Pipe endpoints join the connection pickers; no more COM11/COM12 auto-bind

Each device row now serves one endpoint at a time, picked from a list of
pipe:vrio / pipe:vplasma (first, default) plus the machine's COM ports —
nothing opens automatically at startup. The pipe services gained an
IsListening property and are started/stopped by the row's Open/Close
button instead of running for the whole app lifetime, which also retires
the dual-transport warning. Status line shows the active endpoint;
OFFLINE when none. Standalone vPLASMA is unchanged (hardwired COM12 +
permanent pipe). Also fixes the xUnit1031 warnings in the plasma pipe
tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -96,22 +96,54 @@ The two apps need a crossed serial link. Install a
 (e.g. `COM1 ⇄ COM11`), then:
 
 1. Run `VRio.App`, pick `COM11`, **Open**.
-2. RIOJoy will always poit to `COM1`.
+2. RIOJoy will always point to `COM1`.
 
 RIOJoy's DTR open-pulse shows up in the wire log (DSR handshake), its ~55 ms
 analog polling drives the "analog polls served" counter, and every click on
 the vRIO panel arrives at RIOJoy as real cockpit input. Two physical PCs with
 a null-modem cable work the same way.
 
+## Named pipes for DOSBox-X (no com0com)
+
+When the game runs in the patched DOSBox-X (the fork's `namedpipe` serial
+backend), the virtual ports aren't needed at all: each device's connection
+picker lists its named-pipe endpoint — `pipe:vrio`, `pipe:vplasma` —
+alongside the machine's COM ports. Select it and **Open** to serve
+`\\.\pipe\vrio` / `\\.\pipe\vplasma`; DOSBox-X connects as the client,
+retrying in the background until the pipe exists:
+
+```ini
+[serial]
+serial1 = namedpipe pipe:vrio    rxpollus:100 rxburst:16
+serial2 = namedpipe pipe:vplasma
+```
+
+A pipe is a plain byte stream, so serial data and modem lines travel as
+typed frames (`0x00 len bytes` data, `0x01 bits` DTR/RTS) — the game's DTR
+reset pulse keeps its exact position in the byte stream, and a disconnect
+reads as all-lines-low (cable unplugged). The contract lives in
+`src/VRio.Core/Device/PipeFraming.cs` on this side and `serialnamedpipe.h`
+on the fork's. TX is paced exactly like the COM path — with the 9600-baud
+wire gone, the pacer is the only thing between the host and an impossible
+burst. Each row serves one endpoint at a time — the RIO is a single-host
+device — and nothing opens automatically at startup; the COM path is
+unchanged for RIOJoy and real pods. vRIO's built-in glass and the
+standalone vPLASMA share the `vplasma` pipe name — whoever starts second
+retries until the name frees up.
+
 ## vPLASMA — the companion plasma display
 
 The cockpit's second serial device is the **plasma display**: a 128×32
 dot-matrix panel on COM2 (9600 8N1, no flow control) that the game draws
-mission text and status graphics on. `VPlasma.App` is its software replica:
-a bare-glass window that opens **COM12** (the device end of the plasma's
-null-modem pair) on startup — retrying while the port is missing or busy,
-port status in the title bar — decodes the display's command stream, and
-renders the dot matrix in plasma orange, text mode included.
+mission text and status graphics on. The software replica comes in two
+forms. **Built into vRIO**: the panel's encoder strip hosts the glass at
+top left, with its own connection row in the control strip (label colour =
+connection status; picker offers `pipe:vplasma` and the COM ports). And standalone,
+`VPlasma.App`: a bare-glass window that opens **COM12** (the device end of
+the plasma's null-modem pair) on startup — retrying while the port is
+missing or busy, port status in the title bar. Both decode the display's
+command stream and render the dot matrix in plasma orange, text mode
+included; only one can hold COM12 at a time.
 
 The command set was recovered from two Tesla 4.10 artifacts:
 `CODE\RP\MUNGA_L4\L4PLASMA.CPP` (the game's driver — it renders everything

src/VPlasma.App/MainForm.cs

@@ -7,6 +7,9 @@ namespace VPlasma.App;
 /// device end is hardwired to <see cref="PortName"/> (the plasma side of the
 /// second com0com pair) and opened automatically — a retry timer keeps
 /// trying while the port is missing or busy, and reopens it if it dies. The
+/// DOSBox-X fork's named-pipe transport (<c>\\.\pipe\vplasma</c>) is served
+/// permanently alongside it (if vRIO's built-in glass already holds the
+/// pipe name, the server just retries until it frees up). The
 /// title bar carries the port status; double-clicking the glass cycles the
 /// self-test pages (banner, charset, graphics) through the wire parser, and
 /// a right-click resets the display to its power-on state.
@@ -18,6 +21,7 @@ internal sealed class MainForm : Form
 
     private readonly VPlasmaDevice _device = new();
     private readonly VPlasmaSerialService _service;
+    private readonly VPlasmaPipeService _pipeService;
     private readonly PlasmaCanvas _canvas = new();
 
     private readonly System.Windows.Forms.Timer _reconnectTimer = new() { Interval = 3000 };
@@ -32,6 +36,7 @@ internal sealed class MainForm : Form
         StartPosition = FormStartPosition.CenterScreen;
 
         _service = new VPlasmaSerialService(_device);
+        _pipeService = new VPlasmaPipeService(_device);
 
         _canvas.Location = new Point(0, 0);
         Controls.Add(_canvas);
@@ -39,6 +44,7 @@ internal sealed class MainForm : Form
         // Device / service events arrive on the serial reader thread; marshal to the UI.
         _device.Updated += () => RunOnUi(() => _canvas.UpdateFrom(_device));
         _service.ConnectionChanged += _ => RunOnUi(UpdateTitle);
+        _pipeService.ClientChanged += _ => RunOnUi(UpdateTitle);
 
         _canvas.DoubleClick += (_, _) => RunSelfTest();
         _canvas.MouseClick += (_, e) =>
@@ -55,10 +61,12 @@ internal sealed class MainForm : Form
         {
             _reconnectTimer.Dispose();
             _service.Dispose();
+            _pipeService.Dispose();
         };
 
         _canvas.UpdateFrom(_device);
         EnsureOpen();
+        _pipeService.Start();
     }
 
     private void EnsureOpen()
@@ -82,6 +90,8 @@ internal sealed class MainForm : Form
         string status = _service.IsOpen
             ? $"{PortName} @ 9600 8N1"
             : $"{PortName} unavailable — retrying";
+        if (_pipeService.IsClientConnected)
+            status += "  •  pipe host connected";
         Text = $"vPLASMA v{Application.ProductVersion} — {status}";
     }
 

src/VPlasma.App/PlasmaCanvas.cs

@@ -11,10 +11,14 @@ namespace VPlasma.App;
 /// </summary>
 internal sealed class PlasmaCanvas : Control
 {
-    private const int DotPitch = 5;  // 4 px dot + 1 px gap → a 640×160 dot field
-    private const int DotSize = 4;
     private const int Bezel = 4;
 
+    // Dot geometry: an N px pitch renders (N−1) px dots with a 1 px gap. The
+    // standalone glass uses the default pitch 5 (4 px dots, a 640×160 dot
+    // field); vRIO embeds the same control at pitch 3 to fit its encoder strip.
+    private readonly int _dotPitch;
+    private readonly int _dotSize;
+
     private static readonly Color BezelColor = Color.FromArgb(20, 18, 16);
     private static readonly Color GlassColor = Color.FromArgb(26, 14, 6);
     private static readonly Color UnlitDot = Color.FromArgb(46, 24, 10);
@@ -30,14 +34,14 @@ internal sealed class PlasmaCanvas : Control
     private PlasmaCursorMode _cursorMode;
     private int _cellWidth = 6, _cellHeight = 8;
 
-    public PlasmaCanvas()
+    public PlasmaCanvas(int dotPitch = 5)
     {
+        _dotPitch = dotPitch;
+        _dotSize = dotPitch - 1;
         SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint |
                  ControlStyles.OptimizedDoubleBuffer | ControlStyles.FixedWidth |
                  ControlStyles.FixedHeight, true);
-        Size = new Size(
-            VPlasmaDevice.Width * DotPitch + 2 * Bezel,
-            VPlasmaDevice.Height * DotPitch + 2 * Bezel);
+        Size = SizeFor(dotPitch);
         BackColor = BezelColor;
 
         _blinkTimer.Tick += (_, _) =>
@@ -49,6 +53,11 @@ internal sealed class PlasmaCanvas : Control
         _blinkTimer.Start();
     }
 
+    /// <summary>Control size at a given dot pitch: the dot field plus bezel.</summary>
+    public static Size SizeFor(int dotPitch) => new(
+        VPlasmaDevice.Width * dotPitch + 2 * Bezel,
+        VPlasmaDevice.Height * dotPitch + 2 * Bezel);
+
     /// <summary>Snapshot the device state and repaint. Call on the UI thread.</summary>
     public void UpdateFrom(VPlasmaDevice device)
     {
@@ -77,7 +86,7 @@ internal sealed class PlasmaCanvas : Control
 
         using (var glass = new SolidBrush(GlassColor))
             g.FillRectangle(glass, Bezel - 4, Bezel - 4,
-                VPlasmaDevice.Width * DotPitch + 7, VPlasmaDevice.Height * DotPitch + 7);
+                VPlasmaDevice.Width * _dotPitch + 7, VPlasmaDevice.Height * _dotPitch + 7);
 
         using var unlit = new SolidBrush(UnlitDot);
         using var lit = new SolidBrush(LitDot);
@@ -86,7 +95,7 @@ internal sealed class PlasmaCanvas : Control
         for (int y = 0; y < VPlasmaDevice.Height; ++y)
         {
             int rowOffset = y * VPlasmaDevice.Width;
-            int py = Bezel + y * DotPitch;
+            int py = Bezel + y * _dotPitch;
             for (int x = 0; x < VPlasmaDevice.Width; ++x)
             {
                 byte dot = _frame[rowOffset + x];
@@ -96,7 +105,7 @@ internal sealed class PlasmaCanvas : Control
                 {
                     brush = (dot & VPlasmaDevice.PixelHalf) != 0 ? half : lit;
                 }
-                g.FillRectangle(brush, Bezel + x * DotPitch, py, DotSize, DotSize);
+                g.FillRectangle(brush, Bezel + x * _dotPitch, py, _dotSize, _dotSize);
             }
         }
 
