Finished up configuration UI. Config is now persisted to a configuration file. Small fixes to UDP encapsulation to ignore packets coming from the same host. Small fix for PInvoke for high res timer.

2026-02-15 20:26:56 +00:00 · 2016-03-02 17:31:19 -08:00
parent c73fb66dee
commit c48e530cbe
19 changed files with 701 additions and 207 deletions
--- a/Contralto/AltoSystem.cs
+++ b/Contralto/AltoSystem.cs
@@ -65,10 +65,7 @@ namespace Contralto
            _cpu.Reset();
            _ethernetController.Reset();

-            UCodeMemory.Reset();
-
-            // Force the boot keys on reset.
-            PressBootKeys();
+            UCodeMemory.Reset();            
        }

        /// <summary>
@@ -126,18 +123,20 @@ namespace Contralto
            _diskController.Drives[drive].UnloadPack();
        }

-        public void PressBootKeys()
+        public void PressBootKeys(AlternateBootType bootType)
        {
-            //
-            // Press bootkeys if the user has specified a boot combination.
-            //
-            if (Configuration.EthernetBootEnabled)
+            switch(bootType)
            {
-                _keyboard.PressBootKeys(Configuration.BootAddress, true);
+                case AlternateBootType.Disk:
+                    _keyboard.PressBootKeys(Configuration.BootAddress, false);
+                    break;
+
+                case AlternateBootType.Ethernet:
+                    _keyboard.PressBootKeys(Configuration.BootFile, true);
+                    break;
            }
        }

-
        public AltoCPU CPU
        {
            get { return _cpu; }
--- a/Contralto/Configuration.cs
+++ b/Contralto/Configuration.cs
@@ -41,6 +41,18 @@ namespace Contralto
        /// Encapsulate frames inside UDP datagrams on the host interface.
        /// </summary>
        UDPEncapsulation,
+
+        /// <summary>
+        /// No encapsulation; sent packets are dropped on the floor and no packets are received.
+        /// </summary>
+        None,
+    }
+
+    public enum AlternateBootType
+    {
+        None,
+        Disk,
+        Ethernet,
    }

    /// <summary>
@@ -53,8 +65,9 @@ namespace Contralto
            // Initialize things to defaults.            
            HostAddress = 0x22;

-            EthernetBootEnabled = false;
+            AlternateBootType = AlternateBootType.Disk;
            BootAddress = 0;
+            BootFile = 0;

            SystemType = SystemType.TwoKRom;

@@ -98,18 +111,23 @@ namespace Contralto
        /// <summary>
        /// The type of interface to use to host networking.
        /// </summary>
-        public static PacketInterfaceType HostPacketInterfaceType;
+        public static PacketInterfaceType HostPacketInterfaceType;        

        /// <summary>
-        /// Whether to enable Ethernet boot at reset
+        /// The type of Alternate Boot to apply
        /// </summary>
-        public static bool EthernetBootEnabled;
+        public static AlternateBootType AlternateBootType;

        /// <summary>
-        /// The address/file to boot at reset
+        /// The address to boot at reset for a disk alternate boot
        /// </summary>
        public static ushort BootAddress;

+        /// <summary>
+        /// The file to boot at reset for an ethernet alternate boot
+        /// </summary>
+        public static ushort BootFile;
+
        /// <summary>
        /// Whether to render the display "interlaced" or not.
        /// </summary>
@@ -140,7 +158,7 @@ namespace Contralto
                    while (!configStream.EndOfStream)
                    {
                        lineNumber++;
-                        string line = configStream.ReadLine().ToLowerInvariant().Trim();
+                        string line = configStream.ReadLine().Trim();

                        if (string.IsNullOrEmpty(line))
                        {
@@ -161,7 +179,7 @@ namespace Contralto

                        try
                        {
-                            switch (parameter)
+                            switch (parameter.ToLowerInvariant())
                            {
                                case "drive0image":
                                    Drive0Image = value;
@@ -187,14 +205,18 @@ namespace Contralto
                                    HostPacketInterfaceType = (PacketInterfaceType)Enum.Parse(typeof(PacketInterfaceType), value, true);
                                    break;

-                                case "ethernetbootenabled":
-                                    EthernetBootEnabled = bool.Parse(value);
+                                case "alternateboottype":
+                                    AlternateBootType = (AlternateBootType)Enum.Parse(typeof(AlternateBootType), value, true);
                                    break;

                                case "bootaddress":
                                    BootAddress = Convert.ToUInt16(value, 8);
                                    break;

+                                case "bootfile":
+                                    BootFile = Convert.ToUInt16(value, 8);
+                                    break;
+
                                case "interlacedisplay":
                                    InterlaceDisplay = bool.Parse(value);
                                    break;
@@ -251,8 +273,9 @@ namespace Contralto
                    }

                    configStream.WriteLine("HostPacketInterfaceType {0}", HostPacketInterfaceType);
-                    configStream.WriteLine("EthernetBootEnabled {0}", EthernetBootEnabled);
+                    configStream.WriteLine("AlternateBootType {0}", AlternateBootType);
                    configStream.WriteLine("BootAddress {0}", Conversion.ToOctal(BootAddress));
+                    configStream.WriteLine("BootFile {0}", Conversion.ToOctal(BootFile));
                    configStream.WriteLine("InterlaceDisplay {0}", InterlaceDisplay);
                    configStream.WriteLine("ThrottleSpeed {0}", ThrottleSpeed);
                }
--- a/Contralto/Disk/allgames.dsk
+++ b/Contralto/Disk/allgames.dsk
--- a/Contralto/Disk/diag.dsk
+++ b/Contralto/Disk/diag.dsk
--- a/Contralto/ExecutionController.cs
+++ b/Contralto/ExecutionController.cs
@@ -23,9 +23,10 @@ namespace Contralto

        }        

-        public void StartExecution()
+        public void StartExecution(AlternateBootType bootType)
        {
            StartAltoExecutionThread();
+            _system.PressBootKeys(bootType);
        }

        public void StopExecution()
@@ -39,7 +40,7 @@ namespace Contralto
            }
        }

-        public void Reset()
+        public void Reset(AlternateBootType bootType)
        {
            bool running = IsRunning;

@@ -47,13 +48,13 @@ namespace Contralto
            {
                StopExecution();
            }
-            _system.Reset();
+            _system.Reset();            
+            _system.PressBootKeys(bootType);            

            if (running)
            {
-                StartExecution();
+                StartExecution(AlternateBootType.None);
            }
-
        }       

        public bool IsRunning
--- a/Contralto/HighResTimer.cs
+++ b/Contralto/HighResTimer.cs
@@ -62,7 +62,7 @@ namespace Contralto
        public static extern bool DeleteTimerQueue(IntPtr hTimerQueue, IntPtr hCompletionEvent);

        [DllImport("kernel32.dll", EntryPoint = "CreateTimerQueueTimer")]
-        public static extern bool CreateTimerQueueTimer(out IntPtr phNewTimer, IntPtr hTimerQueue, IntPtr Callback, IntPtr Parameter, UInt32 DueTime, UInt32 Period, ulong Flags);
+        public static extern bool CreateTimerQueueTimer(out IntPtr phNewTimer, IntPtr hTimerQueue, IntPtr Callback, IntPtr Parameter, UInt32 DueTime, UInt32 Period, uint Flags);

        [DllImport("kernel32.dll", EntryPoint = "ChangeTimerQueueTimer")]
        public static extern bool ChangeTimerQueueTimer(IntPtr hTimerQueue, IntPtr hTimer, UInt32 DueTime, UInt32 Period);
--- a/Contralto/IO/EthernetController.cs
+++ b/Contralto/IO/EthernetController.cs
@@ -21,25 +21,32 @@ namespace Contralto.IO
            Reset();

            _fifoTransmitWakeupEvent = new Event(_fifoTransmitDuration, null, OutputFifoCallback);
-            
+

            // Attach real Ethernet device if user has specified one, otherwise leave unattached; output data
            // will go into a bit-bucket.
-            switch(Configuration.HostPacketInterfaceType)
+            try
            {
-                case PacketInterfaceType.UDPEncapsulation:
-                    _hostInterface = new UDPEncapsulation(Configuration.HostPacketInterfaceName);
-                    _hostInterface.RegisterReceiveCallback(OnHostPacketReceived);
-                    break;
+                switch (Configuration.HostPacketInterfaceType)
+                {
+                    case PacketInterfaceType.UDPEncapsulation:
+                        _hostInterface = new UDPEncapsulation(Configuration.HostPacketInterfaceName);
+                        _hostInterface.RegisterReceiveCallback(OnHostPacketReceived);
+                        break;

