Periphery.Bootloader 4.1.0-alpha.2

Periphery

A modern, cross-platform .NET library for discovering hardware devices — USB, Bluetooth, network adapters, displays, and more — with a clean, LINQ-friendly API.

Windows, Linux, and macOS providers are complete.

Why Periphery?

Enumerating connected hardware today means reaching for platform-specific APIs — SetupAPI on Windows, udev on Linux, IOKit on macOS — each with its own conventions and quirks. Periphery provides a single high-level surface that abstracts those differences away so you can:

• Discover devices by category (USB, Bluetooth, Display, Network, ...) with one API.
• Query devices using familiar LINQ expressions.
• Monitor arrival, departure, activation, and deactivation via events.
• Write cross-platform code that just works on Windows, Linux, and macOS.

The core library focuses on discovery — it tells you what's plugged in. Protocol-level I/O lives in companion extension libraries layered on the same device model. Keeping the core enumeration-only holds its runtime dependency surface to a single abstractions package (Microsoft.Extensions.Logging.Abstractions); the extensions opt into real device communication when you need it.

Extensions are Windows + Linux. Enumeration works on all three platforms, but the I/O extensions ship Windows and Linux backends only — CameraDevice, HidDevice, UsbDevice, and MonitorDevice throw PlatformNotSupportedException on macOS. The AVFoundation and IOKit HID/USB backends are planned, not written.

Quick Look

// One-shot: all active USB devices
var usb = await Devices.Enumerate()
    .OfCategory(DeviceCategory.Usb)
    .Active()
    .ToListAsync();

foreach (var device in usb)
    Console.WriteLine($"{device.Name} ({device.Id})");

// Fluent query with LINQ
var mice = await Devices.Enumerate()
    .OfCategory(DeviceCategory.Hid)
    .WithName("Mouse")
    .ByManufacturer("Logitech")
    .OrderBy(d => d.Name)
    .Take(5)
    .ToListAsync();

// USB VID/PID lookup
var specific = await Devices.Enumerate()
    .OfCategory(DeviceCategory.Usb)
    .WithUsbId("1234", "5678")
    .FirstOrDefaultAsync();

// IAsyncEnumerable — works with await foreach
await foreach (var device in Devices.Enumerate().OfCategory(DeviceCategory.Network))
    Console.WriteLine($"{device.Name} ({device.BusType})");

// Real-time monitoring
await using var watcher = Devices.Watch()
    .OfCategory(DeviceCategory.Bluetooth);

// Two orthogonal transitions: presence in the OS device tree, and activity.
watcher.Appeared    += (_, e) => Console.WriteLine($"+ appeared:    {e.Device.Name}");
watcher.Activated   += (_, e) => Console.WriteLine($"+ activated:   {e.Device.Name}");
watcher.Deactivated += (_, e) => Console.WriteLine($"- deactivated: {e.Device.Name}");
watcher.Disappeared += (_, e) => Console.WriteLine($"- disappeared: {e.Device.Name}");

await watcher.StartAsync();

// Per-device tracking — each tracker has dual state (IsPresent + IsActive)
await using var watcher = Devices.Watch();

var mouse   = watcher.AddTracker(t => t.OfCategory(DeviceCategory.Usb).WithUsbId("046D", "C52B"), name: "Mouse");
var airpods = watcher.AddTracker(t => t.OfCategory(DeviceCategory.Bluetooth).WithName("AirPods"), name: "AirPods");

// ActivityStatus starts at Unknown and settles once initial enumeration completes (ADR-0056).
mouse.StateChanged += (_, _) => Console.WriteLine($"Mouse: {mouse.ActivityStatus}");

await watcher.StartAsync();

// Trackers can be created upfront (e.g. from configuration) and attached later
var tracker = new DeviceTracker(t => t.OfCategory(DeviceCategory.Usb).WithUsbId("046D", "C52B"), name: "Mouse");
tracker.StateChanged += (_, _) => UpdateDashboard();

await using var watcher = Devices.Watch().AddTracker(tracker);
await watcher.StartAsync();

Device Categories

A category answers which OS subsystem surfaced this device — it's single-valued and drives enumeration routing (SetupAPI class GUID / udev subsystem / IOKit class). All providers are complete on all three platforms.