@@ -108,7 +117,7 @@ internal sealed class PlasmaCanvas : Control
             int cy = _cursor.Row * _cellHeight + _cellHeight - 1;
             if (cy < VPlasmaDevice.Height)
                 for (int i = 0; i < _cellWidth && cx + i < VPlasmaDevice.Width; ++i)
-                    g.FillRectangle(lit, Bezel + (cx + i) * DotPitch, Bezel + cy * DotPitch, DotSize, DotSize);
+                    g.FillRectangle(lit, Bezel + (cx + i) * _dotPitch, Bezel + cy * _dotPitch, _dotSize, _dotSize);
         }
     }
 

src/VPlasma.Core/Device/VPlasmaPipeService.cs

@@ -0,0 +1,240 @@
+using System.IO.Pipes;
+
+namespace VPlasma.Core.Device;
+
+/// <summary>
+/// Serves a <see cref="VPlasmaDevice"/> over the named pipe that the
+/// DOSBox-X fork's <c>serial2=namedpipe pipe:vplasma</c> backend connects
+/// to — the com0com-free transport. We are the pipe <em>server</em> (the
+/// display is always present); DOSBox-X is the client and background-retries
+/// while the pipe is missing, so this service listens for the whole app
+/// lifetime alongside the COM path.
+///
+/// <para>Framing is the contract shared with the fork (see VRio.Core's
+/// <c>PipeFraming</c>, and <c>serialnamedpipe.h</c> on the fork side):
+/// <c>0x00 len bytes</c> carries serial data, <c>0x01 bits</c> carries the
+/// sender's DTR/RTS. Like the serial twin, the plasma is a pure listener —
+/// we send one lines frame on connect (DTR+RTS high, "display present") and
+/// then only ever read. The game may toggle its own lines around writes
+/// (DOS console redirection flips RTS per byte); the display doesn't care,
+/// so inbound lines frames are consumed silently.</para>
+/// </summary>
+public sealed class VPlasmaPipeService : IDisposable
+{
+    /// <summary>The contract pipe name: DOSBox-X connects to <c>\\.\pipe\vplasma</c>.</summary>
+    public const string DefaultPipeName = "vplasma";
+
+    // Frame types and line bits, per the shared contract.
+    private const byte DataType = 0x00;
+    private const byte LinesType = 0x01;
+    private const byte LinesPresent = 0x03; // DTR + RTS
+
+    private readonly VPlasmaDevice _device;
+    private readonly string _pipeName;
+
+    private NamedPipeServerStream? _pipe;
+    private Thread? _server;
+    private volatile bool _running;
+    private volatile bool _clientConnected;
+
+    public VPlasmaPipeService(VPlasmaDevice device, string pipeName = DefaultPipeName)
+    {
+        _device = device ?? throw new ArgumentNullException(nameof(device));
+        if (string.IsNullOrWhiteSpace(pipeName))
+            throw new ArgumentException("Pipe name is required.", nameof(pipeName));
+        _pipeName = pipeName;
+    }
+
+    /// <summary>The served pipe name (without the <c>\\.\pipe\</c> prefix).</summary>
+    public string PipeName => _pipeName;
+
+    /// <summary>True while the server is up (whether or not a client is connected).</summary>
+    public bool IsListening => _running;
+
+    /// <summary>True while a client is connected.</summary>
+    public bool IsClientConnected => _clientConnected;
+
+    /// <summary>A client connected (true) or went away (false).</summary>
+    public event Action<bool>? ClientChanged;
+
+    /// <summary>Pipe-level log lines (listen/connect/errors).</summary>
+    public event Action<string>? Logged;
+
+    /// <summary>Start listening (idempotent). Clients may come and go forever.</summary>
+    public void Start()
+    {
+        if (_running)
+            return;
+
+        _running = true;
+        _server = new Thread(ServerLoop) { IsBackground = true, Name = $"vPLASMA pipe server ({_pipeName})" };
+        _server.Start();
+
+        Logged?.Invoke($@"Listening on \\.\pipe\{_pipeName} — DOSBox-X connects when it boots");
+    }
+
+    /// <summary>Stop listening and drop any client (idempotent).</summary>
+    public void Stop()
+    {
+        if (!_running)
+            return;
+
+        _running = false;
+        NamedPipeServerStream? pipe = _pipe;
+        _pipe = null;
+        try { pipe?.Dispose(); }
+        catch (IOException) { }
+
+        // A WaitForConnection pending on the disposed stream can survive the
+        // Dispose on net48; a throwaway client connect releases it either way.
+        try
+        {
+            using var poke = new NamedPipeClientStream(".", _pipeName, PipeDirection.Out);
+            poke.Connect(100);
+        }
+        catch (Exception ex) when (ex is IOException or TimeoutException or UnauthorizedAccessException) { }
+
+        _server?.Join(1000);
+        _server = null;
+        _clientConnected = false;
+
+        Logged?.Invoke("Pipe server stopped");
+    }
+
+    private void ServerLoop()
+    {
+        bool busyLogged = false; // log the name collision once, not per retry
+
+        while (_running)
+        {
+            NamedPipeServerStream pipe;
+            try
+            {
+                pipe = new NamedPipeServerStream(_pipeName, PipeDirection.InOut, 1,
+                    PipeTransmissionMode.Byte, PipeOptions.Asynchronous);
+            }
+            catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
+            {
+                // Name already served — e.g. vRIO's built-in glass and the
+                // standalone vPLASMA both running. Whoever loses just waits.
+                if (!busyLogged)
+                {
+                    busyLogged = true;
+                    Logged?.Invoke($@"\\.\pipe\{_pipeName} is busy ({ex.Message.TrimEnd('.')}) — retrying until it frees up");
+                }
+                for (int i = 0; i < 20 && _running; i++)
+                    Thread.Sleep(100);
+                continue;
+            }
+            busyLogged = false;
+
+            _pipe = pipe;
+            try
+            {
+                pipe.WaitForConnection();
+
+                if (_running)
+                {
+                    // Our lines frame goes first: display present.
+                    pipe.Write(new byte[] { LinesType, LinesPresent }, 0, 2);
+                    pipe.Flush();
+
+                    _clientConnected = true;
+                    Logged?.Invoke("Pipe client connected — sent lines DTR+RTS (display present)");
+                    ClientChanged?.Invoke(true);
+
+                    ReadUntilDisconnect(pipe);
+                }
+            }
+            catch (Exception ex) when (ex is IOException or ObjectDisposedException or InvalidOperationException)
+            {
+                // Disposed by Stop(), or a client vanished mid-connect.
+            }
+
+            bool wasConnected = _clientConnected;
+            _clientConnected = false;
+            _pipe = null;
+            try { pipe.Dispose(); }
+            catch (IOException) { }
+
+            if (wasConnected && _running)
+            {
+                Logged?.Invoke("Pipe client disconnected");
+                ClientChanged?.Invoke(false);
+            }
+        }
+    }
+
+    private void ReadUntilDisconnect(NamedPipeServerStream pipe)
+    {
+        // Inline deframer (the listener-only subset of VRio.Core's
+        // PipeFrameDecoder): data payloads go to the device, lines frames are
+        // consumed silently, anything else is a protocol bug — log and drop
+        // the connection rather than resync.
+        const int StateType = 0, StateLength = 1, StatePayload = 2, StateLines = 3;
+        int state = StateType, remaining = 0;
+
+        var buffer = new byte[512];
+        var payload = new byte[byte.MaxValue];
+        int fill = 0;
+
+        while (_running)
+        {
+            int n;
+            try
+            {
+                n = pipe.Read(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex) when (ex is IOException or ObjectDisposedException or InvalidOperationException or OperationCanceledException)
+            {
+                if (_running)
+                    Logged?.Invoke($"Pipe error: {ex.Message}");
+                return;
+            }
+
+            if (n == 0)
+                return; // client closed its end
+
+            for (int i = 0; i < n; i++)
+            {
+                byte b = buffer[i];
+                switch (state)
+                {
+                    case StateType when b == DataType:
+                        state = StateLength;
+                        break;
+                    case StateType when b == LinesType:
+                        state = StateLines;
+                        break;
+                    case StateType:
+                        Logged?.Invoke($"Pipe protocol violation: unknown frame type 0x{b:X2} — dropping the connection");
+                        return;
+
+                    case StateLength when b == 0:
+                        Logged?.Invoke("Pipe protocol violation: zero-length data frame — dropping the connection");
+                        return;
+                    case StateLength:
+                        remaining = b;
+                        fill = 0;
+                        state = StatePayload;
+                        break;
+
+                    case StatePayload:
+                        payload[fill++] = b;
+                        if (fill == remaining)
+                        {
+                            state = StateType;
+                            _device.OnReceived(payload, remaining);
+                        }
+                        break;
+
+                    case StateLines:
+                        state = StateType; // the display ignores host line state
+                        break;
+                }
+            }
+        }
+    }
+
+    public void Dispose() => Stop();
+}

src/VPlasma.Core/VPlasma.Core.csproj

@@ -12,7 +12,6 @@
 
   <ItemGroup>
     <PackageReference Include="System.Memory" Version="4.5.5" />
-    <PackageReference Include="Microsoft.Bcl.HashCode" Version="1.1.1" />
     <PackageReference Include="PolySharp" Version="1.14.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>

src/VRio.App/MainForm.cs

@@ -1,5 +1,7 @@
 using System.Diagnostics;
 using System.IO.Ports;
+using VPlasma.App;
+using VPlasma.Core.Device;
 using VRio.Core.Device;
 using VRio.Core.Input;
 