-                case PacketInterfaceType.EthernetEncapsulation:
-                    _hostInterface = new HostEthernetEncapsulation(Configuration.HostPacketInterfaceName);
-                    _hostInterface.RegisterReceiveCallback(OnHostPacketReceived);
-                    break;
+                    case PacketInterfaceType.EthernetEncapsulation:
+                        _hostInterface = new HostEthernetEncapsulation(Configuration.HostPacketInterfaceName);
+                        _hostInterface.RegisterReceiveCallback(OnHostPacketReceived);
+                        break;

-                default:
-                    _hostInterface = null;
-                    break;
+                    default:
+                        _hostInterface = null;
+                        break;
+                }
+            }
+            catch
+            {
+                _hostInterface = null;
            }

            // More words than the Alto will ever send.
@@ -359,7 +366,9 @@ namespace Contralto.IO
            }
            else
            {
-                Log.Write(LogType.Error, LogComponent.EthernetPacket, "Packet queue has reached its limit of {0} packets, dropping incoming packet.", _maxQueuedPackets);
+                Log.Write(LogType.Error, LogComponent.EthernetPacket, "Input packet queue has reached its limit of {0} packets, dropping oldest packet.", _maxQueuedPackets);
+                _nextPackets.Dequeue();
+                _nextPackets.Enqueue(data);
            }

            _receiverLock.ExitWriteLock();            
@@ -367,7 +376,7 @@ namespace Contralto.IO

        /// <summary>
        /// Runs the input state machine.  This runs periodically (as scheduled by the Scheduler) and:
-        ///   1) Drops incoming packets if the interface is off
+        ///   1) Ignores incoming packets if the receiver is off.
        ///   2) Pulls incoming packets from the queue if the interface is active
        ///   3) Reads words from incoming packets into the controller's FIFO        
        /// </summary>
@@ -379,13 +388,16 @@ namespace Contralto.IO
            switch(_inputState)
            {
                case InputState.ReceiverOff:
-                    // Receiver is off, if we have any incoming packets, drop the first.
+                    // Receiver is off, if we have any incoming packets, they are ignored.
+                    // TODO: would it make sense to expire really old packets (say more than a couple of seconds old)
+                    // so that the receiver doesn't pick up ancient history the next time it runs?
+                    // We already cycle out packets as new ones come in, so this would only be an issue on very quiet networks.
+                    // (And even then I don't know if it's really an issue.)
                    _receiverLock.EnterReadLock();

                    if (_nextPackets.Count > 0)
                    {
-                        _nextPackets.Dequeue();
-                        Log.Write(LogComponent.EthernetPacket, "Receiver is off, dropped incoming packet from packet queue.");
+                        Log.Write(LogComponent.EthernetPacket, "Receiver is off, ignoring incoming packet from packet queue.");
                    }
                    _receiverLock.ExitReadLock();
                    break;
--- a/Contralto/IO/HostEthernet.cs
+++ b/Contralto/IO/HostEthernet.cs
@@ -0,0 +1,281 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using PcapDotNet.Base;
+using PcapDotNet.Core;
+using PcapDotNet.Core.Extensions;
+using PcapDotNet.Packets;
+using PcapDotNet.Packets.Ethernet;
+using System.IO;
+using Contralto.Logging;
+using System.Threading;
+
+namespace Contralto.IO
+{
+
+    public struct EthernetInterface
+    {
+        public EthernetInterface(string name, string description, MacAddress macAddress)
+        {
+            Name = name;
+            Description = description;
+            MacAddress = macAddress;
+        }
+
+        public static List<EthernetInterface> EnumerateDevices()
+        {
+            List<EthernetInterface> interfaces = new List<EthernetInterface>();
+
+            foreach (LivePacketDevice device in LivePacketDevice.AllLocalMachine)
+            {
+                interfaces.Add(new EthernetInterface(device.Name, device.Description, device.GetMacAddress()));
+            }
+
+            return interfaces;
+        }
+
+        public string Name;
+        public string Description;
+        public MacAddress MacAddress;
+    }
+
+    public delegate void ReceivePacketDelegate(MemoryStream data);
+
+    /// <summary>
+    /// Implements the logic for encapsulating a 3mbit ethernet packet into a 10mb packet and sending it over an actual
+    /// interface controlled by the host operating system.
+    /// 
+    /// This uses PCap.NET to do the dirty work.
+    /// </summary>
+    public class HostEthernet
+    {
+        public HostEthernet(EthernetInterface iface)
+        {
+            AttachInterface(iface);
+        }
+
+        public HostEthernet(string name)
+        {
+            // Find the specified device by name
+            List<EthernetInterface> interfaces = EthernetInterface.EnumerateDevices();
+
+            foreach (EthernetInterface i in interfaces)
+            {
+                if (name == i.Name)
+                {
+                    AttachInterface(i);
+                    return;
+                }
+            }
+
+            throw new InvalidOperationException("Specified ethernet interface does not exist.");
+        }
+
+        public void RegisterReceiveCallback(ReceivePacketDelegate callback)
+        {
+            _callback = callback;
+
+            // Now that we have a callback we can start receiving stuff.
+            Open(true /* promiscuous */, int.MaxValue);
+            BeginReceive();
+        }
+
+
+        /// <summary>
+        /// Sends an array of bytes over the ethernet as a 3mbit packet encapsulated in a 10mbit packet.
+        /// </summary>
+        /// <param name="packet"></param>
+        /// <param name="hostId"></param>
+        public void Send(ushort[] packet, int length)
+        {
+            // Sanity check.
+            if (length < 1)
+            {
+                throw new InvalidOperationException("Raw packet data must contain at least two bytes for addressing.");
+            }
+
+
+            //
+            // Outgoing packet contains 1 extra word (2 bytes) containing
+            // the prepended packet length (one word)            
+            byte[] packetBytes = new byte[length * 2 + 2];
+
+            //
+            // First two bytes include the length of the 3mbit packet; since 10mbit packets have a minimum length of 46 
+            // bytes, and 3mbit packets have no minimum length this is necessary so the receiver can pull out the 
+            // correct amount of data.
+            //
+            packetBytes[0] = (byte)(length);
+            packetBytes[1] = (byte)((length) >> 8);
+
+            //
+            // Do this annoying dance to stuff the ushorts into bytes because this is C#.
+            //
+            for (int i = 0; i < length; i++)
+            {
+                packetBytes[i * 2 + 2] = (byte)(packet[i]);
+                packetBytes[i * 2 + 3] = (byte)(packet[i] >> 8);
+            }
+
+            //
+            // Grab the source and destination host addresses from the packet we're sending
+            // and build 10mbit versions.
+            //
+            byte destinationHost = packetBytes[3];
+            byte sourceHost = packetBytes[2];
+
+            Log.Write(LogComponent.HostEthernet, "Sending packet; source {0} destination {1}, length {2} words.",
+                Conversion.ToOctal(sourceHost),
+                Conversion.ToOctal(destinationHost),
+                length);
+
+            MacAddress destinationMac = Get10mbitDestinationMacFrom3mbit(destinationHost);
+            MacAddress sourceMac = new MacAddress((UInt48)(_10mbitMACPrefix | Configuration.HostAddress));
+
+            // Build the outgoing packet; place the source/dest addresses, type field and the raw data.                
+            EthernetLayer ethernetLayer = new EthernetLayer
+            {
+                Source = sourceMac,
+                Destination = destinationMac,
+                EtherType = (EthernetType)_3mbitFrameType,
+            };
+
+            PayloadLayer payloadLayer = new PayloadLayer
+            {
+                Data = new Datagram(packetBytes),
+            };
+
+            PacketBuilder builder = new PacketBuilder(ethernetLayer, payloadLayer);
+
+            // Send it over the 'net!
+            _communicator.SendPacket(builder.Build(DateTime.Now));
+
+            Log.Write(LogComponent.HostEthernet, "Encapsulated 3mbit packet sent.");
+        }
+
+        private void ReceiveCallback(Packet p)
+        {
+            //
+            // Filter out packets intended for the emulator, forward them on, drop everything else.
+            //
+            if ((int)p.Ethernet.EtherType == _3mbitFrameType &&                                               // encapsulated 3mbit frames
+                ((p.Ethernet.Destination.ToValue() & 0xffffffffff00) == _10mbitMACPrefix ||                     // addressed to any emulator OR
+                 p.Ethernet.Destination.ToValue() == _10mbitBroadcast) &&                                       // broadcast
+                (p.Ethernet.Source.ToValue() != (UInt48)(_10mbitMACPrefix | Configuration.HostAddress)))      // and not sent by this emulator                
+            {
+                Log.Write(LogComponent.HostEthernet, "Received encapsulated 3mbit packet.");
+                _callback(p.Ethernet.Payload.ToMemoryStream());
+            }
+            else
+            {
+                // Not for us, discard the packet.                
+            }
+        }
+
+        private void AttachInterface(EthernetInterface iface)
+        {
+            _interface = null;
+
+            // Find the specified device by name
+            foreach (LivePacketDevice device in LivePacketDevice.AllLocalMachine)
+            {
+                if (device.Name == iface.Name && device.GetMacAddress() == iface.MacAddress)
+                {
+                    _interface = device;
+                    break;
+                }
+            }
+
+            if (_interface == null)
+            {
+                throw new InvalidOperationException("Requested interface not found.");
+            }
+
+            Log.Write(LogComponent.HostEthernet, "Attached to host interface {0}", iface.Name);
+        }
+
+        private void Open(bool promiscuous, int timeout)
+        {
+            _communicator = _interface.Open(65536, promiscuous ? PacketDeviceOpenAttributes.MaximumResponsiveness | PacketDeviceOpenAttributes.Promiscuous : PacketDeviceOpenAttributes.MaximumResponsiveness, timeout);
+
+            // Set this to 1 so we'll get packets as soon as they arrive, no buffering.
+            _communicator.SetKernelMinimumBytesToCopy(1);
+
+            Log.Write(LogComponent.HostEthernet, "Host interface opened and receiving packets.");
+        }
+
+        /// <summary>
+        /// Begin receiving packets, forever.
+        /// </summary>
+        private void BeginReceive()
+        {
+            // Kick off receive thread.   
+            _receiveThread = new Thread(ReceiveThread);
+            _receiveThread.Start();
+        }
+
+        private void ReceiveThread()
+        {
+            // Just call ReceivePackets, that's it.  This will never return.
+            // (probably need to make this more elegant so we can tear down the thread
+            // properly.)
+            Log.Write(LogComponent.HostEthernet, "Receiver thread started.");
+            _communicator.ReceivePackets(-1, ReceiveCallback);
+        }
+
+        private MacAddress Get10mbitDestinationMacFrom3mbit(byte destinationHost)
+        {
+            MacAddress destinationMac;
+            
+            if (destinationHost == _3mbitBroadcast)
+            {
+                // 3mbit broadcast gets translated to 10mbit broadcast
+                destinationMac = new MacAddress(_10mbitBroadcast);
+            }
+            else
+            {
+                // Check addressing table for external (non emulator) addresses;
+                // otherwise just address other emulators
+                // TODO: implement table.  Currently hardcoded address 1 to test IFS on dev machine
+                //
+                if (destinationHost == 1)
+                {
+                    destinationMac = new MacAddress((UInt48)(_ifsTestMAC));
+                }
+                else
+                {
+                    destinationMac = new MacAddress((UInt48)(_10mbitMACPrefix | destinationHost));       // emulator destination address
+                }
+            
+            }            
+
+            return destinationMac;
+        }    
+
+        private LivePacketDevice _interface;
+        private PacketCommunicator _communicator;
+        private ReceivePacketDelegate _callback;
+
+
+        // Thread used for receive
+        private Thread _receiveThread;
+
+        private const int _3mbitFrameType = 0xbeef;     // easy to identify, ostensibly unused by anything of any import        
+
+        /// <summary>
+        /// On output, these bytes are prepended to the Alto's 3mbit (1 byte) address to form a full
+        /// 6 byte Ethernet MAC.
+        /// On input, ethernet frames are checked for this prefix
+        /// </summary>
+        private UInt48 _10mbitMACPrefix = 0x0000aa010200;  // 00-00-AA is the Xerox vendor code, used just to be cute.  
+
+        private UInt48 _10mbitBroadcast = (UInt48)0xffffffffffff;
+        private const int _3mbitBroadcast = 0;
+
+        // Temporary; to be replaced with an external address mapping table
+        private UInt48 _ifsTestMAC = (UInt48)0x001060b88e3e;
+    }   
+}
--- a/Contralto/IO/HostEthernetEncapsulation.cs
+++ b/Contralto/IO/HostEthernetEncapsulation.cs
@@ -65,7 +65,7 @@ namespace Contralto.IO

