A high-performance, asynchronous USB Host driver implementation written in Rust for embedded systems and operating system kernels.

• 🔄 Async/Await Support: Built from the ground up with async primitives for non-blocking USB operations
• ⚡ Lock-Free Design: Ring-based architecture using TRB (Transfer Request Block) for zero-lock async operations
• 🎯 xHCI Controller Support: Complete implementation of the xHCI (Extensible Host Controller Interface) specification
• 📱 USB Standards Compliance: Full support for USB 1.1, 2.0, and 3.x devices (Full, High, and SuperSpeed)
• 🔧 No-STD Compatible: Designed for #![no_std] environments with minimal memory footprint
• 🖥️ User-Space libusb Backend: Optional libusb backend for testing and development in user-space environments

• Control Transfers: Device setup, configuration, and standard requests
• Bulk Transfers: High-throughput data transfer for storage devices
• Interrupt Transfers: Periodic data transfer for HID devices
• Isochronous Transfers: Real-time streaming for audio/video devices

• 🔍 Device Enumeration: Automatic discovery and enumeration of connected USB devices
• 📋 Descriptor Parsing: Complete parsing of device, configuration, interface, and endpoint descriptors
• 🔌 Interface Management: Easy interface claiming and endpoint access
• 🏷️ String Descriptors: Full support for manufacturer, product, and serial number strings

• Executor Agnostic: Works with any async executor or can be used synchronously
• DMA-Aware: Efficient memory management with DMA coherency support
• Event-Driven: Interrupt-based event handling for optimal performance
• Modular Design: Clean separation between host controller and USB interface layers
• Multi-Backend Support: Supports both direct hardware access (xHCI) and user-space testing (libusb)

CrabUSB uses an innovative lock-free design based on TRB rings where each TRB represents an async task. The future queries the ring to obtain async results without requiring a specific executor, making it highly flexible and performant.

The driver supports multiple backends:

• xHCI Backend: Direct hardware access for embedded systems and OS kernels
• libusb Backend: User-space testing and development using libusb (enable with libusb feature)

┌─────────────────┐    ┌──────────────────┐    ┌─────────────────┐
│   Application   │◄──►│   USB Interface  │◄──►│    Backend      │
│                 │    │     (usb-if)     │    │   Selection     │
└─────────────────┘    └──────────────────┘    └─────────────────┘
                              │                          │
                              ▼                          ▼
                       ┌──────────────┐         ┌──────────────┐
                       │ Descriptors  │         │ xHCI / libusb│
                       │ & Transfers  │         │   Drivers    │
                       └──────────────┘         └──────────────┘