@@ -8,24 +10,43 @@ namespace VRio.App;
 /// <summary>
 /// vRIO main window: the interactive cockpit panel on the left (the same
 /// functional map RIOJoy's profile editor shows) and a control strip on the
-/// right — COM port, device settings, and a live wire log. At startup the
-/// usual port (<see cref="PreferredPort"/>) is opened automatically when it's
-/// available; otherwise open a COM port by hand. Point RIOJoy at the other
-/// end of the null-modem pair, and every click here arrives at RIOJoy exactly
-/// as if the physical cockpit sent it.
+/// right — connection rows, device settings, and a live wire log. The
+/// panel's encoder strip also hosts the built-in plasma glass (the vPLASMA
+/// display emulator) on its own connection row. Each row's picker offers
+/// the device's named-pipe endpoint (the DOSBox-X fork's namedpipe backend
+/// — the com0com-free path) alongside the machine's COM ports; nothing
+/// opens automatically — pick an endpoint and Open. Point RIOJoy at the
+/// other end of a null-modem pair and every click here arrives exactly as
+/// if the physical cockpit sent it; point the game at
+/// <see cref="RioPipeEndpoint"/>/<see cref="PlasmaPipeEndpoint"/> (or the
+/// COM2 passthrough at the plasma pair) and the glass lights up.
 /// </summary>
 internal sealed class MainForm : Form
 {
     /// <summary>
-    /// vRIO's usual port: the device end of the COM1⇄COM11 com0com pair.
-    /// Auto-opened at startup when present and free; the picker still allows
-    /// any other port.
+    /// The RIO's pipe endpoint as listed in the picker. Matches the
+    /// DOSBox-X conf syntax: <c>serial1=namedpipe pipe:vrio</c>.
     /// </summary>
-    private const string PreferredPort = "COM11";
+    private static readonly string RioPipeEndpoint = $"pipe:{VRioPipeService.DefaultPipeName}";
+
+    /// <summary>
+    /// The plasma's pipe endpoint as listed in the picker
+    /// (<c>serial2=namedpipe pipe:vplasma</c>).
+    /// </summary>
+    private static readonly string PlasmaPipeEndpoint = $"pipe:{VPlasmaPipeService.DefaultPipeName}";
 
     private readonly VRioDevice _device = new();
     private readonly VRioSerialService _service;
+    private readonly VRioPipeService _pipeService;
+    private readonly VPlasmaDevice _plasmaDevice = new();
+    private readonly VPlasmaSerialService _plasmaService;
+    private readonly VPlasmaPipeService _plasmaPipeService;
     private readonly PanelCanvas _canvas = new();
+    private readonly PlasmaCanvas _plasmaCanvas = new(PanelCanvas.PlasmaDotPitch)
+    {
+        Location = PanelCanvas.PlasmaSlot,
+    };
+    private int _selfTestPage;
     private readonly InputRouter _router;
     private readonly XInputGamepad _gamepad = new();
     private readonly KeyboardLampMirror _lampMirror;
@@ -34,6 +55,16 @@ internal sealed class MainForm : Form
     private readonly string _bindingsPath = Path.Combine(
         Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "vRIO", "bindings.txt");
 
+    // Port rows: one line per built-in device — a name label whose colour is
+    // the port status (green = open, gray = closed), the port picker, and an
+    // Open/Close button. The one Rescan button refreshes both pickers.
+    private readonly Label _rioLabel = new()
+    {
+        Text = "vRIO",
+        Location = new Point(12, 15),
+        AutoSize = true,
+        ForeColor = Color.Gray,
+    };
     private readonly ComboBox _portBox = new()
     {
         Location = new Point(80, 12),
@@ -42,13 +73,20 @@ internal sealed class MainForm : Form
     };
     private readonly Button _rescan = new() { Text = "Rescan", Location = new Point(214, 11), Width = 52 };
     private readonly Button _openClose = new() { Text = "Open", Location = new Point(272, 11), Width = 46 };
-    private readonly Label _linkStatus = new()
+    private readonly Label _plasmaLabel = new()
     {
-        Text = "Port closed.",
-        Location = new Point(12, 42),
+        Text = "vPLASMA",
+        Location = new Point(12, 45),
         AutoSize = true,
         ForeColor = Color.Gray,
     };
+    private readonly ComboBox _plasmaPortBox = new()
+    {
+        Location = new Point(80, 42),
+        Width = 128,
+        DropDownStyle = ComboBoxStyle.DropDownList,
+    };
+    private readonly Button _plasmaOpenClose = new() { Text = "Open", Location = new Point(272, 41), Width = 46 };
 
     private readonly CheckBox _spring = new() { Text = "Stick springs back to center", Location = new Point(10, 24), AutoSize = true, Checked = true };
     private readonly Button _centerAxes = new() { Text = "Center all axes", Location = new Point(10, 52), Width = 140, Height = 26 };
@@ -112,7 +150,8 @@ internal sealed class MainForm : Form
         AutoSize = true,
         ForeColor = Color.Gray,
         Text = "Left-click a cell: momentary press.  Right-click: latch it down.  " +
-               "Drag the X/Y box and the Z / L / R gauges to move the axes.",
+               "Drag the X/Y box and the Z / L / R gauges to move the axes.  " +
+               "Double-click the plasma glass to cycle its self-test pages; right-click it to reset.",
     };
 
     private readonly TextBox _logBox = new()
@@ -153,11 +192,18 @@ internal sealed class MainForm : Form
         KeyPreview = true; // form-level key routing for the input bindings
 
         _service = new VRioSerialService(_device);
+        _plasmaService = new VPlasmaSerialService(_plasmaDevice);
+        // The named-pipe endpoints for DOSBox-X's namedpipe serial backend,
+        // offered in the connection pickers alongside the COM ports.
+        _pipeService = new VRioPipeService(_device);
+        _plasmaPipeService = new VPlasmaPipeService(_plasmaDevice);
         _router = new InputRouter(_device);
         _lampMirror = new KeyboardLampMirror(_device);
 
-        // Panel canvas, scrolled if the window is smaller than the grid.
+        // Panel canvas, scrolled if the window is smaller than the grid. The
+        // plasma glass rides along as a child in the encoder strip's left slot.
         var scroller = new Panel { Dock = DockStyle.Fill, AutoScroll = true, BackColor = Color.FromArgb(28, 28, 28) };
+        _canvas.Controls.Add(_plasmaCanvas);
         scroller.Controls.Add(_canvas);
 
         Controls.Add(scroller);
@@ -182,12 +228,30 @@ internal sealed class MainForm : Form
         _device.Logged += line => RunOnUi(() => PrependLog(line));
         _service.Logged += line => RunOnUi(() => PrependLog(line));
         _lampMirror.Logged += line => RunOnUi(() => PrependLog(line));
-        _service.ConnectionChanged += open => RunOnUi(() => OnConnectionChanged(open));
+        _service.ConnectionChanged += _ => RunOnUi(UpdateRioEndpointUi);
         _service.HostHandshake += high => RunOnUi(() =>
             PrependLog(high ? "Host raised DTR (board-reset handshake)" : "Host dropped DTR"));
+        _pipeService.Logged += line => RunOnUi(() => PrependLog($"pipe: {line}"));
+        _pipeService.HostHandshake += high => RunOnUi(() =>
+            PrependLog(high ? "Pipe host raised DTR (board-reset handshake)" : "Pipe host dropped DTR"));
+        _plasmaPipeService.Logged += line => RunOnUi(() => PrependLog($"vPLASMA pipe: {line}"));
+
+        // Built-in plasma glass: a pure listener on its own port, same gestures
+        // as the standalone vPLASMA — double-click cycles the self-test pages,
+        // right-click resets the display to its power-on state.
+        _plasmaDevice.Updated += () => RunOnUi(() => _plasmaCanvas.UpdateFrom(_plasmaDevice));
+        _plasmaService.Logged += line => RunOnUi(() => PrependLog($"vPLASMA: {line}"));
+        _plasmaService.ConnectionChanged += _ => RunOnUi(UpdatePlasmaEndpointUi);
+        _plasmaCanvas.DoubleClick += (_, _) => RunPlasmaSelfTest();
+        _plasmaCanvas.MouseClick += (_, e) =>
+        {
+            if (e.Button == MouseButtons.Right)
+                _plasmaDevice.Reset();
+        };
 
         _rescan.Click += (_, _) => RefreshPorts();
         _openClose.Click += (_, _) => ToggleOpen();
+        _plasmaOpenClose.Click += (_, _) => TogglePlasmaOpen();
         _spring.CheckedChanged += (_, _) => _canvas.StickSpringsBack = _spring.Checked;
         _centerAxes.Click += (_, _) =>
         {
@@ -251,13 +315,17 @@ internal sealed class MainForm : Form
             _lampMirror.Dispose();
             _rawKeyboard.Dispose();
             _service.Dispose();
+            _plasmaService.Dispose();
+            _pipeService.Dispose();
+            _plasmaPipeService.Dispose();
         };
 
         RefreshPorts();
         UpdateStatus();
-        PrependLog("vRIO ready. Open a COM port, then point RIOJoy at the other end of the pair.");
+        PrependLog($"vRIO ready. Pick an endpoint per device — {RioPipeEndpoint} / {PlasmaPipeEndpoint} " +
+                   "for DOSBox-X, or a COM port for RIOJoy — and Open.");
         LoadBindings();
-        AutoOpenPreferredPort();
+        _plasmaCanvas.UpdateFrom(_plasmaDevice); // paint the power-on frame
     }
 
     private Panel BuildControlStrip()
@@ -275,11 +343,13 @@ internal sealed class MainForm : Form
             BorderStyle = BorderStyle.FixedSingle,
         };
 
-        panel.Controls.Add(new Label { Text = "COM port:", Location = new Point(12, 15), AutoSize = true });
+        panel.Controls.Add(_rioLabel);
         panel.Controls.Add(_portBox);
         panel.Controls.Add(_rescan);
         panel.Controls.Add(_openClose);
-        panel.Controls.Add(_linkStatus);
+        panel.Controls.Add(_plasmaLabel);
+        panel.Controls.Add(_plasmaPortBox);
+        panel.Controls.Add(_plasmaOpenClose);
 
         var device = new GroupBox { Text = "Device", Location = new Point(12, 68), Size = new Size(306, 88) };
         device.Controls.AddRange(new Control[] { _spring, _centerAxes, _lampsOff });
@@ -302,82 +372,132 @@ internal sealed class MainForm : Form
         return panel;
     }
 