            foreach (EthernetInterface i in interfaces)
            {
-                if (name == i.Name)
+                if (name == i.Description)
                {
                    AttachInterface(i);
                    return;
@@ -183,7 +183,7 @@ namespace Contralto.IO
            // Find the specified device by name
            foreach (LivePacketDevice device in LivePacketDevice.AllLocalMachine)
            {
-                if (device.Description == iface.Name)
+                if (device.Description == iface.Description)
                {
                    _interface = device;
                    break;
--- a/Contralto/IO/Keyboard.cs
+++ b/Contralto/IO/Keyboard.cs
@@ -119,8 +119,7 @@ namespace Contralto.IO
            // If we had been holding boot keys, release them now that a real user is pressing a key.
            if (_bootKeysPressed)
            {
-                Reset();
-                _bootKeysPressed = false;
+                Reset();                
            }

            AltoKeyBit bits = _keyMap[key];
--- a/Contralto/IO/UDPEncapsulation.cs
+++ b/Contralto/IO/UDPEncapsulation.cs
@@ -21,6 +21,8 @@ namespace Contralto.IO
            {
                _udpClient = new UdpClient(_udpPort, AddressFamily.InterNetwork);
                _udpClient.EnableBroadcast = true;
+                _udpClient.Client.Blocking = true;
+                _udpClient.Client.MulticastLoopback = false;

                //
                // Grab the broadcast address for the interface so that we know what broadcast address to use
@@ -31,7 +33,7 @@ namespace Contralto.IO
                IPInterfaceProperties props = null;
                foreach(NetworkInterface nic in nics)
                {
-                    if (nic.Description.ToLowerInvariant() == interfaceName.ToLowerInvariant())
+                    if (nic.Description == interfaceName)
                    {
                        props = nic.GetIPProperties();
                        break;
@@ -49,7 +51,8 @@ namespace Contralto.IO
                    // go with it.
                    if (unicast.Address.AddressFamily == AddressFamily.InterNetwork)
                    {
-                        _broadcastEndpoint = new IPEndPoint(GetBroadcastAddress(unicast.Address, unicast.IPv4Mask), _udpPort);
+                        _thisIPAddress = unicast.Address;
+                        _broadcastEndpoint = new IPEndPoint(GetBroadcastAddress(_thisIPAddress, unicast.IPv4Mask), _udpPort);
                        break;
                    }
                }
@@ -173,8 +176,12 @@ namespace Contralto.IO

                // TODO: sanitize data before handing it off.

-                Log.Write(LogComponent.HostNetworkInterface, "Received UDP-encapsulated 3mbit packet.");
-                _callback(new System.IO.MemoryStream(data));
+                // Drop our own UDP packets.
+                if (!groupEndPoint.Address.Equals(_thisIPAddress))
+                {
+                    Log.Write(LogComponent.HostNetworkInterface, "Received UDP-encapsulated 3mbit packet.");
+                    _callback(new System.IO.MemoryStream(data));
+                }
            }
        }

@@ -204,5 +211,7 @@ namespace Contralto.IO
        private UdpClient _udpClient;
        private IPEndPoint _broadcastEndpoint;

+        // The IP address (unicast address) of the interface we're using to send UDP datagrams.
+        private IPAddress _thisIPAddress;
    }   
 }
--- a/Contralto/Program.cs
+++ b/Contralto/Program.cs
@@ -21,12 +21,28 @@ namespace Contralto

            if (!String.IsNullOrEmpty(Configuration.Drive0Image))
            {
-                system.LoadDrive(0, Configuration.Drive0Image);
+                try
+                {
+                    system.LoadDrive(0, Configuration.Drive0Image);
+                }
+                catch(Exception e)
+                {
+                    Console.WriteLine("Could not load image '{0}' for drive 0.  Error '{1}'.", Configuration.Drive0Image, e.Message);
+                    system.UnloadDrive(0);
+                }
            }

            if (!String.IsNullOrEmpty(Configuration.Drive1Image))
            {
-                system.LoadDrive(1, Configuration.Drive1Image);
+                try
+                {
+                    system.LoadDrive(1, Configuration.Drive0Image);
+                }
+                catch (Exception e)
+                {
+                    Console.WriteLine("Could not load image '{0}' for drive 1.  Error '{1}'.", Configuration.Drive1Image, e.Message);
+                    system.UnloadDrive(1);
+                }
            }