Capability Tags

A tag answers a different question — what can this device do? Tags are multi-valued, cross-cutting, and added by enrichers during enumeration; query them with WithTag(...). Five identifiers that used to be categories are now tags (ADR-0051), because each describes a capability a device has rather than the subsystem that surfaced it:

// "any scanner / still-image device", whichever subsystem it enumerated under
var scanners = await Devices.Enumerate().WithTag(DeviceTags.Imaging).ToListAsync();

// compose with a category to narrow the scan first
var receiptPrinter = await Devices.Enumerate()
    .OfCategory(DeviceCategory.Ports)      // a serial-attached printer
    .WithTag(DeviceTags.Printer)
    .FirstOrDefaultAsync();

🟡 Windows-first. The Windows class-GUID signals are live now, so each tag works on Windows exactly as the old category did. The Linux/macOS USB-class paths are written and dormant — they light up when cross-platform DeviceInfo.UsbClassCode population lands (deferred while Periphery builds out Windows depth first; see ADR-0051). Hid, Audio, and Battery are also available as capability tags emitted by enrichers (e.g. HID battery levels via Periphery.Hid).

OpenCV Without VideoCapture(0)

OpenCV has no camera identity model. VideoCapture(0) is an index into whatever order the operating system enumerated in, and it moves when a device is replugged, when a virtual camera installs itself, or when a laptop lid opens. On a machine with two identical cameras there is no argument you can pass that means the one on the left. Periphery already answers that question, for every device category, on all three platforms. The half that was missing was handing the pixels to OpenCV, and Periphery.Camera.OpenCvSharp is that half.

using OpenCvSharp;
using Periphery;
using Periphery.Camera;
using Periphery.Camera.OpenCvSharp;

// Pick the camera by what it is, not by where it landed in a list.
var device = await Devices.Enumerate()
    .OfCategory(DeviceCategory.Camera)
    .WithUsbId("046D", "0825")
    .FirstOrDefaultAsync()
    ?? throw new InvalidOperationException("That camera is not attached.");

var snapshot = await CameraDevice.ReadSnapshotAsync(device);
var format = snapshot.Formats
    .WithinBox(1280, 720)
    .PreferPixelFormat(CameraPixelFormat.Yuy2)
    .ThenByHighestFrameRate()
    .First();

await using var session = await CameraSession.OpenAsync(device, new CameraConfiguration(format));

await foreach (var frame in session.CaptureAsync())
{
    using (frame)
    using (var bgr = frame.ToBgr())     // any capture format -> CV_8UC3 BGR
    {
        Cv2.ImShow("preview", bgr);
        Cv2.WaitKey(1);
    }
}

No VideoCapture, no index, no format string. The camera was chosen by vendor and product ID; it could equally have been chosen by serial number, by name, by USB port path, or by a DeviceWatcher that hands you the camera the moment someone plugs it in.

Two identical cameras

This is the case the index model cannot express at all. Two of the same webcam report the same name and the same VID/PID, so the only thing that separates them is identity the OS assigns — a serial number if the device has one, and the physical port path if it does not.

var cameras = await Devices.Enumerate()
    .OfCategory(DeviceCategory.Camera)
    .WithName("HD Pro Webcam C920")
    .ToListAsync();

// Real UVC cameras usually carry a serial; the ones that don't are told apart
// by the port they are plugged into, which is stable across reboots.
var left  = cameras.Single(c => c.SerialNumber == "A1B2C3D4");
var right = cameras.Single(c => c.SerialNumber == "E5F6A7B8");

await using var leftSession  = await CameraSession.OpenAsync(left,  new CameraConfiguration(format));
await using var rightSession = await CameraSession.OpenAsync(right, new CameraConfiguration(format));

// Two sessions, two independent capture loops, each pinned to a known lens.

Assigning a stereo pair the wrong way round is not a crash; it is a depth map that is quietly inverted. An index cannot tell you which one you got, and a serial number can.

Three entry points, separated by who owns the pixels

AsMat is the default. Wrapping costs nothing measurable, and a 1080p YUY2 to BGR conversion is 0.126 ms against 1.83 ms for the clone ToMat has to make — copying "to be safe" is fourteen times the cost of the conversion it is supposedly protecting. The reason it returns a scope rather than a Mat is that frames are pooled: once the lease is released the buffer is handed to the next frame and refilled, and a Mat still pointing at it reads a later frame's pixels rather than faulting. A type you have to dispose puts that decision in the call-site syntax.