-    // ---- Port handling -----------------------------------------------------
+    // ---- Endpoint handling ---------------------------------------------------
+    // Each device row serves one endpoint at a time — the RIO is a
+    // single-host device, so its pipe server and COM port never run together.
+
+    private bool RioOpen => _service.IsOpen || _pipeService.IsListening;
+    private bool PlasmaOpen => _plasmaService.IsOpen || _plasmaPipeService.IsListening;
 
     private void RefreshPorts()
     {
-        string? current = _portBox.SelectedItem?.ToString();
-        _portBox.Items.Clear();
-        foreach (string name in SerialPort.GetPortNames().Distinct().OrderBy(n => n, StringComparer.OrdinalIgnoreCase))
-            _portBox.Items.Add(name);
-
-        if (_portBox.Items.Count == 0)
-            return;
-        int idx = current is null ? -1 : _portBox.Items.IndexOf(current);
-        _portBox.SelectedIndex = idx >= 0 ? idx : 0;
+        string[] names = SerialPort.GetPortNames().Distinct()
+            .OrderBy(n => n, StringComparer.OrdinalIgnoreCase).ToArray();
+        // An open row's picker is disabled and shows the served endpoint;
+        // leave it alone so the display can't drift from reality.
+        if (!RioOpen)
+            RefreshPicker(_portBox, RioPipeEndpoint, names);
+        if (!PlasmaOpen)
+            RefreshPicker(_plasmaPortBox, PlasmaPipeEndpoint, names);
     }
 
-    /// <summary>
-    /// Startup convenience: if <see cref="PreferredPort"/> exists, select it
-    /// and try to open it. Failures (port missing, or busy because another
-    /// vRIO/app holds it) just log — no modal box at launch — and leave the
-    /// manual picker in charge.
-    /// </summary>
-    private void AutoOpenPreferredPort()
+    private static void RefreshPicker(ComboBox box, string pipeEndpoint, string[] portNames)
     {
-        int idx = _portBox.Items.IndexOf(PreferredPort);
-        if (idx < 0)
-        {
-            PrependLog($"{PreferredPort} not present — pick a port and open it manually.");
-            return;
-        }
+        string? current = box.SelectedItem?.ToString();
+        box.Items.Clear();
+        box.Items.Add(pipeEndpoint); // always present — a pipe server needs no hardware
+        foreach (string name in portNames)
+            box.Items.Add(name);
 
-        _portBox.SelectedIndex = idx;
-        try
-        {
-            _service.Open(PreferredPort);
-        }
-        catch (Exception ex) when (ex is IOException or UnauthorizedAccessException or InvalidOperationException or ArgumentException)
-        {
-            PrependLog($"{PreferredPort} is present but could not be opened ({ex.Message.TrimEnd('.')}) — open it manually once it frees up.");
-        }
+        int idx = current is null ? -1 : box.Items.IndexOf(current);
+        box.SelectedIndex = idx >= 0 ? idx : 0;
     }
 
     private void ToggleOpen()
     {
-        if (_service.IsOpen)
+        if (RioOpen)
         {
-            _service.Close();
-            return;
+            _service.Close();  // idempotent —
+            _pipeService.Stop(); // whichever was serving closes
+            UpdateRioEndpointUi();
         }
-
-        if (_portBox.SelectedItem?.ToString() is not { } port)
+        else
         {
-            MessageBox.Show(this, "No COM port selected. On a single PC, install a com0com virtual " +
-                "null-modem pair and open one end here.", "vRIO", MessageBoxButtons.OK, MessageBoxIcon.Information);
+            OpenFromPicker(_portBox, OpenRioEndpoint);
+        }
+    }
+
+    private void TogglePlasmaOpen()
+    {
+        if (PlasmaOpen)
+        {
+            _plasmaService.Close();
+            _plasmaPipeService.Stop();
+            UpdatePlasmaEndpointUi();
+        }
+        else
+        {
+            OpenFromPicker(_plasmaPortBox, OpenPlasmaEndpoint);
+        }
+    }
+
+    private void OpenRioEndpoint(string endpoint)
+    {
+        if (endpoint == RioPipeEndpoint)
+            _pipeService.Start();
+        else
+            _service.Open(endpoint);
+        UpdateRioEndpointUi();
+    }
+
+    private void OpenPlasmaEndpoint(string endpoint)
+    {
+        if (endpoint == PlasmaPipeEndpoint)
+            _plasmaPipeService.Start();
+        else
+            _plasmaService.Open(endpoint);
+        UpdatePlasmaEndpointUi();
+    }
+
+    private void OpenFromPicker(ComboBox box, Action<string> open)
+    {
+        if (box.SelectedItem?.ToString() is not { } endpoint)
+        {
+            MessageBox.Show(this, "No endpoint selected. Pick the device's named pipe (for " +
+                "DOSBox-X's namedpipe backend) or a COM port (for RIOJoy through a com0com " +
+                "null-modem pair).", "vRIO", MessageBoxButtons.OK, MessageBoxIcon.Information);
             return;
         }
 
         try
         {
-            _service.Open(port);
+            open(endpoint);
         }
         catch (Exception ex)
         {
-            MessageBox.Show(this, $"Could not open {port}:\n{ex.Message}", "vRIO",
+            MessageBox.Show(this, $"Could not open {endpoint}:\n{ex.Message}", "vRIO",
                 MessageBoxButtons.OK, MessageBoxIcon.Warning);
         }
     }
 
-    private void OnConnectionChanged(bool open)
+    private void UpdateRioEndpointUi()
     {
+        bool open = RioOpen;
         _openClose.Text = open ? "Close" : "Open";
-        _portBox.Enabled = _rescan.Enabled = !open;
-        _linkStatus.Text = open ? $"Serving {_service.PortName} @ 9600 8N1." : "Port closed.";
-        _linkStatus.ForeColor = open ? Color.ForestGreen : Color.Gray;
+        _portBox.Enabled = !open;
+        _rioLabel.ForeColor = open ? Color.ForestGreen : Color.Gray;
         UpdateStatus();
     }
 
+    private void UpdatePlasmaEndpointUi()
+    {
+        bool open = PlasmaOpen;
+        _plasmaOpenClose.Text = open ? "Close" : "Open";
+        _plasmaPortBox.Enabled = !open;
+        _plasmaLabel.ForeColor = open ? Color.ForestGreen : Color.Gray;
+    }
+
+    /// <summary>
+    /// Feed the next canned self-test page through the plasma's wire parser —
+    /// the same end-to-end exercise the standalone vPLASMA runs on double-click.
+    /// </summary>
+    private void RunPlasmaSelfTest()
+    {
+        byte[] bytes = PlasmaSelfTest.BuildPage(_selfTestPage);
+        _plasmaDevice.OnReceived(bytes, bytes.Length);
+        _selfTestPage = (_selfTestPage + 1) % PlasmaSelfTest.PageCount;
+    }
+
     // ---- Keyboard / gamepad input -------------------------------------------
 
     /// <summary>
@@ -588,12 +708,15 @@ internal sealed class MainForm : Form
                          $"Analog polls dropped: {dropped}\n" +
                          $"Bad checksums:        {bad}";
 
-        _canvas.StatusText = _service.IsOpen
-            ? $"vRIO {_device.VersionMajor}.{_device.VersionMinor} on {_service.PortName}\n" +
+        string? endpoint = _service.IsOpen ? _service.PortName
+            : _pipeService.IsListening ? RioPipeEndpoint
+            : null;
+        _canvas.StatusText = endpoint is not null
+            ? $"vRIO {_device.VersionMajor}.{_device.VersionMinor} on {endpoint}\n" +
               (wedged
                   ? "** ANALOG WEDGED (v4.2 bug) — awaiting host reset **"
                   : $"{polls} analog polls" + (polls > 0 ? "  (host is alive)" : "  (no host traffic yet)"))
-            : "PORT CLOSED\nOpen a COM port to go live.";
+            : "OFFLINE\nOpen an endpoint (named pipe or COM port) to go live.";
     }
 
     private void PrependLog(string line)

src/VRio.App/PanelCanvas.cs

@@ -1,3 +1,4 @@
+using VPlasma.App;
 using VRio.Core.Device;
 using VRio.Core.Panel;
 using VRio.Core.Protocol;
@@ -16,6 +17,10 @@ namespace VRio.App;
 /// fill toward full travel (negative on the wire for the throttle, positive
 /// for the pedals), and the stick covers ±80 around its center.
 ///
+/// <para>The strip's left slot hosts the built-in plasma glass: MainForm parks
+/// its <see cref="PlasmaCanvas"/> child at <see cref="PlasmaSlot"/>, and the
+/// strip height and gauge positions derive from the glass size.</para>
+///
 /// <para>Left-click = momentary press (release on mouse-up). Right-click =
 /// latch the button down / release it (handy for testing holds).</para>
 /// </summary>
@@ -24,16 +29,27 @@ internal sealed class PanelCanvas : Control
     // Cell geometry — identical to RIOJoy's PanelView so the two panels align.
     private const int CellW = 66;
     private const int CellH = 34;
-    private const int TopStrip = 78; // encoder strip: gauges end at 74, small gap to the grid
 
     private static readonly IReadOnlyList<PanelButton> AllButtons = CockpitLayout.Buttons();
 