            AltoWindow mainWindow = new AltoWindow();
@@ -57,7 +73,7 @@ namespace Contralto
            catch
            {
                Console.WriteLine("WARNING: WinPCAP does not appear to be properly installed.");
-                Console.WriteLine("         Ethernet functionality is disabled.");
+                Console.WriteLine("         Raw Ethernet functionality will be disabled.");
                Console.WriteLine("         Please install WinPCAP from: http://www.winpcap.org/");

                Configuration.HostRawEthernetInterfacesAvailable = false;
--- a/Contralto/UI/AlternateBootWindow.Designer.cs
+++ b/Contralto/UI/AlternateBootWindow.Designer.cs
@@ -28,45 +28,41 @@
        /// </summary>
        private void InitializeComponent()
        {
-            this.EthernetBootEnabled = new System.Windows.Forms.CheckBox();
-            this.BootFileGroup = new System.Windows.Forms.GroupBox();
+            this.EthernetBootFileGroup = new System.Windows.Forms.GroupBox();
            this.label1 = new System.Windows.Forms.Label();
            this.BootFileComboBox = new System.Windows.Forms.ComboBox();
            this.OKButton = new System.Windows.Forms.Button();
            this.CancelButton = new System.Windows.Forms.Button();
-            this.BootFileGroup.SuspendLayout();
+            this.groupBox1 = new System.Windows.Forms.GroupBox();
+            this.EthernetBootRadioButton = new System.Windows.Forms.RadioButton();
+            this.DiskBootRadioButton = new System.Windows.Forms.RadioButton();
+            this.DiskBootGroupBox = new System.Windows.Forms.GroupBox();
+            this.DiskBootAddressTextBox = new System.Windows.Forms.TextBox();
+            this.label2 = new System.Windows.Forms.Label();
+            this.EthernetBootFileGroup.SuspendLayout();
+            this.groupBox1.SuspendLayout();
+            this.DiskBootGroupBox.SuspendLayout();
            this.SuspendLayout();
            // 
-            // EthernetBootEnabled
+            // EthernetBootFileGroup
            // 
-            this.EthernetBootEnabled.AutoSize = true;
-            this.EthernetBootEnabled.Location = new System.Drawing.Point(7, 12);
-            this.EthernetBootEnabled.Name = "EthernetBootEnabled";
-            this.EthernetBootEnabled.Size = new System.Drawing.Size(133, 17);
-            this.EthernetBootEnabled.TabIndex = 0;
-            this.EthernetBootEnabled.Text = "Ethernet Boot Enabled";
-            this.EthernetBootEnabled.UseVisualStyleBackColor = true;
-            this.EthernetBootEnabled.CheckedChanged += new System.EventHandler(this.OnCheckChanged);
-            // 
-            // BootFileGroup
-            // 
-            this.BootFileGroup.Controls.Add(this.label1);
-            this.BootFileGroup.Controls.Add(this.BootFileComboBox);
-            this.BootFileGroup.Location = new System.Drawing.Point(4, 35);
-            this.BootFileGroup.Name = "BootFileGroup";
-            this.BootFileGroup.Size = new System.Drawing.Size(397, 62);
-            this.BootFileGroup.TabIndex = 1;
-            this.BootFileGroup.TabStop = false;
-            this.BootFileGroup.Text = "Boot File";
+            this.EthernetBootFileGroup.Controls.Add(this.label1);
+            this.EthernetBootFileGroup.Controls.Add(this.BootFileComboBox);
+            this.EthernetBootFileGroup.Location = new System.Drawing.Point(4, 106);
+            this.EthernetBootFileGroup.Name = "EthernetBootFileGroup";
+            this.EthernetBootFileGroup.Size = new System.Drawing.Size(397, 62);
+            this.EthernetBootFileGroup.TabIndex = 1;
+            this.EthernetBootFileGroup.TabStop = false;
+            this.EthernetBootFileGroup.Text = "Ethernet Boot File";
            // 
            // label1
            // 
            this.label1.AutoSize = true;
-            this.label1.Location = new System.Drawing.Point(6, 16);
+            this.label1.Location = new System.Drawing.Point(3, 16);
            this.label1.Name = "label1";
-            this.label1.Size = new System.Drawing.Size(359, 13);
+            this.label1.Size = new System.Drawing.Size(356, 13);
            this.label1.TabIndex = 1;
-            this.label1.Text = "Select a standard boot file number below, or enter a custom value in octal. ";
+            this.label1.Text = "Select a standard boot file number below, or enter a custom value in octal:";
            // 
            // BootFileComboBox
            // 
@@ -81,7 +77,7 @@
            // 
            // OKButton
            // 
-            this.OKButton.Location = new System.Drawing.Point(245, 103);
+            this.OKButton.Location = new System.Drawing.Point(245, 174);
            this.OKButton.Name = "OKButton";
            this.OKButton.Size = new System.Drawing.Size(75, 23);
            this.OKButton.TabIndex = 2;
@@ -91,7 +87,7 @@
            // 
            // CancelButton
            // 
-            this.CancelButton.Location = new System.Drawing.Point(326, 103);
+            this.CancelButton.Location = new System.Drawing.Point(326, 174);
            this.CancelButton.Name = "CancelButton";
            this.CancelButton.Size = new System.Drawing.Size(75, 23);
            this.CancelButton.TabIndex = 3;
@@ -99,35 +95,105 @@
            this.CancelButton.UseVisualStyleBackColor = true;
            this.CancelButton.Click += new System.EventHandler(this.CancelButton_Click);
            // 
+            // groupBox1
+            // 
+            this.groupBox1.Controls.Add(this.EthernetBootRadioButton);
+            this.groupBox1.Controls.Add(this.DiskBootRadioButton);
+            this.groupBox1.Location = new System.Drawing.Point(4, 9);
+            this.groupBox1.Name = "groupBox1";
+            this.groupBox1.Size = new System.Drawing.Size(397, 43);
+            this.groupBox1.TabIndex = 4;
+            this.groupBox1.TabStop = false;
+            this.groupBox1.Text = "Alternate Boot Type";
+            // 
+            // EthernetBootRadioButton
+            // 
+            this.EthernetBootRadioButton.AutoSize = true;
+            this.EthernetBootRadioButton.Location = new System.Drawing.Point(86, 20);
+            this.EthernetBootRadioButton.Name = "EthernetBootRadioButton";
+            this.EthernetBootRadioButton.Size = new System.Drawing.Size(90, 17);
+            this.EthernetBootRadioButton.TabIndex = 1;
+            this.EthernetBootRadioButton.TabStop = true;
+            this.EthernetBootRadioButton.Text = "Ethernet Boot";
+            this.EthernetBootRadioButton.UseVisualStyleBackColor = true;            
+
+            // 
+            // DiskBootRadioButton
+            // 
+            this.DiskBootRadioButton.AutoSize = true;
+            this.DiskBootRadioButton.Location = new System.Drawing.Point(9, 20);
+            this.DiskBootRadioButton.Name = "DiskBootRadioButton";
+            this.DiskBootRadioButton.Size = new System.Drawing.Size(71, 17);
+            this.DiskBootRadioButton.TabIndex = 0;
+            this.DiskBootRadioButton.TabStop = true;
+            this.DiskBootRadioButton.Text = "Disk Boot";
+            this.DiskBootRadioButton.UseVisualStyleBackColor = true;
+            
+            // 
+            // DiskBootGroupBox
+            // 
+            this.DiskBootGroupBox.Controls.Add(this.DiskBootAddressTextBox);
+            this.DiskBootGroupBox.Controls.Add(this.label2);
+            this.DiskBootGroupBox.Location = new System.Drawing.Point(4, 58);
+            this.DiskBootGroupBox.Name = "DiskBootGroupBox";
+            this.DiskBootGroupBox.Size = new System.Drawing.Size(397, 42);
+            this.DiskBootGroupBox.TabIndex = 2;
+            this.DiskBootGroupBox.TabStop = false;
+            this.DiskBootGroupBox.Text = "Disk Boot Address";
+            // 
+            // DiskBootAddressTextBox
+            // 
+            this.DiskBootAddressTextBox.Location = new System.Drawing.Point(186, 13);
+            this.DiskBootAddressTextBox.Name = "DiskBootAddressTextBox";
+            this.DiskBootAddressTextBox.Size = new System.Drawing.Size(94, 20);
+            this.DiskBootAddressTextBox.TabIndex = 2;
+            // 
+            // label2
+            // 
+            this.label2.AutoSize = true;
+            this.label2.Location = new System.Drawing.Point(3, 16);
+            this.label2.Name = "label2";
+            this.label2.Size = new System.Drawing.Size(177, 13);
+            this.label2.TabIndex = 1;
+            this.label2.Text = "Enter the octal disk address to boot:";
+            // 
            // AlternateBootOptions
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
-            this.ClientSize = new System.Drawing.Size(403, 128);
+            this.ClientSize = new System.Drawing.Size(406, 201);
+            this.Controls.Add(this.DiskBootGroupBox);
+            this.Controls.Add(this.groupBox1);
            this.Controls.Add(this.CancelButton);
            this.Controls.Add(this.OKButton);
-            this.Controls.Add(this.BootFileGroup);
-            this.Controls.Add(this.EthernetBootEnabled);
+            this.Controls.Add(this.EthernetBootFileGroup);
            this.Name = "AlternateBootOptions";
            this.ShowIcon = false;
            this.ShowInTaskbar = false;
            this.SizeGripStyle = System.Windows.Forms.SizeGripStyle.Hide;
            this.StartPosition = System.Windows.Forms.FormStartPosition.CenterParent;
-            this.Text = "Ethernet Boot Options";
-            this.BootFileGroup.ResumeLayout(false);
-            this.BootFileGroup.PerformLayout();
+            this.Text = "Alternate Boot Options";
+            this.EthernetBootFileGroup.ResumeLayout(false);
+            this.EthernetBootFileGroup.PerformLayout();
+            this.groupBox1.ResumeLayout(false);
+            this.groupBox1.PerformLayout();
+            this.DiskBootGroupBox.ResumeLayout(false);
+            this.DiskBootGroupBox.PerformLayout();
            this.ResumeLayout(false);
-            this.PerformLayout();

