From e42484d35c1c1951f0c0f413ccf41580e7f2c35f Mon Sep 17 00:00:00 2001
From: "Adrian.Conlon" <adrian.conlon@gmail.com>
Date: Fri, 1 Sep 2017 13:17:20 +0100
Subject: [PATCH] Better DIV implementation.  Incremented as a word and exposed
 as the high part in the DIV register.

Signed-off-by: Adrian.Conlon <adrian.conlon@gmail.com>
---
 LR35902/inc/Bus.h   |  9 ++++-----
 LR35902/src/Bus.cpp | 16 +++++-----------
 2 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/LR35902/inc/Bus.h b/LR35902/inc/Bus.h
index 210640d..21806e2 100644
--- a/LR35902/inc/Bus.h
+++ b/LR35902/inc/Bus.h
@@ -163,9 +163,9 @@ namespace EightBit {
 			return (peekRegister(TAC) & Processor::Bit2) == 0;
 		}
 
-		void incrementDIV() {
-			auto current = peekRegister(DIV);
-			pokeRegister(DIV, ++current);
+		void incrementDIV(int cycles) {
+			m_divCounter.word += cycles;
+			pokeRegister(DIV, m_divCounter.high);
 		}
 
 		void incrementTIMA() {
@@ -218,13 +218,12 @@ namespace EightBit {
 		int m_romBank;
 		int m_ramBank;
 
-		int m_divCounter;
+		register16_t m_divCounter;
 		int m_timerCounter;
 		int m_timerRate;
 
 		void Bus_WrittenByte(const AddressEventArgs& e);
 
-		void checkDiv(int cycles);
 		void checkTimer(int cycles);
 
 		void validateCartridgeType();
diff --git a/LR35902/src/Bus.cpp b/LR35902/src/Bus.cpp
index 5767797..3741f6b 100644
--- a/LR35902/src/Bus.cpp
+++ b/LR35902/src/Bus.cpp
@@ -12,17 +12,19 @@ EightBit::Bus::Bus()
   m_ramBankSwitching(false),
   m_romBank(1),
   m_ramBank(0),
-  m_divCounter(256),
   m_timerCounter(0),
   m_timerRate(0) {
 	m_bootRom.resize(0x100);
 	m_gameRom.resize(0x10000);
 	WrittenByte.connect(std::bind(&Bus::Bus_WrittenByte, this, std::placeholders::_1));
+	m_divCounter.word = 0xabcc;
 }
 
 void EightBit::Bus::reset() {
 	pokeRegister(NR52, 0xf1);
 	pokeRegister(LCDC, DisplayBackground | BackgroundCharacterDataSelection | LcdEnable);
+	m_divCounter.word = 0xabcc;
+	m_timerCounter = 0;
 }
 
 void EightBit::Bus::clear() {
@@ -109,7 +111,7 @@ void EightBit::Bus::Bus_WrittenByte(const AddressEventArgs& e) {
 
 		case BASE + DIV:	// R/W
 			Memory::reference() = 0;
-			m_timerCounter = 0;
+			m_timerCounter = m_divCounter.word = 0;
 			break;
 		case BASE + TIMA:	// R/W
 		case BASE + TMA:	// R/W
@@ -164,18 +166,10 @@ void EightBit::Bus::Bus_WrittenByte(const AddressEventArgs& e) {
 }
 
 void EightBit::Bus::checkTimers(int cycles) {
-	checkDiv(cycles);
+	incrementDIV(cycles);
 	checkTimer(cycles);
 }
 
-void EightBit::Bus::checkDiv(int cycles) {
-	m_divCounter -= cycles;
-	if (m_divCounter <= 0) {
-		m_divCounter = 256;
-		incrementDIV();
-	}
-}
-
 void EightBit::Bus::checkTimer(int cycles) {
 	if (timerEnabled()) {
 		m_timerCounter -= cycles;