-    // Encoder-strip geometry (same placement as RIOJoy's PanelView): Z gauge,
-    // the pedal gauges L / R, and the X/Y stick box.
+    // First grid row any group occupies (the shared layout leaves row 0
+    // empty). Rendering shifts all rows up by this, so the button grid starts
+    // right under the encoder strip instead of a blank cell row below it.
+    private static readonly int FirstRow = CockpitLayout.Groups.Min(g => g.OriginRow);
+
+    // Encoder-strip geometry. The built-in plasma glass parks at the strip's
+    // left edge (MainForm adds its PlasmaCanvas as a child at PlasmaSlot),
+    // the axis gauges — Z, the pedal gauges L / R, and the X/Y stick box —
+    // hug the grid's right edge, and the green status text fills the gap
+    // between them. The strip is exactly as tall as the glass.
+    internal const int PlasmaDotPitch = 3; // 2 px dots: the 128×32 glass fits the strip
+    internal static readonly Size PlasmaSize = PlasmaCanvas.SizeFor(PlasmaDotPitch);
     private const int StripTop = 6;
-    private const int StripH = 68;
+    internal static readonly Point PlasmaSlot = new(6, StripTop);
+    private static readonly int StripH = PlasmaSize.Height;
+    private static readonly int TopStrip = StripTop + StripH + 6; // button grid starts under the strip
     private const int Bar = 30;
-    private static readonly int BaseX = 6 * CellW - 100;
+    private static readonly int BaseX = GridWidth() - 6 - 200; // the gauge cluster spans 200 px, right-aligned
     private static readonly Rectangle BoxZ = new(BaseX, StripTop, Bar, StripH);
     private static readonly Rectangle BoxL = new(BaseX + 34, StripTop, Bar, StripH);
     private static readonly Rectangle BoxR = new(BaseX + 34 + 82 - Bar, StripTop, Bar, StripH);
@@ -109,19 +125,27 @@ internal sealed class PanelCanvas : Control
         base.Dispose(disposing);
     }
 
+    // Split from GridSize so the static gauge layout can use the width
+    // without touching TopStrip (which initializes after AllButtons).
+    private static int GridWidth()
+    {
+        int maxCol = 0;
+        foreach (PanelButton b in AllButtons)
+            if (b.Col > maxCol) maxCol = b.Col;
+        return (maxCol + 1) * CellW + 6;
+    }
+
     private static Size GridSize()
     {
-        int maxCol = 0, maxRow = 0;
+        int maxRow = 0;
         foreach (PanelButton b in AllButtons)
-        {
-            if (b.Col > maxCol) maxCol = b.Col;
             if (b.Row > maxRow) maxRow = b.Row;
-        }
-        return new Size((maxCol + 1) * CellW + 6, TopStrip + (maxRow + 2) * CellH);
+        // The last used row plus a small margin under the lowest group frame.
+        return new Size(GridWidth(), TopStrip + (maxRow - FirstRow + 1) * CellH + 6);
     }
 
     private static Rectangle Cell(int col, int row) =>
-        new(col * CellW + 2, TopStrip + row * CellH + 2, CellW - 4, CellH - 4);
+        new(col * CellW + 2, TopStrip + (row - FirstRow) * CellH + 2, CellW - 4, CellH - 4);
 
     // ---- Painting ----------------------------------------------------------
 
@@ -142,7 +166,7 @@ internal sealed class PanelCanvas : Control
         {
             var frame = new Rectangle(
                 grp.OriginCol * CellW + 1,
-                TopStrip + grp.OriginRow * CellH + 1,
+                TopStrip + (grp.OriginRow - FirstRow) * CellH + 1,
                 grp.Cols * CellW,
                 (grp.Rows + 1) * CellH);
             g.DrawRectangle(groupPen, frame);
@@ -288,10 +312,12 @@ internal sealed class PanelCanvas : Control
             new Rectangle(BoxXY.X, BoxXY.Bottom - 16, BoxXY.Width, 14), Color.Gainsboro,
             TextFormatFlags.HorizontalCenter | TextFormatFlags.Bottom);
 
-        // The mockup's green status/instruction area, right of the gauges; the
-        // live axis readout sits directly under the status lines (painted per
-        // frame, so drags track).
-        var statusRect = new Rectangle(BoxXY.Right + 16, StripTop, Width - BoxXY.Right - 24, TopStrip - StripTop - 6);
+        // The mockup's green status/instruction area, between the plasma glass
+        // and the gauges; the live axis readout sits directly under the status
+        // lines (painted per frame, so drags track).
+        var statusRect = new Rectangle(
+            PlasmaSlot.X + PlasmaSize.Width + 12, StripTop,
+            BoxZ.Left - PlasmaSlot.X - PlasmaSize.Width - 24, StripH);
         if (statusRect.Width > 60)
         {
             using var statusFont = new Font("Consolas", 8f);
@@ -307,11 +333,11 @@ internal sealed class PanelCanvas : Control
 
             short WireAxis(RioAxis a) => WireAxisProvider?.Invoke(a) ?? Axis(a);
             string readout =
-                $"Z {WireAxis(RioAxis.Throttle),4}  L {WireAxis(RioAxis.LeftPedal),3}  R {WireAxis(RioAxis.RightPedal),3}  " +
+                $"Z {WireAxis(RioAxis.Throttle),4}  L {WireAxis(RioAxis.LeftPedal),3}  R {WireAxis(RioAxis.RightPedal),3}\n" +
                 $"X {WireAxis(RioAxis.JoystickX),3}  Y {WireAxis(RioAxis.JoystickY),3}";
             TextRenderer.DrawText(g, readout, statusFont,
                 new Rectangle(statusRect.X, readoutTop, statusRect.Width, statusRect.Bottom - readoutTop), green,
-                TextFormatFlags.Left | TextFormatFlags.Top | TextFormatFlags.SingleLine);
+                TextFormatFlags.Left | TextFormatFlags.Top);
         }
     }
 

src/VRio.App/VRio.App.csproj

@@ -17,6 +17,11 @@
 
   <ItemGroup>
     <ProjectReference Include="..\VRio.Core\VRio.Core.csproj" />
+    <!-- The built-in plasma glass: vPLASMA's device/protocol core, plus its
+         canvas control compiled in directly (shared file, not a library —
+         VPlasma.Core stays UI-free). -->
+    <ProjectReference Include="..\VPlasma.Core\VPlasma.Core.csproj" />
+    <Compile Include="..\VPlasma.App\PlasmaCanvas.cs" Link="PlasmaCanvas.cs" />
   </ItemGroup>
 
   <!-- Stamp commit date + short sha into InformationalVersion; the window

src/VRio.Core/Device/PipeFraming.cs

@@ -0,0 +1,134 @@
+namespace VRio.Core.Device;
+
+/// <summary>
+/// The framing shared with the DOSBox-X fork's <c>namedpipe</c> serial
+/// backend (its <c>serialnamedpipe.h</c> header comment is the contract's
+/// source of truth on that side). A pipe is a plain byte stream, so serial
+/// data and modem control lines are multiplexed as typed frames:
+///
+/// <code>
+///   0x00 &lt;len:u8&gt; &lt;len bytes&gt;   serial data, len ≥ 1 (batching allowed)
+///   0x01 &lt;lines:u8&gt;             the sender's OWN output lines (bit0 DTR,
+///                                bit1 RTS); the receiver applies the
+///                                null-modem cross: peer DTR → local DSR,
+///                                peer RTS → local CTS
+/// </code>
+///
+/// Each side sends one lines frame immediately on connect; until it arrives
+/// the peer's lines are assumed low, and a disconnect drops them low again.
+/// Any other frame type is a protocol bug, not line noise — pipes don't drop
+/// bytes — so the receiver logs it and drops the connection instead of
+/// trying to resync.
+/// </summary>
+public static class PipeFraming
+{
+    public const byte DataType = 0x00;
+    public const byte LinesType = 0x01;
+
+    /// <summary>Lines-frame bit: the sender's DTR output.</summary>
+    public const byte LineDtr = 0x01;
+
+    /// <summary>Lines-frame bit: the sender's RTS output.</summary>
+    public const byte LineRts = 0x02;
+
+    /// <summary>Both outputs asserted — what a present, powered device reports.</summary>
+    public const byte LinesPresent = LineDtr | LineRts;
+
+    /// <summary>Build a lines frame carrying <paramref name="lines"/>.</summary>
+    public static byte[] EncodeLines(byte lines) => new[] { LinesType, lines };
+}
+
+/// <summary>
+/// Incremental decoder for <see cref="PipeFraming"/>: feed it raw pipe reads,
+/// get one <see cref="Data"/> event per complete data frame and one
+/// <see cref="Lines"/> event per lines frame. Frames may split across reads
+/// at any byte boundary. A malformed stream (unknown type, zero-length data
+/// frame) poisons the decoder: <see cref="Feed"/> returns false and
+/// <see cref="Violation"/> says why — drop the connection and
+/// <see cref="Reset"/> before serving the next one.
+/// </summary>
+public sealed class PipeFrameDecoder
+{
+    private enum State { Type, Length, Payload, Lines }
+
+    private readonly byte[] _payload = new byte[byte.MaxValue];
+    private State _state;
+    private int _fill, _length;
+
+    /// <summary>
+    /// A complete data frame's payload as (buffer, count). The buffer is
+    /// reused across frames — consume it synchronously.
+    /// </summary>
+    public event Action<byte[], int>? Data;
+
+    /// <summary>A lines frame's bits (see <see cref="PipeFraming.LineDtr"/>).</summary>
+    public event Action<byte>? Lines;
+
+    /// <summary>Why the stream was rejected, or null while it is healthy.</summary>
+    public string? Violation { get; private set; }
+
+    /// <summary>Forget any partial frame and clear a violation (new connection).</summary>
+    public void Reset()
+    {
+        _state = State.Type;
+        _fill = _length = 0;
+        Violation = null;
+    }
+
+    /// <summary>
+    /// Consume <paramref name="count"/> received bytes from
+    /// <paramref name="buffer"/>. Returns false when the stream violates the
+    /// framing contract (see <see cref="Violation"/>); a poisoned decoder
+    /// keeps returning false until <see cref="Reset"/>.
+    /// </summary>
+    public bool Feed(byte[] buffer, int count)
+    {
+        if (Violation is not null)
+            return false;
+
+        for (int i = 0; i < count; i++)
+        {
+            byte b = buffer[i];
+            switch (_state)
+            {
+                case State.Type when b == PipeFraming.DataType:
+                    _state = State.Length;
+                    break;
+
+                case State.Type when b == PipeFraming.LinesType:
+                    _state = State.Lines;
+                    break;
+
+                case State.Type:
+                    Violation = $"unknown frame type 0x{b:X2}";
+                    return false;
+
+                case State.Length when b == 0:
+                    Violation = "zero-length data frame";
+                    return false;
+
+                case State.Length:
+                    _length = b;
+                    _fill = 0;
+                    _state = State.Payload;
+                    break;
+
+                case State.Payload:
+                    _payload[_fill++] = b;
+                    if (_fill == _length)
+                    {
+                        _state = State.Type;
+                        Data?.Invoke(_payload, _length);
+                    }
+                    break;
+
+                case State.Lines:
+                    _state = State.Type;
+                    Lines?.Invoke(b);
+                    break;
+            }
+        }
+
+        return true;
+    }
+}