        }

        #endregion
-
-        private System.Windows.Forms.CheckBox EthernetBootEnabled;
-        private System.Windows.Forms.GroupBox BootFileGroup;
+        private System.Windows.Forms.GroupBox EthernetBootFileGroup;
        private System.Windows.Forms.Label label1;
        private System.Windows.Forms.ComboBox BootFileComboBox;
        private System.Windows.Forms.Button OKButton;
        private System.Windows.Forms.Button CancelButton;
+        private System.Windows.Forms.GroupBox groupBox1;
+        private System.Windows.Forms.RadioButton EthernetBootRadioButton;
+        private System.Windows.Forms.RadioButton DiskBootRadioButton;
+        private System.Windows.Forms.GroupBox DiskBootGroupBox;
+        private System.Windows.Forms.Label label2;
+        private System.Windows.Forms.TextBox DiskBootAddressTextBox;
    }
 }
--- a/Contralto/UI/AlternateBootWindow.cs
+++ b/Contralto/UI/AlternateBootWindow.cs
@@ -14,16 +14,22 @@ namespace Contralto
    {
        public AlternateBootOptions()
        {
-            InitializeComponent();
-
+            InitializeComponent();            
+                        
            LoadBootEntries();

-            BootFileGroup.Enabled = EthernetBootEnabled.Checked = Configuration.EthernetBootEnabled;
-
-            SelectBootFile(Configuration.BootAddress);
-
-        }
+            if (Configuration.AlternateBootType == AlternateBootType.Disk)
+            {
+                DiskBootRadioButton.Checked = true;
+            }
+            else
+            {
+                EthernetBootRadioButton.Checked = true;
+            }

+            SetBootAddress(Configuration.BootAddress);
+            SelectBootFile(Configuration.BootFile);
+        }        

        private void LoadBootEntries()
        {
@@ -55,18 +61,33 @@ namespace Contralto
            }
        }       

+        private void SetBootAddress(ushort address)
+        {
+            DiskBootAddressTextBox.Text = Conversion.ToOctal(address);
+        }
+
        private void BootFileComboBox_SelectedIndexChanged(object sender, EventArgs e)
        {
-            _selectedBoot = ((BootFileEntry)BootFileComboBox.SelectedItem).FileNumber;
-        }
+            _selectedBootFile = ((BootFileEntry)BootFileComboBox.SelectedItem).FileNumber;
+        }        

        private void OKButton_Click(object sender, EventArgs e)
        {
+            try
+            {
+                _selectedBootAddress = Convert.ToUInt16(DiskBootAddressTextBox.Text, 8);
+            }
+            catch
+            {
+                MessageBox.Show("The disk boot address must be an octal value between 0 and 177777.");
+                return;
+            }            
+
            if (BootFileComboBox.SelectedItem == null)
            {
                try
                {
-                    _selectedBoot = Convert.ToUInt16(BootFileComboBox.Text, 8);
+                    _selectedBootFile = Convert.ToUInt16(BootFileComboBox.Text, 8);
                }
                catch
                {
@@ -76,11 +97,20 @@ namespace Contralto
            }
            else
            {
-                _selectedBoot = ((BootFileEntry)BootFileComboBox.SelectedItem).FileNumber;
+                _selectedBootFile = ((BootFileEntry)BootFileComboBox.SelectedItem).FileNumber;
            }
+            
+            Configuration.BootAddress = _selectedBootAddress;
+            Configuration.BootFile = _selectedBootFile;

-            Configuration.BootAddress = _selectedBoot;
-            Configuration.EthernetBootEnabled = _bootEnabled;
+            if (DiskBootRadioButton.Checked)
+            {            
+                Configuration.AlternateBootType = AlternateBootType.Disk;
+            }
+            else
+            {                               
+                Configuration.AlternateBootType = AlternateBootType.Ethernet;
+            }

            this.Close();
        }
@@ -88,12 +118,7 @@ namespace Contralto
        private void CancelButton_Click(object sender, EventArgs e)
        {
            this.Close();
-        }
-
-        private void OnCheckChanged(object sender, EventArgs e)
-        {
-            BootFileGroup.Enabled = _bootEnabled = EthernetBootEnabled.Checked;
-        }
+        }      

        private BootFileEntry[] _bootEntries = new BootFileEntry[]
        {
@@ -118,8 +143,8 @@ namespace Contralto

       

-        private ushort _selectedBoot;
-        private bool _bootEnabled;
+        private ushort _selectedBootFile;
+        private ushort _selectedBootAddress;

