From 25321e78e7667f62dd05f938a86efec5c6ee6b58 Mon Sep 17 00:00:00 2001
From: Adrian Conlon <Adrian.conlon@gmail.com>
Date: Tue, 8 Jan 2019 01:32:43 +0000
Subject: [PATCH] Now that HALT/RESET/NMI/IRQ and BRK have a unified
 architecture, I think this wraps up the instruction handler of the 6502.

Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
---
 M6502/inc/mos6502.h   |  4 ++++
 M6502/src/mos6502.cpp | 36 ++++++++++++++++++++++--------------
 2 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/M6502/inc/mos6502.h b/M6502/inc/mos6502.h
index b4a1aa7..97d82a1 100644
--- a/M6502/inc/mos6502.h
+++ b/M6502/inc/mos6502.h
@@ -186,5 +186,9 @@ namespace EightBit {
 		PinLevel m_soLine = PinLevel::Low;
 
 		register16_t m_intermediate;
+
+		bool m_handlingRESET = false;
+		bool m_handlingNMI = false;
+		bool m_handlingIRQ = false;
 	};
 }
\ No newline at end of file
diff --git a/M6502/src/mos6502.cpp b/M6502/src/mos6502.cpp
index 9b7f966..d41c0de 100644
--- a/M6502/src/mos6502.cpp
+++ b/M6502/src/mos6502.cpp
@@ -24,6 +24,7 @@ int EightBit::MOS6502::step() {
 	if (LIKELY(powered())) {
 		if (UNLIKELY(lowered(SO())))
 			handleSO();
+		opcode() = fetchByte();
 		if (UNLIKELY(lowered(HALT())))
 			handleHALT();
 		else if (UNLIKELY(lowered(RESET())))
@@ -32,8 +33,7 @@ int EightBit::MOS6502::step() {
 			handleNMI();
 		else if (UNLIKELY(lowered(IRQ()) && !interruptMasked()))
 			handleIRQ();
-		else
-			Processor::execute(fetchByte());
+		execute();
 	}
 	ExecutedInstruction.fire(*this);
 	return cycles();
@@ -47,36 +47,44 @@ void EightBit::MOS6502::handleSO() {
 }
 
 void EightBit::MOS6502::handleHALT() {
-	Processor::execute(0xea);	// NOP
+	opcode() = 0xea;	// NOP
 }
 
 void EightBit::MOS6502::handleRESET() {
-	jump(getWordPaged(0xff, RSTvector));
 	raise(RESET());
+	m_handlingRESET = true;
+	opcode() = 0x00;	// BRK
 }
 
 
 void EightBit::MOS6502::handleNMI() {
 	raise(HALT());
-	Processor::execute(0);
 	raise(NMI());
+	m_handlingNMI = true;
+	opcode() = 0x00;	// BRK
 }
 
 void EightBit::MOS6502::handleIRQ() {
 	raise(HALT());
-	Processor::execute(0);
 	raise(INT());
+	m_handlingIRQ = true;
+	opcode() = 0x00;	// BRK
 }
 
 void EightBit::MOS6502::interrupt() {
-	const bool nmi = lowered(NMI());
-	const bool irq = lowered(IRQ());
-	const bool hardware = nmi || irq;
-	const bool software = !hardware;
-	pushWord(PC());
-	push(P() | (software ? BF : 0));
-	setFlag(P(), IF);	// Disable IRQ
-	jump(getWordPaged(0xff, nmi ? NMIvector : IRQvector));
+	uint8_t vector = RSTvector;
+	if (!m_handlingRESET) {
+		const bool nmi = m_handlingNMI;
+		const bool irq = m_handlingIRQ;
+		const bool hardware = nmi || irq;
+		const bool software = !hardware;
+		pushWord(PC());
+		push(P() | (software ? BF : 0));
+		setFlag(P(), IF);	// Disable IRQ
+		vector = nmi ? NMIvector : IRQvector;
+	}
+	jump(getWordPaged(0xff, vector));
+	m_handlingRESET = m_handlingNMI = m_handlingIRQ = false;
 }
 
 //