src/VRio.Core/Device/VRioPipeService.cs

@@ -0,0 +1,392 @@
+using System.Diagnostics;
+using System.IO.Pipes;
+using System.Runtime.InteropServices;
+
+namespace VRio.Core.Device;
+
+/// <summary>
+/// Serves a <see cref="VRioDevice"/> over the named pipe that the DOSBox-X
+/// fork's <c>serial1=namedpipe pipe:vrio</c> backend connects to — the
+/// com0com-free transport. vRIO is the pipe <em>server</em> (the device is
+/// always present); DOSBox-X is the client and background-retries while the
+/// pipe is missing, so this service listens for the whole app lifetime
+/// alongside the COM path at no cost. An unconnected pipe is an unplugged
+/// cable: the device keeps running, transmit bytes fall on the floor.
+///
+/// <para>Framing per <see cref="PipeFraming"/>. On connect we immediately
+/// send our lines frame (DTR+RTS high — "board present", the same lines the
+/// serial path asserts via DtrEnable/RtsEnable); the peer's DTR edges surface
+/// through <see cref="HostHandshake"/> exactly like the DSR blips through a
+/// null modem, and a disconnect drops all lines low. The game hardware-resets
+/// the RIO by pulsing DTR, and the in-band lines frames keep that edge's
+/// position in the byte stream — the reason the contract multiplexes control
+/// onto the data pipe instead of using a second one.</para>
+///
+/// <para>Outbound bytes are paced one per 10-bit frame time exactly like
+/// <see cref="VRioSerialService"/> (see its remarks for the full rationale).
+/// With the 9600-baud wire gone, this pacer is the only thing standing
+/// between the host and an impossible burst, so each paced byte travels as
+/// its own 3-byte data frame and the inter-byte timing survives the pipe.</para>
+/// </summary>
+public sealed class VRioPipeService : IDisposable
+{
+    /// <summary>The contract pipe name: DOSBox-X connects to <c>\\.\pipe\vrio</c>.</summary>
+    public const string DefaultPipeName = "vrio";
+
+    // Pacing mirrors VRioSerialService: one byte per 10-bit frame at 9600
+    // baud; sleep until ~1.8 ms from the slot, then spin the remainder.
+    private static readonly long BytePeriodTicks = Stopwatch.Frequency * 10 / VRioSerialService.BaudRate;
+    private static readonly long SpinThresholdTicks = Stopwatch.Frequency * 18 / 10_000;
+
+    private readonly VRioDevice _device;
+    private readonly string _pipeName;
+    private readonly object _txGate = new();
+    private readonly Queue<byte> _txQueue = new();
+    private readonly PipeFrameDecoder _decoder = new();
+
+    private NamedPipeServerStream? _pipe;
+    private Thread? _server;
+    private Thread? _writer;
+    private volatile bool _running;
+    private volatile bool _clientConnected;
+    private bool _peerDtr, _peerRts;
+    private bool _timerResolutionRaised;
+
+    public VRioPipeService(VRioDevice device, string pipeName = DefaultPipeName)
+    {
+        _device = device ?? throw new ArgumentNullException(nameof(device));
+        if (string.IsNullOrWhiteSpace(pipeName))
+            throw new ArgumentException("Pipe name is required.", nameof(pipeName));
+        _pipeName = pipeName;
+
+        _device.Transmit += Write;
+        _decoder.Data += (buffer, count) => _device.OnReceived(buffer, count);
+        _decoder.Lines += OnPeerLines;
+    }
+
+    /// <summary>The served pipe name (without the <c>\\.\pipe\</c> prefix).</summary>
+    public string PipeName => _pipeName;
+
+    /// <summary>True while the server is up (whether or not a client is connected).</summary>
+    public bool IsListening => _running;
+
+    /// <summary>True while a client is connected.</summary>
+    public bool IsClientConnected => _clientConnected;
+
+    /// <summary>A client connected (true) or went away (false).</summary>
+    public event Action<bool>? ClientChanged;
+
+    /// <summary>
+    /// The host's DTR line changed (the game pulses it to hardware-reset the
+    /// board). Same semantics as <see cref="VRioSerialService.HostHandshake"/>:
+    /// the argument is the new line state as seen on our DSR pin.
+    /// </summary>
+    public event Action<bool>? HostHandshake;
+
+    /// <summary>Pipe-level log lines (listen/connect/errors).</summary>
+    public event Action<string>? Logged;
+
+    /// <summary>Start listening (idempotent). Clients may come and go forever.</summary>
+    public void Start()
+    {
+        if (_running)
+            return;
+
+        _running = true;
+        lock (_txGate) _txQueue.Clear();
+
+        _server = new Thread(ServerLoop) { IsBackground = true, Name = $"vRIO pipe server ({_pipeName})" };
+        _server.Start();
+        _writer = new Thread(WriteLoop) { IsBackground = true, Name = $"vRIO pipe writer ({_pipeName})" };
+        _writer.Start();
+
+        Logged?.Invoke($@"Listening on \\.\pipe\{_pipeName} (TX paced at the wire rate) — DOSBox-X connects when it boots");
+    }
+
+    /// <summary>Stop listening and drop any client (idempotent).</summary>
+    public void Stop()
+    {
+        if (!_running)
+            return;
+
+        _running = false;
+        lock (_txGate)
+        {
+            _txQueue.Clear();
+            Monitor.PulseAll(_txGate); // wake the writer so it can exit
+        }
+
+        NamedPipeServerStream? pipe = _pipe;
+        _pipe = null;
+        try { pipe?.Dispose(); }
+        catch (IOException) { }
+
+        // A WaitForConnection pending on the disposed stream can survive the
+        // Dispose on net48; a throwaway client connect releases it either way.
+        try
+        {
+            using var poke = new NamedPipeClientStream(".", _pipeName, PipeDirection.Out);
+            poke.Connect(100);
+        }
+        catch (Exception ex) when (ex is IOException or TimeoutException or UnauthorizedAccessException) { }
+
+        _server?.Join(1000);
+        _server = null;
+        _writer?.Join(1000);
+        _writer = null;
+
+        if (_timerResolutionRaised)
+        {
+            timeEndPeriod(1);
+            _timerResolutionRaised = false;
+        }
+        _clientConnected = false;
+
+        Logged?.Invoke("Pipe server stopped");
+    }
+
+    private void ServerLoop()
+    {
+        bool busyLogged = false; // log the name collision once, not per retry
+
+        while (_running)
+        {
+            NamedPipeServerStream pipe;
+            try
+            {
+                pipe = new NamedPipeServerStream(_pipeName, PipeDirection.InOut, 1,
+                    PipeTransmissionMode.Byte, PipeOptions.Asynchronous);
+            }
+            catch (Exception ex) when (ex is IOException or UnauthorizedAccessException)
+            {
+                // Name already served — most likely a second vRIO instance.
+                if (!busyLogged)
+                {
+                    busyLogged = true;
+                    Logged?.Invoke($@"\\.\pipe\{_pipeName} is busy ({ex.Message.TrimEnd('.')}) — retrying until it frees up");
+                }
+                for (int i = 0; i < 20 && _running; i++)
+                    Thread.Sleep(100);
+                continue;
+            }
+            busyLogged = false;
+
+            _pipe = pipe;
+            try
+            {
+                pipe.WaitForConnection();
+            }
+            catch (Exception ex) when (ex is IOException or ObjectDisposedException or InvalidOperationException)
+            {
+                // Disposed by Stop(), or a client vanished mid-connect.
+                _pipe = null;
+                try { pipe.Dispose(); }
+                catch (IOException) { }
+                continue;
+            }
+
+            if (!_running || !OnClientConnected(pipe))
+            {
+                _pipe = null;
+                try { pipe.Dispose(); }
+                catch (IOException) { }
+                continue;
+            }
+
+            ReadUntilDisconnect(pipe);
+
+            OnClientDisconnected();
+            _pipe = null;
+            try { pipe.Dispose(); }
+            catch (IOException) { }
+        }
+    }
+
+    /// <summary>Per-connection setup; false if the client died before it finished.</summary>
+    private bool OnClientConnected(NamedPipeServerStream pipe)
+    {
+        _decoder.Reset();
+        _peerDtr = _peerRts = false;
+        lock (_txGate) _txQueue.Clear();
+
+        // Our lines frame goes first, before the writer can interleave data
+        // (it only writes once _clientConnected flips below): DTR+RTS high,
+        // board present — the peer maps them to its DSR/CTS.
+        try
+        {
+            byte[] lines = PipeFraming.EncodeLines(PipeFraming.LinesPresent);
+            pipe.Write(lines, 0, lines.Length);
+            pipe.Flush();
+        }
+        catch (Exception ex) when (ex is IOException or ObjectDisposedException or InvalidOperationException)
+        {
+            return false;
+        }
+
+        // 1 ms system timer resolution while a client is connected, so the
+        // pacer's Thread.Sleep(1) actually sleeps ~1 ms.
+        _timerResolutionRaised = timeBeginPeriod(1) == 0;
+        _clientConnected = true;
+
+        Logged?.Invoke("Pipe client connected — sent lines DTR+RTS (board present)");
+        ClientChanged?.Invoke(true);
+        return true;
+    }
+
+    private void OnClientDisconnected()
+    {
+        _clientConnected = false;
+        lock (_txGate) _txQueue.Clear();
+
+        if (_timerResolutionRaised)
+        {
+            timeEndPeriod(1);
+            _timerResolutionRaised = false;
+        }
+
+        // Contract: a disconnect drops all lines low on the surviving side.
+        if (_peerDtr)
+        {
+            _peerDtr = false;
+            HostHandshake?.Invoke(false);
+        }
+        _peerRts = false;
+
+        if (_running)
+        {
+            Logged?.Invoke("Pipe client disconnected");
+            ClientChanged?.Invoke(false);
+        }
+    }
+
+    private void ReadUntilDisconnect(NamedPipeServerStream pipe)
+    {
+        var buffer = new byte[512];
+        while (_running)
+        {
+            int n;
+            try
+            {
+                n = pipe.Read(buffer, 0, buffer.Length);
+            }
+            catch (Exception ex) when (ex is IOException or ObjectDisposedException or InvalidOperationException or OperationCanceledException)
+            {
+                if (_running)
+                    Logged?.Invoke($"Pipe error: {ex.Message}");
+                return;
+            }
+
+            if (n == 0)
+                return; // client closed its end
+
+            if (!_decoder.Feed(buffer, n))
+            {
+                Logged?.Invoke($"Pipe protocol violation: {_decoder.Violation} — dropping the connection");
+                return;
+            }
+        }
+    }
+
+    private void OnPeerLines(byte lines)
+    {
+        _peerRts = (lines & PipeFraming.LineRts) != 0; // tracked; nothing consumes CTS today
+        bool dtr = (lines & PipeFraming.LineDtr) != 0;
+        if (dtr == _peerDtr)
+            return;
+
+        _peerDtr = dtr;
+        HostHandshake?.Invoke(dtr);
+    }
+
+    // The device's Transmit handler: queue the frame for the paced writer so
+    // the caller (UI click, reader thread mid-reply) never blocks on the pipe.
+    private void Write(byte[] data)
+    {
+        if (!_running || !_clientConnected)
+            return; // no host on the pipe — a real UART shifts into an unterminated line
+
+        lock (_txGate)
+        {
+            foreach (byte b in data)
+                _txQueue.Enqueue(b);
+            Monitor.Pulse(_txGate);
+        }
+    }
+
+    private void WriteLoop()
+    {
+        // One data frame per paced byte, so the pipe carries the same
+        // inter-byte spacing a 9600-baud wire would.
+        var frame = new byte[] { PipeFraming.DataType, 1, 0 };
+        long slot = Stopwatch.GetTimestamp();
+
+        while (_running)
+        {
+            lock (_txGate)
+            {
+                while (_txQueue.Count == 0)
+                {
+                    if (!_running)
+                        return;
+                    Monitor.Wait(_txGate, 200); // timed, so a missed pulse can't wedge shutdown
+                }
+                frame[2] = _txQueue.Dequeue();
+            }
+
+            // This byte's wire slot: one frame after the previous byte, or now
+            // if the line has been idle (no burst "catch-up" debt).
+            slot = Math.Max(slot + BytePeriodTicks, Stopwatch.GetTimestamp());
+            PaceUntil(slot);
+
+            NamedPipeServerStream? pipe = _pipe;
+            if (pipe is null || !_clientConnected)
+                continue; // client left while this byte waited its slot — it's stale, drop it
+
+            try
+            {
+                pipe.Write(frame, 0, frame.Length);
+                pipe.Flush();
+            }
+            catch (Exception ex) when (ex is IOException or ObjectDisposedException or InvalidOperationException)
+            {
+                // The client died mid-write; the backlog is already stale.
+                // Drop it and keep serving — the server loop notices the EOF
+                // and cycles back to WaitForConnection.
+                lock (_txGate) _txQueue.Clear();
+                continue;
+            }
+
+            // If the wait overshot its slot, pace the next byte from the
+            // actual emission instead — a stall must not cause a catch-up burst.
+            long now = Stopwatch.GetTimestamp();
+            if (now > slot)
+                slot = now;
+        }
+    }
+
+    private static void PaceUntil(long slotTicks)
+    {
+        while (true)
+        {
+            long remaining = slotTicks - Stopwatch.GetTimestamp();
+            if (remaining <= 0)
+                return;
+            if (remaining > SpinThresholdTicks)
+                Thread.Sleep(1);
+            else
+                Thread.SpinWait(64);
+        }
+    }
+
+    [DllImport("winmm.dll")]
+    private static extern uint timeBeginPeriod(uint uMilliseconds);
+
+    [DllImport("winmm.dll")]
+    private static extern uint timeEndPeriod(uint uMilliseconds);
+
+    public void Dispose()
+    {
+        _device.Transmit -= Write;
+        Stop();
+    }
+}

