Add an "UnusedMemory" class to better allow "gaps" in the memory map.

Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>

LR35902/inc/GameBoyBus.h

@@ -7,6 +7,7 @@
 #include <Ram.h>
 #include <Bus.h>
 #include <Register.h>
+#include <UnusedMemory.h>
 
 #include "LR35902.h"
 #include "IoRegisters.h"
@@ -63,10 +64,10 @@ namespace EightBit {
 			std::vector<Rom> m_gameRomBanks;				// 0x0000 - 0x3fff, 0x4000 - 0x7fff (switchable)
 			Ram m_videoRam = 0x2000;						// 0x8000 - 0x9fff
 			std::vector<Ram> m_ramBanks;					// 0xa000 - 0xbfff (switchable)
-			Rom m_unmapped2000 = 0x2000;		// 0xa000 - 0xbfff
+			UnusedMemory m_unmapped2000 = { 0x2000, 0xff };	// 0xa000 - 0xbfff
 			Ram m_lowInternalRam = 0x2000;					// 0xc000 - 0xdfff (mirrored at 0xe000)
 			Ram m_oamRam = 0xa0;							// 0xfe00 - 0xfe9f
-			Rom m_unmapped60 = 0x60;			// 0xfea0 - 0xfeff
+			UnusedMemory m_unmapped60 = { 0x60, 0xff };		// 0xfea0 - 0xfeff
 			IoRegisters m_ioPorts;							// 0xff00 - 0xff7f
 			Ram m_highInternalRam = 0x80;					// 0xff80 - 0xffff
 

LR35902/src/GameBoyBus.cpp

@@ -6,18 +6,6 @@ EightBit::GameBoy::Bus::Bus() noexcept
 : m_cpu(*this),
   m_ioPorts(*this) {
 	WrittenByte.connect(std::bind(&GameBoy::Bus::Bus_WrittenByte, this, std::placeholders::_1));
-
-	{
-		std::vector<uint8_t> content(m_unmapped2000.size());
-		std::fill(content.begin(), content.end(), 0xff);
-		m_unmapped2000.load(content);
-	}
-
-	{
-		std::vector<uint8_t> content(m_unmapped60.size());
-		std::fill(content.begin(), content.end(), 0xff);
-		m_unmapped60.load(content);
-	}
 }
 
 void EightBit::GameBoy::Bus::reset() {

MC6809/test/Board.cpp

@@ -5,9 +5,6 @@ Board::Board(const Configuration& configuration)
 : m_configuration(configuration),
   m_cpu(EightBit::mc6809(*this)),
   m_disassembler(*this, m_cpu) {
-	std::vector<uint8_t> content(m_unused2000.size());
-	std::fill(content.begin(), content.end(), 0xff);
-	m_unused2000.load(content);
 }
 
 void Board::initialise() {

MC6809/test/Board.h

@@ -9,6 +9,7 @@
 #include <mc6809.h>
 #include <Disassembly.h>
 #include <MC6850.h>
+#include <UnusedMemory.h>
 
 class Board : public EightBit::Bus {
 public:
@@ -25,7 +26,7 @@ protected:
 private:
 	const Configuration& m_configuration;
 	EightBit::Ram m_ram = 0x8000;							// 0000 - 7FFF, 32K RAM
-	EightBit::Rom m_unused2000 = 0x2000;	// 8000 - 9FFF, 8K unused
+	EightBit::UnusedMemory m_unused2000 = { 0x2000, 0xff };	// 8000 - 9FFF, 8K unused
 	EightBit::Ram m_io = 0x2000;							// A000 - BFFF, 8K serial interface, minimally decoded
 	EightBit::Rom m_rom = 0x4000;							// C000 - FFFF, 16K ROM
 

inc/MemoryInterface.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <cstdint>
+#include <fstream>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+namespace EightBit {
+	class MemoryInterface {
+	public:
+		virtual size_t size() const = 0;
+		virtual uint8_t peek(uint16_t address) const = 0;
+
+		virtual uint8_t& reference(uint16_t) {
+			throw new std::logic_error("Reference operation not allowed.");
+		}
+
+		virtual int load(std::ifstream& file, int writeOffset = 0, int readOffset = 0, int limit = -1) = 0;
+		virtual int load(const std::string& path, int writeOffset = 0, int readOffset = 0, int limit = -1) = 0;
+		virtual int load(const std::vector<uint8_t>& bytes, int writeOffset = 0, int readOffset = 0, int limit = -1) = 0;
+
+	protected:
+		virtual void poke(uint16_t address, uint8_t value) = 0;
+	};
+}

inc/UnusedMemory.h

@@ -0,0 +1,40 @@
+#pragma once
+
+#include "MemoryInterface.h"
+
+namespace EightBit {
+	class UnusedMemory final : public MemoryInterface {
+	public:
+		UnusedMemory(const size_t size, const uint8_t value)
+		: m_size(size), m_value(value) {}
+		virtual ~UnusedMemory() = default;
+
+		virtual size_t size() const final { return m_size; }
+		virtual uint8_t peek(uint16_t address) const final { return m_value; }
+
+		virtual uint8_t& reference(uint16_t) {
+			throw new std::logic_error("Reference operation not allowed.");
+		}
+
+		virtual int load(std::ifstream& file, int writeOffset = 0, int readOffset = 0, int limit = -1) final {
+			throw new std::logic_error("load operation not allowed.");
+		}
+
+		virtual int load(const std::string& path, int writeOffset = 0, int readOffset = 0, int limit = -1) final {
+			throw new std::logic_error("load operation not allowed.");
+		}
+		
+		virtual int load(const std::vector<uint8_t>& bytes, int writeOffset = 0, int readOffset = 0, int limit = -1) final {
+			throw new std::logic_error("load operation not allowed.");
+		}
+
+	protected:
+		virtual void poke(uint16_t address, uint8_t value) {
+			throw new std::logic_error("Poke operation not allowed.");
+		}
+
+	private:
+		size_t m_size;
+		uint8_t m_value;
+	};
+}

src/Bus.cpp

@@ -93,6 +93,5 @@ uint8_t& EightBit::Bus::reference(const uint16_t address) {
 	const uint16_t offset = (address - mapped.begin) & mapped.mask;
 	if (mapped.access == MemoryMapping::ReadOnly)
 		return DATA() = mapped.memory.peek(offset);
-	Ram& ram = (Ram&)(mapped.memory);
-	return ram.reference(offset);
+	return mapped.memory.reference(offset);
 }

src/EightBit.vcxproj

@@ -156,6 +156,7 @@
     <ClInclude Include="..\inc\Register.h" />
     <ClInclude Include="..\inc\Signal.h" />
     <ClInclude Include="..\inc\TestHarness.h" />
+    <ClInclude Include="..\inc\UnusedMemory.h" />
     <ClInclude Include="stdafx.h" />
   </ItemGroup>
   <ItemGroup>

src/EightBit.vcxproj.filters

@@ -62,6 +62,9 @@
     <ClInclude Include="..\inc\MemoryInterface.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="..\inc\UnusedMemory.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="stdafx.cpp">