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usb-stack

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USB device and host stack implementation expertise

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How to use this skill

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Source SKILL.md: https://github.com/a5c-ai/babysitter/blob/HEAD/library/specializations/embedded-systems/skills/usb-stack/SKILL.md

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USB Stack Skill

Overview

This skill provides USB device and host stack implementation expertise for embedded systems, covering descriptor generation, device class implementation, and protocol debugging.

Capabilities

USB Descriptor Generation

  • Device descriptor configuration
  • Configuration descriptors
  • Interface descriptors
  • Endpoint descriptors
  • String descriptors
  • BOS descriptors (USB 3.x)

Device Class Implementation

  • CDC (Communications Device Class)
  • HID (Human Interface Device)
  • MSC (Mass Storage Class)
  • DFU (Device Firmware Upgrade)
  • Audio class
  • Video class
  • Custom class implementation

USB Stack Configuration

  • TinyUSB configuration
  • STM32 USB stack setup
  • NXP USB stack integration
  • Zephyr USB subsystem
  • Endpoint buffer management

Enumeration and Debugging

  • Enumeration sequence debugging
  • Protocol analysis
  • USB analyzer integration
  • Descriptor validation
  • Compliance testing

Advanced Features

  • Composite device configuration
  • USB power delivery
  • High-speed/full-speed selection
  • Isochronous transfers
  • Interrupt transfers
  • Bulk transfers

DFU Implementation

  • DFU bootloader design
  • Runtime DFU mode
  • Detach and download
  • Upload capability
  • Manifest phase handling

Target Processes

  • device-driver-development.js - USB driver implementation
  • bootloader-implementation.js - USB DFU bootloader
  • hw-sw-interface-specification.js - USB interface specification

Dependencies

  • TinyUSB or vendor USB stack
  • USB protocol analyzers
  • usb-tools (lsusb, usbmon)

Usage Context

This skill is invoked when tasks require:

  • USB device implementation
  • Device class development
  • USB bootloader creation
  • Protocol debugging
  • Descriptor optimization

Device Class Examples

CDC Virtual COM Port

tusb_desc_interface_t cdc_interface = {
    .bLength            = sizeof(tusb_desc_interface_t),
    .bDescriptorType    = TUSB_DESC_INTERFACE,
    .bInterfaceNumber   = 0,
    .bAlternateSetting  = 0,
    .bNumEndpoints      = 2,
    .bInterfaceClass    = TUSB_CLASS_CDC,
    .bInterfaceSubClass = CDC_COMM_SUBCLASS_ACM,
    .bInterfaceProtocol = CDC_COMM_PROTOCOL_NONE,
    .iInterface         = 0
};

HID Report Descriptor

uint8_t const hid_report_desc[] = {
    HID_USAGE_PAGE(HID_USAGE_PAGE_DESKTOP),
    HID_USAGE(HID_USAGE_DESKTOP_MOUSE),
    HID_COLLECTION(HID_COLLECTION_APPLICATION),
        HID_USAGE(HID_USAGE_DESKTOP_POINTER),
        HID_COLLECTION(HID_COLLECTION_PHYSICAL),
            // ... buttons and axes
        HID_COLLECTION_END,
    HID_COLLECTION_END
};

Configuration

usb:
  vid: 0x1234
  pid: 0x5678
  device_class: cdc | hid | msc | dfu | composite
  speed: full | high
  endpoints:
    - ep1_in: bulk, 64
    - ep1_out: bulk, 64