    }

--- a/Contralto/UI/AltoWindow.Designer.cs
+++ b/Contralto/UI/AltoWindow.Designer.cs
@@ -44,7 +44,7 @@
            this.loadToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();
            this.unloadToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();
            this.Drive1ImageName = new System.Windows.Forms.ToolStripMenuItem();
-            this.enableAlternateBootToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();
+            this.AlternateBootToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();
            this.SystemEthernetBootMenu = new System.Windows.Forms.ToolStripMenuItem();
            this.optionsToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();
            this.SystemShowDebuggerMenuItem = new System.Windows.Forms.ToolStripMenuItem();
@@ -88,7 +88,7 @@
            this.fileToolStripMenuItem.DropDownItems.AddRange(new System.Windows.Forms.ToolStripItem[] {
            this.exitToolStripMenuItem});
            this.fileToolStripMenuItem.Name = "fileToolStripMenuItem";
-            this.fileToolStripMenuItem.Size = new System.Drawing.Size(35, 20);
+            this.fileToolStripMenuItem.Size = new System.Drawing.Size(37, 20);
            this.fileToolStripMenuItem.Text = "File";
            // 
            // exitToolStripMenuItem
@@ -105,12 +105,12 @@
            this.SystemResetMenuItem,
            this.drive0ToolStripMenuItem,
            this.drive1ToolStripMenuItem,
-            this.enableAlternateBootToolStripMenuItem,
+            this.AlternateBootToolStripMenuItem,
            this.SystemEthernetBootMenu,
            this.optionsToolStripMenuItem,
            this.SystemShowDebuggerMenuItem});
            this.settingsToolStripMenuItem.Name = "settingsToolStripMenuItem";
-            this.settingsToolStripMenuItem.Size = new System.Drawing.Size(54, 20);
+            this.settingsToolStripMenuItem.Size = new System.Drawing.Size(57, 20);
            this.settingsToolStripMenuItem.Text = "System";
            // 
            // SystemStartMenuItem
@@ -118,7 +118,7 @@
            this.SystemStartMenuItem.Name = "SystemStartMenuItem";
            this.SystemStartMenuItem.ShortcutKeys = ((System.Windows.Forms.Keys)(((System.Windows.Forms.Keys.Control | System.Windows.Forms.Keys.Alt) 
            | System.Windows.Forms.Keys.S)));
-            this.SystemStartMenuItem.Size = new System.Drawing.Size(210, 22);
+            this.SystemStartMenuItem.Size = new System.Drawing.Size(223, 22);
            this.SystemStartMenuItem.Text = "Start";
            this.SystemStartMenuItem.Click += new System.EventHandler(this.OnSystemStartMenuClick);
            // 
@@ -128,7 +128,7 @@
            this.SystemResetMenuItem.Name = "SystemResetMenuItem";
            this.SystemResetMenuItem.ShortcutKeys = ((System.Windows.Forms.Keys)(((System.Windows.Forms.Keys.Control | System.Windows.Forms.Keys.Alt) 
            | System.Windows.Forms.Keys.R)));
-            this.SystemResetMenuItem.Size = new System.Drawing.Size(210, 22);
+            this.SystemResetMenuItem.Size = new System.Drawing.Size(223, 22);
            this.SystemResetMenuItem.Text = "Reset";
            this.SystemResetMenuItem.Click += new System.EventHandler(this.OnSystemResetMenuClick);
            // 
@@ -139,7 +139,7 @@
            this.unloadToolStripMenuItem1,
            this.Drive0ImageName});
            this.drive0ToolStripMenuItem.Name = "drive0ToolStripMenuItem";
-            this.drive0ToolStripMenuItem.Size = new System.Drawing.Size(210, 22);
+            this.drive0ToolStripMenuItem.Size = new System.Drawing.Size(223, 22);
            this.drive0ToolStripMenuItem.Text = "Drive 0";
            // 
            // loadToolStripMenuItem1
@@ -147,14 +147,14 @@
            this.loadToolStripMenuItem1.Name = "loadToolStripMenuItem1";
            this.loadToolStripMenuItem1.ShortcutKeys = ((System.Windows.Forms.Keys)(((System.Windows.Forms.Keys.Control | System.Windows.Forms.Keys.Alt) 
            | System.Windows.Forms.Keys.L)));
-            this.loadToolStripMenuItem1.Size = new System.Drawing.Size(167, 22);
+            this.loadToolStripMenuItem1.Size = new System.Drawing.Size(172, 22);
            this.loadToolStripMenuItem1.Text = "Load...";
            this.loadToolStripMenuItem1.Click += new System.EventHandler(this.OnSystemDrive0LoadClick);
            // 
            // unloadToolStripMenuItem1
            // 
            this.unloadToolStripMenuItem1.Name = "unloadToolStripMenuItem1";
-            this.unloadToolStripMenuItem1.Size = new System.Drawing.Size(167, 22);
+            this.unloadToolStripMenuItem1.Size = new System.Drawing.Size(172, 22);
            this.unloadToolStripMenuItem1.Text = "Unload...";
            this.unloadToolStripMenuItem1.Click += new System.EventHandler(this.OnSystemDrive0UnloadClick);
            // 
@@ -162,7 +162,7 @@
            // 
            this.Drive0ImageName.Enabled = false;
            this.Drive0ImageName.Name = "Drive0ImageName";
-            this.Drive0ImageName.Size = new System.Drawing.Size(167, 22);
+            this.Drive0ImageName.Size = new System.Drawing.Size(172, 22);
            this.Drive0ImageName.Text = "Image Name";
            // 
            // drive1ToolStripMenuItem
@@ -172,20 +172,20 @@
            this.unloadToolStripMenuItem,
            this.Drive1ImageName});
            this.drive1ToolStripMenuItem.Name = "drive1ToolStripMenuItem";
-            this.drive1ToolStripMenuItem.Size = new System.Drawing.Size(210, 22);
+            this.drive1ToolStripMenuItem.Size = new System.Drawing.Size(223, 22);
            this.drive1ToolStripMenuItem.Text = "Drive 1";
            // 
            // loadToolStripMenuItem
            // 
            this.loadToolStripMenuItem.Name = "loadToolStripMenuItem";
-            this.loadToolStripMenuItem.Size = new System.Drawing.Size(134, 22);
+            this.loadToolStripMenuItem.Size = new System.Drawing.Size(142, 22);
            this.loadToolStripMenuItem.Text = "Load...";
            this.loadToolStripMenuItem.Click += new System.EventHandler(this.OnSystemDrive1LoadClick);
            // 
            // unloadToolStripMenuItem
            // 
            this.unloadToolStripMenuItem.Name = "unloadToolStripMenuItem";
-            this.unloadToolStripMenuItem.Size = new System.Drawing.Size(134, 22);
+            this.unloadToolStripMenuItem.Size = new System.Drawing.Size(142, 22);
            this.unloadToolStripMenuItem.Text = "Unload...";
            this.unloadToolStripMenuItem.Click += new System.EventHandler(this.OnSystemDrive1UnloadClick);
            // 
@@ -193,27 +193,28 @@
            // 
            this.Drive1ImageName.Enabled = false;
            this.Drive1ImageName.Name = "Drive1ImageName";
-            this.Drive1ImageName.Size = new System.Drawing.Size(134, 22);
+            this.Drive1ImageName.Size = new System.Drawing.Size(142, 22);
            this.Drive1ImageName.Text = "Image Name";
            // 
-            // enableAlternateBootToolStripMenuItem
+            // AlternateBootToolStripMenuItem
            // 
-            this.enableAlternateBootToolStripMenuItem.Name = "enableAlternateBootToolStripMenuItem";
-            this.enableAlternateBootToolStripMenuItem.Size = new System.Drawing.Size(210, 22);
-            this.enableAlternateBootToolStripMenuItem.Text = "Enable Alternate Boot";
+            this.AlternateBootToolStripMenuItem.Name = "AlternateBootToolStripMenuItem";
+            this.AlternateBootToolStripMenuItem.Size = new System.Drawing.Size(223, 22);
+            this.AlternateBootToolStripMenuItem.Text = "Start with Alternate Boot";
+            this.AlternateBootToolStripMenuItem.Click += new System.EventHandler(this.OnStartWithAlternateBootClicked);
            // 
            // SystemEthernetBootMenu
            // 
            this.SystemEthernetBootMenu.Name = "SystemEthernetBootMenu";
-            this.SystemEthernetBootMenu.Size = new System.Drawing.Size(210, 22);
+            this.SystemEthernetBootMenu.Size = new System.Drawing.Size(223, 22);
            this.SystemEthernetBootMenu.Text = "Alternate Boot Options...";
            this.SystemEthernetBootMenu.Click += new System.EventHandler(this.OnAlternateBootOptionsClicked);
            // 
            // optionsToolStripMenuItem
            // 
            this.optionsToolStripMenuItem.Name = "optionsToolStripMenuItem";
-            this.optionsToolStripMenuItem.Size = new System.Drawing.Size(210, 22);
-            this.optionsToolStripMenuItem.Text = "Options...";
+            this.optionsToolStripMenuItem.Size = new System.Drawing.Size(223, 22);
+            this.optionsToolStripMenuItem.Text = "System Configuration...";
            this.optionsToolStripMenuItem.Click += new System.EventHandler(this.OnSystemOptionsClick);
            // 
            // SystemShowDebuggerMenuItem
@@ -221,7 +222,7 @@
            this.SystemShowDebuggerMenuItem.Name = "SystemShowDebuggerMenuItem";
            this.SystemShowDebuggerMenuItem.ShortcutKeys = ((System.Windows.Forms.Keys)(((System.Windows.Forms.Keys.Control | System.Windows.Forms.Keys.Alt) 
            | System.Windows.Forms.Keys.D)));
-            this.SystemShowDebuggerMenuItem.Size = new System.Drawing.Size(210, 22);
+            this.SystemShowDebuggerMenuItem.Size = new System.Drawing.Size(223, 22);
            this.SystemShowDebuggerMenuItem.Text = "Show Debugger";
            this.SystemShowDebuggerMenuItem.Click += new System.EventHandler(this.OnDebuggerShowClick);
            // 
@@ -230,13 +231,13 @@
            this.helpToolStripMenuItem.DropDownItems.AddRange(new System.Windows.Forms.ToolStripItem[] {
            this.aboutToolStripMenuItem});
            this.helpToolStripMenuItem.Name = "helpToolStripMenuItem";
-            this.helpToolStripMenuItem.Size = new System.Drawing.Size(40, 20);
+            this.helpToolStripMenuItem.Size = new System.Drawing.Size(44, 20);
            this.helpToolStripMenuItem.Text = "Help";
            // 
            // aboutToolStripMenuItem
            // 
            this.aboutToolStripMenuItem.Name = "aboutToolStripMenuItem";
-            this.aboutToolStripMenuItem.Size = new System.Drawing.Size(103, 22);
+            this.aboutToolStripMenuItem.Size = new System.Drawing.Size(107, 22);
            this.aboutToolStripMenuItem.Text = "About";
            this.aboutToolStripMenuItem.Click += new System.EventHandler(this.OnHelpAboutClick);
            // 
@@ -256,19 +257,19 @@
            // CaptureStatusLabel
            // 
            this.CaptureStatusLabel.Name = "CaptureStatusLabel";
-            this.CaptureStatusLabel.Size = new System.Drawing.Size(102, 17);
+            this.CaptureStatusLabel.Size = new System.Drawing.Size(109, 17);
            this.CaptureStatusLabel.Text = "CaptureStatusLabel";
            // 
            // SystemStatusLabel
            // 
            this.SystemStatusLabel.Name = "SystemStatusLabel";
-            this.SystemStatusLabel.Size = new System.Drawing.Size(98, 17);
+            this.SystemStatusLabel.Size = new System.Drawing.Size(105, 17);
            this.SystemStatusLabel.Text = "SystemStatusLabel";
            // 
            // DiskStatusLabel
            // 
            this.DiskStatusLabel.Name = "DiskStatusLabel";
-            this.DiskStatusLabel.Size = new System.Drawing.Size(82, 17);
+            this.DiskStatusLabel.Size = new System.Drawing.Size(89, 17);
            this.DiskStatusLabel.Text = "DiskStatusLabel";
            // 
            // AltoWindow
@@ -328,6 +329,6 @@
        private System.Windows.Forms.ToolStripStatusLabel SystemStatusLabel;
        private System.Windows.Forms.ToolStripStatusLabel DiskStatusLabel;
        private System.Windows.Forms.ToolStripMenuItem SystemEthernetBootMenu;
-        private System.Windows.Forms.ToolStripMenuItem enableAlternateBootToolStripMenuItem;
+        private System.Windows.Forms.ToolStripMenuItem AlternateBootToolStripMenuItem;
    }
 }
--- a/Contralto/UI/AltoWindow.cs
+++ b/Contralto/UI/AltoWindow.cs
@@ -47,8 +47,8 @@ namespace Contralto
            _controller.ErrorCallback += OnExecutionError;

