From 15e1258f409062b32369050a516f8b52b34b5bbb Mon Sep 17 00:00:00 2001
From: Adrian Conlon <Adrian.conlon@gmail.com>
Date: Sun, 19 Aug 2018 00:55:59 +0100
Subject: [PATCH] Rearrange the 6809 code such that I can fire memory events.

Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
---
 MC6809/inc/mc6809.h   | 32 +++++++++++++++++++++++++-------
 MC6809/src/mc6809.cpp | 15 ++++++++-------
 inc/Bus.h             |  1 +
 3 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/MC6809/inc/mc6809.h b/MC6809/inc/mc6809.h
index 13d2f39..da98da1 100644
--- a/MC6809/inc/mc6809.h
+++ b/MC6809/inc/mc6809.h
@@ -71,9 +71,10 @@ namespace EightBit {
 		const uint8_t SWI3vector = 0xf2;
 		const uint8_t RESERVEDvector = 0xf0;
 
-		uint8_t& AM_direct() {
+		//
+
+		void Address_direct() {
 			BUS().ADDRESS() = register16_t(fetchByte(), DP());
-			return BUS().reference();
 		}
 
 		register16_t& RR(int which) {
@@ -93,7 +94,7 @@ namespace EightBit {
 			}
 		}
 
-		uint8_t& AM_indexed() {
+		void Address_indexed() {
 			const auto type = fetchByte();
 			auto& rr = RR(type & (Bit6 | Bit5));
 			switch (type & Bit7) {
@@ -167,16 +168,33 @@ namespace EightBit {
 			default:
 				UNREACHABLE;
 			}
-			return BUS().reference();
 		}
 
-		uint8_t& AM_extended() {
+		void Address_extended() {
 			BUS().ADDRESS() = fetchWord();
-			return BUS().reference();
 		}
 
+		//
+
+		uint8_t AM_direct() {
+			Address_direct();
+			return BUS().read();
+		}
+
+		uint8_t AM_indexed() {
+			Address_indexed();
+			return BUS().read();
+		}
+
+		uint8_t AM_extended() {
+			AM_extended();
+			return BUS().read();
+		}
+
+		//
+
 		void abx();
-		void neg(uint8_t& operand);
+		uint8_t neg(uint8_t operand);
 
 		register16_t m_d;
 		register16_t m_x;
diff --git a/MC6809/src/mc6809.cpp b/MC6809/src/mc6809.cpp
index 4374e79..8eac25a 100644
--- a/MC6809/src/mc6809.cpp
+++ b/MC6809/src/mc6809.cpp
@@ -31,14 +31,14 @@ int EightBit::mc6809::execute(uint8_t cell) {
 	switch (cell) {
 
 	// ABX
-	case 0x3a:	addCycles(3);	abx();				break;		// ABX (inherent)
+	case 0x3a:	addCycles(3);	abx();								break;		// ABX (inherent)
 
 	// NEG
-	case 0x00:	addCycles(6);	neg(AM_direct());	break;		// NEG (direct)
-	case 0x40:	addCycles(2);	neg(A());			break;		// NEG (NEGA, inherent)
-	case 0x50:	addCycles(2);	neg(B());			break;		// NEG (NEGB, inherent)
-	case 0x60:	addCycles(6);	neg(AM_indexed());	break;		// NEG (indexed)
-	case 0x70:	addCycles(7);	neg(AM_extended());	break;		// NEG (extended)
+	case 0x00:	addCycles(6);	BUS().write(neg(AM_direct()));		break;		// NEG (direct)
+	case 0x40:	addCycles(2);	A() = neg(A());						break;		// NEG (NEGA, inherent)
+	case 0x50:	addCycles(2);	B() = neg(B());						break;		// NEG (NEGB, inherent)
+	case 0x60:	addCycles(6);	BUS().write(neg(AM_indexed()));		break;		// NEG (indexed)
+	case 0x70:	addCycles(7);	BUS().write(neg(AM_extended()));	break;		// NEG (extended)
 
 	default:
 		ASSUME(false);
@@ -54,11 +54,12 @@ void EightBit::mc6809::abx() {
 	X() += B();
 }
 
-void EightBit::mc6809::neg(uint8_t& operand) {
+uint8_t EightBit::mc6809::neg(uint8_t operand) {
 	setFlag(CC(), VF, operand == Bit7);
 	const register16_t result = 0 - operand;
 	operand = result.low;
 	setFlag(CC(), NF, operand & Bit7);
 	setFlag(CC(), ZF, operand == 0);
 	setFlag(CC(), CF, result.word & Bit8);
+	return operand;
 }
\ No newline at end of file
diff --git a/inc/Bus.h b/inc/Bus.h
index e613a77..9ee8f56 100644
--- a/inc/Bus.h
+++ b/inc/Bus.h
@@ -43,6 +43,7 @@ namespace EightBit {
 			write(value);
 		}
 
+	protected:
 		virtual uint8_t& reference(uint16_t address) = 0;
 		uint8_t& reference() { return reference(ADDRESS().word); }