From 21e8360dc1e5d2c46bf643d892f2c9896cccf061 Mon Sep 17 00:00:00 2001
From: Adrian Conlon <Adrian.conlon@gmail.com>
Date: Fri, 24 Aug 2018 12:14:14 +0100
Subject: [PATCH] First stab at interrupt handling on the 6809 processor.

Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
---
 MC6809/inc/mc6809.h   |  6 ++++++
 MC6809/src/mc6809.cpp | 40 ++++++++++++++++++++++++++++++++++++++--
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/MC6809/inc/mc6809.h b/MC6809/inc/mc6809.h
index 05e373d..8fe0c36 100644
--- a/MC6809/inc/mc6809.h
+++ b/MC6809/inc/mc6809.h
@@ -122,6 +122,12 @@ namespace EightBit {
 		void execute10(uint8_t opcode);
 		void execute11(uint8_t opcode);
 
+		// Interrupt handlers
+
+		void handleNMI();
+		void handleIRQ();
+		void handleFIRQ();
+
 		// Register selection for "indexed"
 		register16_t& RR(int which);
 
diff --git a/MC6809/src/mc6809.cpp b/MC6809/src/mc6809.cpp
index bf4a9e0..bf9a5a6 100644
--- a/MC6809/src/mc6809.cpp
+++ b/MC6809/src/mc6809.cpp
@@ -13,19 +13,55 @@ int EightBit::mc6809::step() {
 	if (LIKELY(powered())) {
 		m_prefix10 = m_prefix11 = false;
 		ExecutingInstruction.fire(*this);
-		return execute(fetchByte());
+		if (lowered(NMI()))
+			handleNMI();
+		else if (lowered(FIRQ()) && !(CC() & FF))
+			handleFIRQ();
+		else if (lowered(IRQ()) && !(CC() & IF))
+			handleIRQ();
+		else
+			execute(fetchByte());
 		ExecutedInstruction.fire(*this);
 	}
 	return cycles();
 }
 
+// Interrupt (etc.) handlers
+
 void EightBit::mc6809::reset() {
 	Processor::reset();
 	DP() = 0;	// Reestablish zero page
-	CC() |= (IF & FF);	// Disable interrupts
+	CC() |= (IF & FF);	// Disable IRQ and FIRQ
 	jump(getWordPaged(0xff, RESETvector));
 }
 
+void EightBit::mc6809::handleNMI() {
+	raise(NMI());
+	addCycles(21);
+	saveEntireRegisterState();
+	jump(getWordPaged(0xff, NMIvector));
+}
+
+void EightBit::mc6809::handleIRQ() {
+	raise(IRQ());
+	addCycles(21);
+	saveEntireRegisterState();
+	CC() |= IF;		// Disable IRQ
+	jump(getWordPaged(0xff, IRQvector));
+}
+
+void EightBit::mc6809::handleFIRQ() {
+	addCycles(12);
+	raise(FIRQ());
+	CC() &= ~EF;	// Clear the EF flag. i.e. this only saves PC and CC
+	pushWordS(PC());
+	pushS(CC());
+	CC() |= (IF & FF);	// Disable IRQ and FIRQ
+	jump(getWordPaged(0xff, FIRQvector));
+}
+
+//
+
 int EightBit::mc6809::execute(uint8_t opcode) {
 	const bool prefixed = m_prefix10 || m_prefix11;
 	if (LIKELY(!prefixed)) {