Name MSW bits.

InstructionSets/x86/Implementation/LoadStore.hpp

@@ -10,7 +10,8 @@
 
 #include "InstructionSets/x86/AccessType.hpp"
 #include "InstructionSets/x86/Descriptors.hpp"
-#include "InstructionSets/x86/Mode.hpp"
+#include "InstructionSets/x86/Descriptors.hpp"
+#include "InstructionSets/x86/MachineStatus.hpp"
 
 #include <utility>
 
@@ -93,13 +94,10 @@ void lmsw(
 	ContextT &context
 ) {
 	context.registers.set_msw(source);
-	if(source & 1) {
+	if(source & MachineStatus::ProtectedModeEnable) {
 		context.memory.set_mode(Mode::Protected286);
 		context.segments.set_mode(Mode::Protected286);
 	}
-
-	// TODO: all other bits. Anything?
-	assert(!(source & ~1));
 }
 
 template <DescriptorTable table, typename AddressT, typename InstructionT, typename ContextT>

InstructionSets/x86/Implementation/PerformImplementation.hpp

@@ -13,8 +13,10 @@
 #include "BCD.hpp"
 #include "FlowControl.hpp"
 #include "InOut.hpp"
+#include "Interrupts.hpp"
 #include "LoadStore.hpp"
 #include "Logical.hpp"
+#include "MachineStatus.hpp"
 #include "Repetition.hpp"
 #include "Resolver.hpp"
 #include "ShiftRoll.hpp"
@@ -179,12 +181,22 @@ template <
 		default:
 			assert(false);
 
+		case Operation::NOP:	return;
+
 		case Operation::Invalid:
 			if constexpr (!uses_8086_exceptions(ContextT::model)) {
 				throw Exception(Interrupt::InvalidOpcode);
 			}
+		return;
+
 		case Operation::ESC:
-		case Operation::NOP:	return;
+			if constexpr (!uses_8086_exceptions(ContextT::model)) {
+				const auto should_throw = context.registers.msw() & MachineStatus::EmulateProcessorExtension;
+				if(should_throw) {
+					throw Exception(Interrupt::DeviceNotAvailable);
+				}
+			}
+		return;
 
 		case Operation::AAM:
 			Primitive::aam(context.registers.axp(), uint8_t(instruction.operand()), context);

InstructionSets/x86/Interrupts.hpp

@@ -22,7 +22,7 @@ enum Interrupt {
 	BoundRangeExceeded			= 5,
 
 	//
-	// Added by the 80286
+	// Added by the 80286.
 	//
 	InvalidOpcode				= 6,
 	DeviceNotAvailable			= 7,
@@ -35,7 +35,7 @@ enum Interrupt {
 	FloatingPointException		= 16,
 
 	//
-	// Added by the 80286
+	// Added by the 80286.
 	//
 	PageFault					= 14,
 	AlignmentCheck				= 17,

InstructionSets/x86/MachineStatus.hpp

@@ -0,0 +1,26 @@
+//
+//  MachineStatus.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 30/03/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include <cstdint>
+
+namespace InstructionSet::x86 {
+
+enum MachineStatus: uint16_t {
+	//
+	// 80286 state.
+	//
+	ProtectedModeEnable = 1 << 0,
+	MonitorProcessorExtension = 1 << 1,
+	EmulateProcessorExtension = 1 << 2,
+	TaskSwitched = 1 << 3,
+};
+
+}
+

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -1761,6 +1761,7 @@
 		4B85322E2277ABDD00F26553 /* tos100.trace.txt.gz */ = {isa = PBXFileReference; lastKnownFileType = archive.gzip; path = tos100.trace.txt.gz; sourceTree = "<group>"; };
 		4B8671EA2D8B40D8009E1610 /* Descriptors.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Descriptors.hpp; sourceTree = "<group>"; };
 		4B8671EB2D8FABA0009E1610 /* Mode.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Mode.hpp; sourceTree = "<group>"; };
+		4B8671EC2D99BE2C009E1610 /* MachineStatus.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = MachineStatus.hpp; sourceTree = "<group>"; };
 		4B86E2591F8C628F006FAA45 /* Keyboard.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Keyboard.cpp; sourceTree = "<group>"; };
 		4B86E25A1F8C628F006FAA45 /* Keyboard.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Keyboard.hpp; sourceTree = "<group>"; };
 		4B8805EE1DCFC99C003085B1 /* Acorn.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; name = Acorn.cpp; path = Parsers/Acorn.cpp; sourceTree = "<group>"; };
@@ -5371,6 +5372,7 @@
 				42437B342ACF02A9006DFED1 /* Flags.hpp */,
 				4BEDA3DB25B2588F000C2DBD /* Instruction.hpp */,
 				42437B392AD07465006DFED1 /* Interrupts.hpp */,
+				4B8671EC2D99BE2C009E1610 /* MachineStatus.hpp */,
 				4B8671EB2D8FABA0009E1610 /* Mode.hpp */,
 				4BE3C69527CBC540000EAD28 /* Model.hpp */,
 				42437B352ACF0AA2006DFED1 /* Perform.hpp */,