            // Update disk image UI info
-            Drive0ImageName.Text = _system.DiskController.Drives[0].IsLoaded ? System.IO.Path.GetFileName(_system.DiskController.Drives[0].Pack.PackName) : _noImageLoadedText;
-            Drive1ImageName.Text = _system.DiskController.Drives[1].IsLoaded ? System.IO.Path.GetFileName(_system.DiskController.Drives[1].Pack.PackName) : _noImageLoadedText;
+            Drive0ImageName.Text = _system.DiskController.Drives[0].IsLoaded ? Path.GetFileName(_system.DiskController.Drives[0].Pack.PackName) : _noImageLoadedText;
+            Drive1ImageName.Text = _system.DiskController.Drives[1].IsLoaded ? Path.GetFileName(_system.DiskController.Drives[1].Pack.PackName) : _noImageLoadedText;
        }

        /// <summary>
@@ -58,21 +58,25 @@ namespace Contralto
        /// <param name="e"></param>
        private void OnSystemStartMenuClick(object sender, EventArgs e)
        {
-            // Disable "Start" menu item
-            SystemStartMenuItem.Enabled = false;
+            StartSystem(AlternateBootType.None);
+        }        

-            // Enable "Reset" menu item
-            SystemResetMenuItem.Enabled = true;
+        private void OnStartWithAlternateBootClicked(object sender, EventArgs e)
+        {
+            if (_controller.IsRunning)
+            {
+                _controller.Reset(Configuration.AlternateBootType);
+            }
+            else
+            {
+                StartSystem(Configuration.AlternateBootType);                
+            }

-            _controller.StartExecution();
-
-            SystemStatusLabel.Text = _systemRunningText;
-
-    }
+        }

        private void OnSystemResetMenuClick(object sender, EventArgs e)
        {
-            _controller.Reset();
+            _controller.Reset(AlternateBootType.None);
        }

        private void OnSystemDrive0LoadClick(object sender, EventArgs e)
@@ -90,6 +94,7 @@ namespace Contralto
                CommitDiskPack(0);
                _system.LoadDrive(0, path);
                Drive0ImageName.Text = System.IO.Path.GetFileName(path);
+                Configuration.Drive0Image = path;
            }
            catch(Exception ex)
            {
@@ -104,6 +109,7 @@ namespace Contralto
            CommitDiskPack(0);
            _system.UnloadDrive(0);
            Drive0ImageName.Text = _noImageLoadedText;
+            Configuration.Drive0Image = String.Empty;
        }

        private void OnSystemDrive1LoadClick(object sender, EventArgs e)
@@ -121,6 +127,7 @@ namespace Contralto
                CommitDiskPack(1);
                _system.LoadDrive(1, path);
                Drive1ImageName.Text = System.IO.Path.GetFileName(path);
+                Configuration.Drive1Image = path;
            }
            catch (Exception ex)
            {
@@ -135,17 +142,13 @@ namespace Contralto
            CommitDiskPack(1);
            _system.UnloadDrive(1);
            Drive1ImageName.Text = _noImageLoadedText;
+            Configuration.Drive1Image = String.Empty;
        }

        private void OnAlternateBootOptionsClicked(object sender, EventArgs e)
        {
            AlternateBootOptions bootWindow = new AlternateBootOptions();
-            bootWindow.ShowDialog();
-
-            //
-            // Apply settings to system.
-            //
-            _system.PressBootKeys();
+            bootWindow.ShowDialog();    
        }

        private void OnSystemOptionsClick(object sender, EventArgs e)
@@ -206,6 +209,9 @@ namespace Contralto
            CommitDiskPack(0);
            CommitDiskPack(1);

+            // Commit current configuration to disk
+            Configuration.WriteConfiguration();
+
            this.Dispose();
            Application.Exit();
        }
@@ -268,6 +274,19 @@ namespace Contralto
            }
        }

+        private void StartSystem(AlternateBootType bootType)
+        {
+            // Disable "Start" menu item
+            SystemStartMenuItem.Enabled = false;
+
+            // Enable "Reset" menu item
+            SystemResetMenuItem.Enabled = true;
+
+            _controller.StartExecution(bootType);
+
+            SystemStatusLabel.Text = _systemRunningText;
+        }
+
        //
        // Display handling
        //
--- a/Contralto/UI/Debugger.cs
+++ b/Contralto/UI/Debugger.cs
@@ -718,7 +718,7 @@ namespace Contralto
        {
            _execType = ExecutionType.Step;
            SetExecutionState(ExecutionState.SingleStep);
-            _controller.StartExecution();                        
+            _controller.StartExecution(AlternateBootType.None);                        
        }

        private void OnAutoStepButtonClicked(object sender, EventArgs e)
@@ -729,7 +729,7 @@ namespace Contralto
            //
            _execType = ExecutionType.Auto;
            SetExecutionState(ExecutionState.AutoStep);
-            _controller.StartExecution();
+            _controller.StartExecution(AlternateBootType.None);
        }

        private void RunButton_Click(object sender, EventArgs e)
@@ -740,14 +740,14 @@ namespace Contralto
            //                  
            _execType = ExecutionType.Normal;
            SetExecutionState(ExecutionState.Running);
-            _controller.StartExecution();         
+            _controller.StartExecution(AlternateBootType.None);         
        }

        private void RunToNextTaskButton_Click(object sender, EventArgs e)
        {            
            _execType = ExecutionType.NextTask;
            SetExecutionState(ExecutionState.Running);
-            _controller.StartExecution();
+            _controller.StartExecution(AlternateBootType.None);
        }

        /// <summary>
@@ -762,7 +762,7 @@ namespace Contralto
        {
            _execType = ExecutionType.NextNovaInstruction;
            SetExecutionState(ExecutionState.Running);
-            _controller.StartExecution();
+            _controller.StartExecution(AlternateBootType.None);
            
        }

@@ -775,7 +775,7 @@ namespace Contralto

        private void ResetButton_Click(object sender, EventArgs e)
        {
-            _controller.Reset();            
+            _controller.Reset(AlternateBootType.None);            
            Refresh();
        }    
        
