From 01175cf9eb219a4eafec72236dafb9afa6e94126 Mon Sep 17 00:00:00 2001
From: Adrian Conlon <Adrian.conlon@gmail.com>
Date: Tue, 8 Jan 2019 23:55:27 +0000
Subject: [PATCH] Add support for emulated SYNC and RDY lines. Untested, but
 feel close.

Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
---
 M6502/inc/mos6502.h   | 10 +++++++---
 M6502/src/mos6502.cpp | 15 +++++----------
 2 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/M6502/inc/mos6502.h b/M6502/inc/mos6502.h
index 34f598d..a07524e 100644
--- a/M6502/inc/mos6502.h
+++ b/M6502/inc/mos6502.h
@@ -43,7 +43,9 @@ namespace EightBit {
 		const auto& P() const { return p; }
 
 		auto& NMI() { return m_nmiLine; }	// In
-		auto& SO() { return m_soLine;  }	// In
+		auto& SO() { return m_soLine; }		// In
+		auto& SYNC() { return m_syncLine; }	// Out
+		auto& RDY() { return m_rdyLine; }	// In
 
 	protected:
 		virtual void handleRESET() final;
@@ -185,8 +187,10 @@ namespace EightBit {
 		uint8_t s = 0;		// stack pointer
 		uint8_t p = 0;		// processor status
 
-		PinLevel m_nmiLine = PinLevel::Low;
-		PinLevel m_soLine = PinLevel::Low;
+		PinLevel m_nmiLine = PinLevel::Low;		// Active low
+		PinLevel m_soLine = PinLevel::Low;		// Active low
+		PinLevel m_syncLine = PinLevel::Low;	// Active high
+		PinLevel m_rdyLine = PinLevel::Low;		// Active high
 
 		register16_t m_intermediate;
 
diff --git a/M6502/src/mos6502.cpp b/M6502/src/mos6502.cpp
index 54adc3b..40e9a29 100644
--- a/M6502/src/mos6502.cpp
+++ b/M6502/src/mos6502.cpp
@@ -21,13 +21,12 @@ void EightBit::MOS6502::powerOn() {
 int EightBit::MOS6502::step() {
 	resetCycles();
 	ExecutingInstruction.fire(*this);
-	if (LIKELY(powered())) {
+	if (LIKELY(powered() && raised(RDY()))) {
 		if (UNLIKELY(lowered(SO())))
 			handleSO();
+		lower(SYNC());	// Instruction fetch beginning
 		opcode() = fetchByte();
-		if (UNLIKELY(lowered(HALT())))
-			handleHALT();
-		else if (UNLIKELY(lowered(RESET())))
+		if (UNLIKELY(lowered(RESET())))
 			handleRESET();
 		else if (UNLIKELY(lowered(NMI())))
 			handleNMI();
@@ -46,10 +45,6 @@ void EightBit::MOS6502::handleSO() {
 	P() |= VF;
 }
 
-void EightBit::MOS6502::handleHALT() {
-	opcode() = 0xea;	// NOP
-}
-
 void EightBit::MOS6502::handleRESET() {
 	raise(RESET());
 	m_handlingRESET = true;
@@ -58,14 +53,12 @@ void EightBit::MOS6502::handleRESET() {
 
 
 void EightBit::MOS6502::handleNMI() {
-	raise(HALT());
 	raise(NMI());
 	m_handlingNMI = true;
 	opcode() = 0x00;	// BRK
 }
 
 void EightBit::MOS6502::handleIRQ() {
-	raise(HALT());
 	raise(INT());
 	m_handlingIRQ = true;
 	opcode() = 0x00;	// BRK
@@ -107,6 +100,8 @@ uint8_t EightBit::MOS6502::busRead() {
 
 int EightBit::MOS6502::execute() { 
 
+	raise(SYNC());	// Instruction fetch has now completed
+
 	switch (opcode()) {
 
 	case 0x00:	fetchByte(); interrupt();									break;	// BRK (implied)