The native payload is yours to pick

Periphery.Camera.OpenCvSharp references OpenCvSharp4 — the managed binding — and no OpenCvSharp4.runtime.* package. Install the payload for the platform you deploy to: OpenCvSharp4.runtime.win on Windows, OpenCvSharp4.official.runtime.linux-x64 on Linux. macOS has no current first-party package — the newest is 4.6.0.20230105 against a 4.13 binding — so a macOS deployment needs a third-party build. Without a payload the package restores and compiles, and the first OpenCV call throws DllNotFoundException.

The package is named after the binding rather than the library, because OpenCvSharp4 and Emgu.CV are incompatible bindings of the same OpenCV and a Periphery.Camera.OpenCv would claim a name a future Emgu package could not share.

MJPEG

MJPEG is the default 1080p30 mode on most UVC webcams and it has no Mat shape, so the three methods split:

• AsMat throws. There is no header to build over a compressed blob, and therefore no zero-copy path to offer.
• ToMat throws. A byte-for-byte copy of JPEG is a 1 x n vector of encoded bytes, which is not what "a copy of the frame's pixels" should hand back.
• ToBgr decodes it, straight from the frame's span with no intermediate byte[]. This is what makes ToBgr total over every format a camera can deliver, and it is why the package has a third method rather than two.

Both refusals name ToBgr in the message. The one other refusal is Gray16 to BGR: narrowing 16 bits to 8 needs a range, and a fixed /257 renders most depth and IR sensors black — take the CV_16UC1 Mat and apply Cv2.Normalize or Cv2.ConvertScaleAbs yourself.

Do not hold the lease through inference

Convert inside the lease; do the slow work outside it.

await foreach (var frame in session.CaptureAsync())
{
    Mat bgr;
    using (frame)
        bgr = frame.ToBgr();        // ~0.1 ms, and the lease ends here

    await queue.Writer.WriteAsync(bgr);   // inference runs on the other side
}

A consumer slower than the frame interval parks the producer, because the session's delivery channel is BoundedChannelFullMode.Wait. Frames are then lost upstream inside Media Foundation or V4L2, where Periphery cannot count them: FramesDropped stays at zero while the delivered rate halves. That stall has no instrument today (#322), so the symptom is a frame rate that is quietly wrong rather than a warning in a log.

Requirements

• .NET 10 or later (libraries also ship a net8.0 target, offered best-effort — it is built but not covered by the test suite; see ADR-0069)
• Windows: No additional dependencies (uses SetupAPI and cfgmgr32 via P/Invoke)
• Linux: Requires libudev.so.1 (included in systemd-based distros; install libudev-dev or eudev-dev on minimal images). Periphery.Usb additionally requires libusb-1.0.so.0 >= 1.0.23 (libusb-1.0-0 on Debian/Ubuntu); Periphery.Hid and Periphery.Camera use the kernel ABIs directly (hidraw, V4L2) with no extra libraries. Device-node access typically needs udev rules or group membership (video for cameras; hidraw/usbfs rules for HID/USB - see ADR-0057).
• macOS: No additional dependencies (uses IOKit.framework and CoreFoundation.framework via P/Invoke)

Getting Started

git clone https://github.com/charles8051/periphery.git
cd periphery
dotnet build

Packages are published to nuget.org:

dotnet add package Periphery

Repository Layout

periphery/
├── Periphery.slnx                  # Solution — 28 src, 21 test, 7 example, 1 benchmark project
├── src/
│   ├── Periphery/                  # Core: enumeration, watching, tracking (net8.0;net10.0)
│   ├── Periphery.Camera[.Avalonia|.OpenCvSharp|.Testing]/
│   ├── Periphery.Hid/  Periphery.Monitor/  Periphery.Usb/
│   ├── Periphery.Treehopper[.Control|.Firmware|.Flasher|.Libraries][.Cli|.Gui]/
│   ├── Periphery.Firmware/  Periphery.Bootloader[.Efm8.Usb|.Stm32.Usb]/
│   ├── Periphery.FlashAnything[.Cli|.Gui][.Core]/
│   └── Periphery.Cli/  Periphery.Diagnostics/
├── tests/                          # One test project per src package, plus
│                                   #   *.Interop.Tests where a suite needs a
│                                   #   native payload (Category=Integration)
├── examples/                       # Runnable samples + single-file `dotnet run` scripts
├── benchmarks/                     # BenchmarkDotNet suites
└── docs/
    ├── ARCHITECTURE.md             # Detailed architecture & design decisions
    ├── adr/                        # Architecture Decision Records
    ├── patterns/                   # Cross-cutting conventions
    ├── surface/                    # Consumer-facing usage guides
    ├── plans/  feature-specs/      # Point-in-time design work
    └── explorations/  investigations/