src/VRio.Core/VRio.Core.csproj

@@ -12,7 +12,6 @@
 
   <ItemGroup>
     <PackageReference Include="System.Memory" Version="4.5.5" />
-    <PackageReference Include="Microsoft.Bcl.HashCode" Version="1.1.1" />
     <PackageReference Include="PolySharp" Version="1.14.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>

tests/VPlasma.Core.Tests/VPlasmaPipeServiceTests.cs

@@ -0,0 +1,99 @@
+using System.Diagnostics;
+using System.IO.Pipes;
+using VPlasma.Core.Device;
+using Xunit;
+
+namespace VPlasma.Core.Tests;
+
+public class VPlasmaPipeServiceTests
+{
+    private static string UniqueName() => $"vplasma-test-{Guid.NewGuid():N}";
+
+    private static void WaitFor(Func<bool> condition, int timeoutMs = 2000)
+    {
+        var clock = Stopwatch.StartNew();
+        while (!condition())
+        {
+            Assert.True(clock.ElapsedMilliseconds < timeoutMs, "timed out waiting for a condition");
+            Thread.Sleep(10);
+        }
+    }
+
+    private static NamedPipeClientStream Connect(string name)
+    {
+        var pipe = new NamedPipeClientStream(".", name, PipeDirection.InOut, PipeOptions.Asynchronous);
+        var clock = Stopwatch.StartNew();
+        while (true)
+        {
+            try
+            {
+                pipe.Connect(200);
+                return pipe;
+            }
+            catch (Exception ex) when (ex is IOException or TimeoutException)
+            {
+                if (clock.ElapsedMilliseconds >= 3000)
+                    throw;
+                Thread.Sleep(25);
+            }
+        }
+    }
+
+    [Fact]
+    public void Framed_text_reaches_the_display_and_lines_are_ignored()
+    {
+        string name = UniqueName();
+        var device = new VPlasmaDevice();
+        using var service = new VPlasmaPipeService(device, name);
+        service.Start();
+
+        using var client = Connect(name);
+        var hello = new byte[2];
+        Assert.Equal(1, client.Read(hello, 0, 1)); // on-connect lines frame,
+        Assert.Equal(1, client.Read(hello, 1, 1)); // possibly split
+        Assert.Equal(new byte[] { 0x01, 0x03 }, hello); // DTR+RTS: display present
+
+        // RTS chatter (DOS console redirection toggles it per byte) then "HI",
+        // the data frame torn in half mid-payload.
+        client.Write(new byte[] { 0x01, 0x02, 0x00, 0x02, (byte)'H' }, 0, 5);
+        client.Flush();
+        Thread.Sleep(20);
+        client.Write(new byte[] { (byte)'I' }, 0, 1);
+        client.Flush();
+
+        WaitFor(() => device.BytesReceived == 2);
+        Assert.Equal(2, device.TextCharsDrawn);
+    }
+
+    [Fact]
+    public async Task Unknown_frame_type_drops_the_client_and_server_recovers()
+    {
+        string name = UniqueName();
+        var device = new VPlasmaDevice();
+        using var service = new VPlasmaPipeService(device, name);
+        service.Start();
+
+        using (var bad = Connect(name))
+        {
+            var hello = new byte[2];
+            bad.Read(hello, 0, 2);
+            bad.Write(new byte[] { 0x7F }, 0, 1); // not a frame type
+            bad.Flush();
+            // Contract: log + drop, no resync — our next read sees the close.
+            var eof = Task.Run(() =>
+            {
+                try { return bad.Read(new byte[1], 0, 1) == 0; }
+                catch (IOException) { return true; }
+            });
+            Assert.True(await Task.WhenAny(eof, Task.Delay(2000)) == eof,
+                "server did not drop the connection");
+            Assert.True(await eof);
+        }
+
+        using var good = Connect(name);
+        var again = new byte[2];
+        Assert.Equal(1, good.Read(again, 0, 1));
+        Assert.Equal(1, good.Read(again, 1, 1));
+        Assert.Equal(new byte[] { 0x01, 0x03 }, again);
+    }
+}

