++++++++++++++++++++++------
 LR35902/src/LR35902.cpp |  6 ++--
 3 files changed, 95 insertions(+), 22 deletions(-)

diff --git a/LR35902/inc/Bus.h b/LR35902/inc/Bus.h
index ed1a154..210640d 100644
--- a/LR35902/inc/Bus.h
+++ b/LR35902/inc/Bus.h
@@ -89,6 +89,24 @@ namespace EightBit {
 			Keypad = Processor::Bit3					// Hi-Lo of P10-P13
 		};
 
+		enum LcdcControl {
+			DisplayBackground = Processor::Bit0,
+			ObjectEnable = Processor::Bit1,
+			ObjectBlockCompositionSelection = Processor::Bit2,
+			BackgroundCodeAreaSelection = Processor::Bit3,
+			BackgroundCharacterDataSelection = Processor::Bit4,
+			WindowEnable = Processor::Bit5,
+			WindowCodeAreaSelection = Processor::Bit6,
+			LcdEnable = Processor::Bit7
+		};
+
+		enum LcdStatusMode {
+			CpuAccessAllowed = 0b00,
+			VerticalBlankingPeriod = 0b01,
+			SearchingOamRam = 0b10,
+			TransferringDataToLcd = 0b11
+		};
+
 		Bus();
 
 		void reset();
@@ -96,17 +114,25 @@ namespace EightBit {
 		virtual void clear() override;
 
 		void triggerInterrupt(int cause) {
-			writeRegister(IF, readRegister(IF) | cause);
+			pokeRegister(IF, peekRegister(IF) | cause);
 		}
 
 		void writeRegister(int offset, uint8_t content) {
-			return Memory::write(BASE + offset, content);
+			Memory::write(BASE + offset, content);
+		}
+
+		void pokeRegister(int offset, uint8_t content) {
+			poke(BASE + offset, content);
 		}
 
 		uint8_t readRegister(int offset) {
 			return Memory::read(BASE + offset);
 		}
 
+		uint8_t peekRegister(int offset) {
+			return peek(BASE + offset);
+		}
+
 		void checkTimers(int cycles);
 
 		int timerClockTicks() {
@@ -126,7 +152,7 @@ namespace EightBit {
 		}
 
 		int timerClock() {
-			return readRegister(TAC) & Processor::Mask2;
+			return peekRegister(TAC) & Processor::Mask2;
 		}
 
 		bool timerEnabled() {
@@ -134,29 +160,29 @@ namespace EightBit {
 		}
 
 		bool timerDisabled() {
-			return (readRegister(TAC) & Processor::Bit2) == 0;
+			return (peekRegister(TAC) & Processor::Bit2) == 0;
 		}
 
 		void incrementDIV() {
-			auto current = readRegister(DIV);
-			writeRegister(DIV, ++current);
+			auto current = peekRegister(DIV);
+			pokeRegister(DIV, ++current);
 		}
 
 		void incrementTIMA() {
-			uint16_t updated = readRegister(TIMA) + 1;
+			uint16_t updated = peekRegister(TIMA) + 1;
 			if (updated & Processor::Bit8) {
 				triggerInterrupt(TimerOverflow);
-				updated = readRegister(TMA);
+				updated = peekRegister(TMA);
 			}
-			writeRegister(TIMA, updated & Processor::Mask8);
+			pokeRegister(TIMA, updated & Processor::Mask8);
 		}
 
 		void incrementLY() {
-			writeRegister(LY, (readRegister(LY) + 1) % TotalLineCount);
+			pokeRegister(LY, (peekRegister(LY) + 1) % TotalLineCount);
 		}
 
 		void resetLY() {
-			writeRegister(LY, 0);
+			pokeRegister(LY, 0);
 		}
 
 		void disableBootRom() { m_disableBootRom = true; }
diff --git a/LR35902/src/Bus.cpp b/LR35902/src/Bus.cpp
index beb722f..ab473ea 100644
--- a/LR35902/src/Bus.cpp
+++ b/LR35902/src/Bus.cpp
@@ -21,8 +21,8 @@ EightBit::Bus::Bus()
 }
 
 void EightBit::Bus::reset() {
-	writeRegister(NR52, 0xf1);
-	writeRegister(LCDC, 0x91);
+	pokeRegister(NR52, 0xf1);
+	pokeRegister(LCDC, DisplayBackground | BackgroundCharacterDataSelection | LcdEnable);
 }
 
 void EightBit::Bus::clear() {
@@ -102,16 +102,63 @@ void EightBit::Bus::Bus_WrittenByte(const AddressEventArgs& e) {
 
 	if (!handled) {
 		switch (address) {
-		case BASE + TAC:
-			m_timerRate = timerClockTicks();
+
+		case BASE + SB:		// R/W
+		case BASE + SC:		// R/W
 			break;
-		case BASE + BOOT_DISABLE:
-			m_disableBootRom = value != 0;
-			break;
-		case BASE + DIV:
+
+		case BASE + DIV:	// R/W
 			Memory::reference() = 0;
 			m_timerCounter = 0;
 			break;
+		case BASE + TIMA:	// R/W
+		case BASE + TMA:	// R/W
+			break;
+		case BASE + TAC:	// R/W
+			m_timerRate = timerClockTicks();
+			break;
+
+		case BASE + IF:		// R/W
+			break;
+
+		case BASE + NR10:
+		case BASE + NR11:
+		case BASE + NR12:
+		case BASE + NR13:
+		case BASE + NR14:
+		case BASE + NR22:
+		case BASE + NR24:
+		case BASE + NR30:
+		case BASE + NR42:
+		case BASE + NR44:
+		case BASE + NR50:
+		case BASE + NR51:
+		case BASE + NR52:
+			break;
+
+		case BASE + LCDC:
+		case BASE + STAT:
+		case BASE + SCY:
+		case BASE + SCX:
+		case BASE + DMA:
+			break;
+		case BASE + LY:		// R/O
+			Memory::reference() = 0;
+			break;
+		case BASE + BGP:
+		case BASE + OBP0:
+		case BASE + OBP1:
+		case BASE + WY:
+		case BASE + WX:
+			break;
+
+		case BASE + BOOT_DISABLE:
+			m_disableBootRom = value != 0;
+			break;
+
+		default:
+			if ((address > BASE) && (address < (BASE + 0x4c)))
+				assert(false);
 		}
 	}
 }
diff --git a/LR35902/src/LR35902.cpp b/LR35902/src/LR35902.cpp
index 944cbfe..9c0e1a8 100644
--- a/LR35902/src/LR35902.cpp
+++ b/LR35902/src/LR35902.cpp
@@ -332,14 +332,14 @@ void EightBit::LR35902::ccf(uint8_t& a, uint8_t& f) {
 int EightBit::LR35902::run(int limit) {
 	int current = 0;
 	do {
-		auto interruptEnable = m_bus.readRegister(Bus::IE);
-		auto interruptFlags = m_bus.readRegister(Bus::IF);
+		auto interruptEnable = m_bus.peekRegister(Bus::IE);
+		auto interruptFlags = m_bus.peekRegister(Bus::IF);
 		auto ime = IME();
 
 		auto masked = interruptEnable & interruptFlags;
 		if (masked) {
 			if (ime) {
-				m_bus.writeRegister(Bus::IF, 0);
+				m_bus.pokeRegister(Bus::IF, 0);
 			} else {
 				if (isHalted())
 					proceed();