Inside the core library:

src/Periphery/
├── Devices.cs                      # Static entry point: Enumerate(), Watch()
├── DeviceQuery.cs                  # Fluent, composable query (IAsyncEnumerable)
├── DeviceWatcher.cs                # Real-time Appeared/Activated/Deactivated/Disappeared monitor
├── DeviceTracker.cs                # Per-device observable state handle
├── MultiDeviceTracker.cs           # Observable set of matching devices
├── DeviceSessionHost.cs            # Session publication over a reconnecting handle
├── DeviceProxy[Base].cs            # Reconnect-resilient device handles (ADR-0027)
├── DeviceProfile.cs                # Named candidate in a multi-profile tracker
├── DeviceInfo.cs                   # Immutable device snapshot record
├── DeviceCategory.cs  DeviceTags.cs
├── DeviceFilter.cs                 # Filter predicate composition — the one source of truth
├── IDeviceProvider.cs              # Provider interfaces + runtime factory
├── *Enricher.cs                    # Tag-emitting enrichers (ADR-0026, ADR-0051)
├── DeviceReset.cs  Reset*.cs  *RecoveryPolicy.cs   # Reset/recovery escalation (ADR-0060)
├── Windows/                        # SetupAPI + cfgmgr32 + DisplayConfig
├── Linux/                          # libudev
├── MacOS/                          # IOKit / CoreFoundation
└── Serialization/                  # System.Text.Json converters for the BCL-typed fields

Design Principles

1. Discovery in the core, interaction in extensions. The core tells you what's connected; protocol-level communication (camera capture, HID reports, raw USB, DDC/CI, …) lives in companion extension libraries layered on the core's device model.
2. Platform parity. Every device category exposed in the public API must be supportable on all target platforms, even if implementations ship incrementally.
3. LINQ-native. Device queries compose naturally with Where, Select, OrderBy, and friends.
4. No third-party dependencies in the core or the I/O extensions. Platform back-ends use only built-in OS APIs (SetupAPI/cfgmgr32, udev, IOKit) via P/Invoke or native interop. Microsoft.Extensions.Logging.Abstractions is the one exception. An opt-in integration package is where a third-party dependency belongs: Periphery.Camera.Avalonia references Avalonia and Periphery.Camera.OpenCvSharp references OpenCvSharp4, and you take either package only if you want it. See docs/patterns/integration-package-placement.md.
5. Async-first. Hardware enumeration can be slow; all public entry points return Task or IAsyncEnumerable.

Contributing

Contributions are welcome. Start with CONTRIBUTING.md for how to build, test and format, and ARCHITECTURE.md for a deeper look at the design before opening a PR.

Security reports go through SECURITY.md, not the issue tracker.

Deferred work, bugs and design questions are tracked as GitHub issues — that is the only backlog. Architectural decisions live in docs/adr/; an issue that needs one references it by number.

Formatting

Formatting is CSharpier, pinned as a local tool so everyone runs the same version:

dotnet tool restore
dotnet csharpier format .

.csharpierrc sets endOfLine: lf to match .gitattributes; everything else is CSharpier's default.

The existing tree is not formatted yet. CSharpier would currently rewrite most of it, so a repo-wide pass is a deliberate change of its own rather than something to fold into an unrelated PR. Until that happens, format the files you touch and leave the rest alone.

License

PolyForm Small Business 1.0.0 - see LICENSE.md.

Source-available, not open source. Every right the licence grants - including making changes and redistributing - is granted only for a permitted purpose, and use for the benefit of a company is a permitted purpose only below the employee-count and revenue thresholds the licence sets.

LICENSE.md is the authoritative statement of the terms. This paragraph points at it and is not a summary of it.