tests/VRio.Core.Tests/PipeServiceTests.cs

@@ -0,0 +1,327 @@
+using System.Diagnostics;
+using System.IO.Pipes;
+using VRio.Core.Device;
+using VRio.Core.Protocol;
+using Xunit;
+
+namespace VRio.Core.Tests;
+
+public class PipeFrameDecoderTests
+{
+    [Fact]
+    public void Data_frame_delivers_payload()
+    {
+        var decoder = new PipeFrameDecoder();
+        byte[]? got = null;
+        decoder.Data += (buf, count) => got = buf.Take(count).ToArray();
+
+        Assert.True(decoder.Feed(new byte[] { 0x00, 0x03, 0xAA, 0xBB, 0xCC }, 5));
+        Assert.Equal(new byte[] { 0xAA, 0xBB, 0xCC }, got);
+    }
+
+    [Fact]
+    public void Frames_survive_any_split_across_reads()
+    {
+        var decoder = new PipeFrameDecoder();
+        var data = new List<byte>();
+        var lines = new List<byte>();
+        decoder.Data += (buf, count) => data.AddRange(buf.Take(count));
+        decoder.Lines += lines.Add;
+
+        // A lines frame, a 2-byte data frame, a 1-byte data frame — one byte at a time.
+        byte[] stream = { 0x01, 0x03, 0x00, 0x02, 0x81, 0x01, 0x00, 0x01, 0xFC };
+        foreach (byte b in stream)
+            Assert.True(decoder.Feed(new[] { b }, 1));
+
+        Assert.Equal(new byte[] { 0x03 }, lines);
+        Assert.Equal(new byte[] { 0x81, 0x01, 0xFC }, data);
+    }
+
+    [Fact]
+    public void Multiple_frames_in_one_read_all_deliver()
+    {
+        var decoder = new PipeFrameDecoder();
+        var data = new List<byte>();
+        var lines = new List<byte>();
+        decoder.Data += (buf, count) => data.AddRange(buf.Take(count));
+        decoder.Lines += lines.Add;
+
+        byte[] chunk = { 0x00, 0x01, 0x42, 0x01, 0x00, 0x00, 0x01, 0x43 };
+        Assert.True(decoder.Feed(chunk, chunk.Length));
+
+        Assert.Equal(new byte[] { 0x42, 0x43 }, data);
+        Assert.Equal(new byte[] { 0x00 }, lines);
+    }
+
+    [Fact]
+    public void Unknown_frame_type_poisons_the_decoder()
+    {
+        var decoder = new PipeFrameDecoder();
+
+        Assert.False(decoder.Feed(new byte[] { 0x7F }, 1));
+        Assert.Contains("0x7F", decoder.Violation);
+        // Poisoned: even a healthy frame is rejected until Reset.
+        Assert.False(decoder.Feed(new byte[] { 0x00, 0x01, 0x42 }, 3));
+
+        decoder.Reset();
+        Assert.Null(decoder.Violation);
+        Assert.True(decoder.Feed(new byte[] { 0x00, 0x01, 0x42 }, 3));
+    }
+
+    [Fact]
+    public void Zero_length_data_frame_is_a_violation()
+    {
+        var decoder = new PipeFrameDecoder();
+        Assert.False(decoder.Feed(new byte[] { 0x00, 0x00 }, 2));
+        Assert.Contains("zero-length", decoder.Violation);
+    }
+}
+
+public class VRioPipeServiceTests
+{
+    /// <summary>
+    /// A contract-speaking client: connects to the service's pipe, deframes
+    /// everything it receives (timestamping data bytes for the pacing test),
+    /// and sends raw frame bytes.
+    /// </summary>
+    private sealed class TestClient : IDisposable
+    {
+        private readonly NamedPipeClientStream _pipe;
+        private readonly Thread _reader;
+        private readonly object _sync = new();
+        private readonly List<byte> _data = new();
+        private readonly List<long> _dataTicks = new();
+        private readonly List<byte> _lines = new();
+        private volatile bool _closed;
+
+        public TestClient(string pipeName)
+        {
+            _pipe = new NamedPipeClientStream(".", pipeName, PipeDirection.InOut,
+                PipeOptions.Asynchronous);
+
+            // The server's listener may still be spinning up; retry briefly.
+            var connectClock = Stopwatch.StartNew();
+            while (true)
+            {
+                try
+                {
+                    _pipe.Connect(200);
+                    break;
+                }
+                catch (Exception ex) when (ex is IOException or TimeoutException)
+                {
+                    if (connectClock.ElapsedMilliseconds >= 3000)
+                        throw;
+                    Thread.Sleep(25);
+                }
+            }
+
+            var decoder = new PipeFrameDecoder();
+            decoder.Data += (buf, count) =>
+            {
+                long now = Stopwatch.GetTimestamp();
+                lock (_sync)
+                    for (int i = 0; i < count; i++)
+                    {
+                        _data.Add(buf[i]);
+                        _dataTicks.Add(now);
+                    }
+            };
+            decoder.Lines += b => { lock (_sync) _lines.Add(b); };
+
+            _reader = new Thread(() =>
+            {
+                var buffer = new byte[512];
+                while (true)
+                {
+                    int n;
+                    try { n = _pipe.Read(buffer, 0, buffer.Length); }
+                    catch (Exception ex) when (ex is IOException or ObjectDisposedException) { break; }
+                    if (n == 0 || !decoder.Feed(buffer, n))
+                        break;
+                }
+                _closed = true;
+            })
+            { IsBackground = true };
+            _reader.Start();
+        }
+
+        public bool Closed => _closed;
+        public byte[] Data { get { lock (_sync) return _data.ToArray(); } }
+        public long[] DataTicks { get { lock (_sync) return _dataTicks.ToArray(); } }
+        public byte[] Lines { get { lock (_sync) return _lines.ToArray(); } }
+
+        public void SendRaw(params byte[] bytes)
+        {
+            _pipe.Write(bytes, 0, bytes.Length);
+            _pipe.Flush();
+        }
+
+        public void SendData(byte[] payload)
+        {
+            var frame = new byte[2 + payload.Length];
+            frame[0] = PipeFraming.DataType;
+            frame[1] = (byte)payload.Length;
+            payload.CopyTo(frame, 2);
+            SendRaw(frame);
+        }
+
+        public void Dispose()
+        {
+            _pipe.Dispose();
+            _reader.Join(1000);
+        }
+    }
+
+    private static string UniqueName() => $"vrio-test-{Guid.NewGuid():N}";
+
+    private static void WaitFor(Func<bool> condition, int timeoutMs = 2000)
+    {
+        var clock = Stopwatch.StartNew();
+        while (!condition())
+        {
+            Assert.True(clock.ElapsedMilliseconds < timeoutMs, "timed out waiting for a condition");
+            Thread.Sleep(10);
+        }
+    }
+
+    [Fact]
+    public void Client_gets_board_present_lines_on_connect()
+    {
+        string name = UniqueName();
+        var device = new VRioDevice();
+        using var service = new VRioPipeService(device, name);
+        service.Start();
+
+        using var client = new TestClient(name);
+        WaitFor(() => client.Lines.Length > 0);
+
+        Assert.Equal(PipeFraming.LinesPresent, client.Lines[0]); // DTR+RTS: board present
+    }
+
+    [Fact]
+    public void Peer_dtr_edges_surface_as_host_handshake()
+    {
+        string name = UniqueName();
+        var device = new VRioDevice();
+        using var service = new VRioPipeService(device, name);
+        var edges = new List<bool>();
+        service.HostHandshake += high => { lock (edges) edges.Add(high); };
+        service.Start();
+
+        using var client = new TestClient(name);
+        client.SendRaw(PipeFraming.LinesType, PipeFraming.LineDtr); // DTR up
+        client.SendRaw(PipeFraming.LinesType, 0x00);                // DTR down (the reset pulse)
+
+        WaitFor(() => { lock (edges) return edges.Count == 2; });
+        lock (edges)
+            Assert.Equal(new[] { true, false }, edges);
+    }
+
+    [Fact]
+    public void Version_request_round_trips_ack_then_reply()
+    {
+        string name = UniqueName();
+        var device = new VRioDevice();
+        using var service = new VRioPipeService(device, name);
+        service.Start();
+
+        using var client = new TestClient(name);
+        WaitFor(() => client.Lines.Length > 0); // fully connected
+        client.SendData(PacketBuilder.Build(RioCommand.VersionRequest));
+
+        byte[] expected = new[] { (byte)RioControl.Ack }
+            .Concat(PacketBuilder.VersionReply(4, 2)).ToArray();
+        WaitFor(() => client.Data.Length >= expected.Length);
+
+        Assert.Equal(expected, client.Data);
+    }
+
+    [Fact]
+    public void Reply_bytes_are_paced_at_the_wire_rate()
+    {
+        string name = UniqueName();
+        var device = new VRioDevice();
+        using var service = new VRioPipeService(device, name);
+        service.Start();
+
+        using var client = new TestClient(name);
+        WaitFor(() => client.Lines.Length > 0);
+        client.SendData(PacketBuilder.Build(RioCommand.VersionRequest));
+
+        // ACK + 4-byte VersionReply = 5 bytes = 4 inter-byte gaps ≈ 4.2 ms at
+        // 9600 baud. An unpaced writer would land them in well under 1 ms.
+        WaitFor(() => client.Data.Length >= 5);
+        long[] ticks = client.DataTicks;
+        double spanMs = (ticks[4] - ticks[0]) * 1000.0 / Stopwatch.Frequency;
+
+        Assert.True(spanMs >= 2.5, $"5 reply bytes arrived in {spanMs:F2} ms — pipe TX is not paced");
+    }
+
+    [Fact]
+    public void Unknown_frame_type_drops_the_client_and_server_recovers()
+    {
+        string name = UniqueName();
+        var device = new VRioDevice();
+        using var service = new VRioPipeService(device, name);
+        service.Start();
+
+        using (var bad = new TestClient(name))
+        {
+            WaitFor(() => bad.Lines.Length > 0);
+            bad.SendRaw(0x7F); // not a frame type
+            WaitFor(() => bad.Closed); // contract: log + drop, no resync
+        }
+
+        // The listener must come back for the next client.
+        using var good = new TestClient(name);
+        WaitFor(() => good.Lines.Length > 0);
+        Assert.Equal(PipeFraming.LinesPresent, good.Lines[0]);
+    }
+
+    [Fact]
+    public void Client_disconnect_drops_dtr_low()
+    {
+        string name = UniqueName();
+        var device = new VRioDevice();
+        using var service = new VRioPipeService(device, name);
+        var edges = new List<bool>();
+        service.HostHandshake += high => { lock (edges) edges.Add(high); };
+        service.Start();
+
+        using (var client = new TestClient(name))
+        {
+            client.SendRaw(PipeFraming.LinesType, PipeFraming.LineDtr);
+            WaitFor(() => { lock (edges) return edges.Count == 1; });
+        } // client leaves with DTR still high
+
+        WaitFor(() => { lock (edges) return edges.Count == 2; });
+        lock (edges)
+            Assert.Equal(new[] { true, false }, edges);
+    }
+
+    [Fact]
+    public void Data_split_mid_frame_still_reaches_the_device()
+    {
+        string name = UniqueName();
+        var device = new VRioDevice();
+        using var service = new VRioPipeService(device, name);
+        var lamps = new List<(int Address, byte State)>();
+        device.LampChanged += (address, state) => { lock (lamps) lamps.Add((address, state)); };
+        service.Start();
+
+        using var client = new TestClient(name);
+        WaitFor(() => client.Lines.Length > 0);
+
+        // LampRequest 0x00 ← 0x01, framed, then torn in half mid-payload.
+        byte[] packet = PacketBuilder.Build(RioCommand.LampRequest, new byte[] { 0x00, 0x01 });
+        var frame = new byte[] { PipeFraming.DataType, (byte)packet.Length }.Concat(packet).ToArray();
+        client.SendRaw(frame.Take(3).ToArray());
+        Thread.Sleep(20);
+        client.SendRaw(frame.Skip(3).ToArray());
+
+        WaitFor(() => { lock (lamps) return lamps.Count == 1; });
+        lock (lamps)
+            Assert.Equal((0x00, (byte)0x01), lamps[0]);
+    }
+}