--- a/Contralto/UI/SystemOptions.Designer.cs
+++ b/Contralto/UI/SystemOptions.Designer.cs
@@ -48,6 +48,7 @@
            this.InterlaceDisplayCheckBox = new System.Windows.Forms.CheckBox();
            this.OKButton = new System.Windows.Forms.Button();
            this.CancelButton = new System.Windows.Forms.Button();
+            this.NoEncapsulationRadioButton = new System.Windows.Forms.RadioButton();
            this.tabControl1.SuspendLayout();
            this.tabPage1.SuspendLayout();
            this.tabPage2.SuspendLayout();
@@ -142,6 +143,7 @@
            // 
            // groupBox1
            // 
+            this.groupBox1.Controls.Add(this.NoEncapsulationRadioButton);
            this.groupBox1.Controls.Add(this.RawEthernetRadioButton);
            this.groupBox1.Controls.Add(this.UDPRadioButton);
            this.groupBox1.Location = new System.Drawing.Point(10, 30);
@@ -154,7 +156,7 @@
            // RawEthernetRadioButton
            // 
            this.RawEthernetRadioButton.AutoSize = true;
-            this.RawEthernetRadioButton.Location = new System.Drawing.Point(77, 16);
+            this.RawEthernetRadioButton.Location = new System.Drawing.Point(63, 16);
            this.RawEthernetRadioButton.Name = "RawEthernetRadioButton";
            this.RawEthernetRadioButton.Size = new System.Drawing.Size(186, 17);
            this.RawEthernetRadioButton.TabIndex = 1;
@@ -271,6 +273,17 @@
            this.CancelButton.UseVisualStyleBackColor = true;
            this.CancelButton.Click += new System.EventHandler(this.CancelButton_Click);
            // 
+            // NoEncapsulation
+            // 
+            this.NoEncapsulationRadioButton.AutoSize = true;
+            this.NoEncapsulationRadioButton.Location = new System.Drawing.Point(255, 16);
+            this.NoEncapsulationRadioButton.Name = "NoEncapsulation";
+            this.NoEncapsulationRadioButton.Size = new System.Drawing.Size(51, 17);
+            this.NoEncapsulationRadioButton.TabIndex = 2;
+            this.NoEncapsulationRadioButton.TabStop = true;
+            this.NoEncapsulationRadioButton.Text = "None";
+            this.NoEncapsulationRadioButton.UseVisualStyleBackColor = true;
+            // 
            // SystemOptions
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
@@ -320,5 +333,6 @@
        private System.Windows.Forms.GroupBox groupBox1;
        private System.Windows.Forms.RadioButton RawEthernetRadioButton;
        private System.Windows.Forms.RadioButton UDPRadioButton;
+        private System.Windows.Forms.RadioButton NoEncapsulationRadioButton;
    }
 }
--- a/Contralto/UI/SystemOptions.cs
+++ b/Contralto/UI/SystemOptions.cs
@@ -54,55 +54,82 @@ namespace Contralto.UI
            {
                // If PCAP isn't installed, the RAW Ethernet option is not available.           
                RawEthernetRadioButton.Enabled = false;
-                UDPRadioButton.Checked = true;
-            }
-            else
-            {
-                if (Configuration.HostPacketInterfaceType == PacketInterfaceType.UDPEncapsulation)
-                {
-                    UDPRadioButton.Checked = true;
-                }
-                else
-                {
-                    RawEthernetRadioButton.Checked = true;
-                }
-            }

-            PopulateNetworkAdapterList(UDPRadioButton.Checked);                       
+                // Ensure the option isn't set in the configuration.
+                if (Configuration.HostPacketInterfaceType == PacketInterfaceType.EthernetEncapsulation)
+                {
+                    Configuration.HostPacketInterfaceType = PacketInterfaceType.None;
+                }
+            }
+            
+            switch(Configuration.HostPacketInterfaceType)
+            {
+                case PacketInterfaceType.UDPEncapsulation:
+                    UDPRadioButton.Checked = true;
+                    break;
+
+                case PacketInterfaceType.EthernetEncapsulation:
+                    RawEthernetRadioButton.Checked = true;
+                    break;
+
+                case PacketInterfaceType.None:
+                    NoEncapsulationRadioButton.Checked = true;
+                    break;
+            }                                                    
+
+            PopulateNetworkAdapterList(Configuration.HostPacketInterfaceType);                       
        }

-        private void PopulateNetworkAdapterList(bool udpEncapsulation)
+        private void PopulateNetworkAdapterList(PacketInterfaceType encapType)
        {
            //
            // Populate the list with the interfaces available on the machine, for the
            // type of encapsulation being used.
-            //            
+            //                        
+            HostInterfaceGroupBox.Enabled = encapType != PacketInterfaceType.None;
+
            EthernetInterfaceListBox.Items.Clear();

-            NetworkInterface[] interfaces = NetworkInterface.GetAllNetworkInterfaces();
-
+            
            // Add the "Use no interface" option
            EthernetInterfaceListBox.Items.Add(
                new EthernetInterface("None", "No network adapter"));

-            foreach (NetworkInterface iface in interfaces)
+            
+            switch (encapType)
            {
                // For UDP we show all interfaces that support IPV4, for Raw Ethernet we show only Ethernet interfaces.
-                if (udpEncapsulation)
-                {
-                    if (iface.Supports(NetworkInterfaceComponent.IPv4))
+                case PacketInterfaceType.UDPEncapsulation:
                    {
-                        EthernetInterfaceListBox.Items.Add(new EthernetInterface(iface.Name, iface.Description));
+                        NetworkInterface[] interfaces = NetworkInterface.GetAllNetworkInterfaces();
+
+                        foreach (NetworkInterface iface in interfaces)
+                        {
+                            if (iface.Supports(NetworkInterfaceComponent.IPv4))
+                            {
+                                EthernetInterfaceListBox.Items.Add(new EthernetInterface(iface.Name, iface.Description));
+                            }
+                        }
                    }
-                }
-                else 
-                {
-                    if (iface.NetworkInterfaceType == NetworkInterfaceType.Ethernet)
+                    break;
+
+                // Add all interfaces that PCAP knows about.
+                case PacketInterfaceType.EthernetEncapsulation:
                    {
-                        EthernetInterfaceListBox.Items.Add(new EthernetInterface(iface.Name, iface.Description));
-                    }
-                }
-            }
+                        List<EthernetInterface> ifaces = EthernetInterface.EnumerateDevices();
+
+                        foreach (EthernetInterface iface in ifaces)
+                        {
+                            EthernetInterfaceListBox.Items.Add(iface);
+                        }
+                    }                    
+                    break;
+
+                case PacketInterfaceType.None:
+                    // Add nothing.
+                    break;
+            }            
+            

            //
            // Select the one that is already selected (if any)
@@ -115,7 +142,7 @@ namespace Contralto.UI
                {
                    EthernetInterface iface = (EthernetInterface)EthernetInterfaceListBox.Items[i];

-                    if (iface.Description.ToLowerInvariant() == Configuration.HostPacketInterfaceName.ToLowerInvariant())
+                    if (iface.Description == Configuration.HostPacketInterfaceName)
                    {
                        EthernetInterfaceListBox.SelectedIndex = i;
                        break;
@@ -146,12 +173,16 @@ namespace Contralto.UI
            {
                _selectedInterfaceType = PacketInterfaceType.UDPEncapsulation;
            }
-            else
+            else if (RawEthernetRadioButton.Checked)
            {
                _selectedInterfaceType = PacketInterfaceType.EthernetEncapsulation;
            }
+            else
+            {
+                _selectedInterfaceType = PacketInterfaceType.None;
+            }

-            PopulateNetworkAdapterList(UDPRadioButton.Checked);
+            PopulateNetworkAdapterList(_selectedInterfaceType);
        }

        private void OKButton_Click(object sender, EventArgs e)
@@ -180,14 +211,14 @@ namespace Contralto.UI
            //
            // First warn the user of changes that require a restart.
            //
-            if (Configuration.HostPacketInterfaceName.ToLowerInvariant() != iface.Description.ToLowerInvariant() ||
+            if (Configuration.HostPacketInterfaceName != iface.Description ||
                Configuration.HostPacketInterfaceType != _selectedInterfaceType ||
                Configuration.SystemType != _selectedSystemType)
            {
                MessageBox.Show("Changes to CPU or Ethernet configuration will not take effect until ContrAlto is restarted.");
            }

-            //System
+            // System
            Configuration.SystemType = _selectedSystemType;

            // Ethernet
@@ -197,9 +228,7 @@ namespace Contralto.UI

            // Display
            Configuration.InterlaceDisplay = InterlaceDisplayCheckBox.Checked;
-            Configuration.ThrottleSpeed = ThrottleSpeedCheckBox.Checked;
-
-            Configuration.WriteConfiguration();
+            Configuration.ThrottleSpeed = ThrottleSpeedCheckBox.Checked;            

            this.Close();