USB Host Driver

The Universal Serial Bus (USB) is an industry standard that defines the cables, connectors, and communication protocols used in a bus for connection, communication, and power supply between computers and electronic devices.

The USB host driver provides necessary APIs to support USB states and USB data flow. So that the USB Device enumeration, class and vendor support can be implemented base on it. The driver is asynchronous, which means that all USB data processing is done in callbacks.

To recognized a device, a USB host must handle a subset of the USB events. The USB host should turn on VBus supply, monitor root hub events, build up control communication to request descriptors of attached device. An application or upper stack that uses the USB host driver should have its descriptors buffer prepared, issue the control requests, analyze the returned descriptors and handle them correctly.

Usually, a USB host application that can enumerates USB device may use the following sequence:

  • Initialize

  • Register callback and handle root hub events, where:

    • On connection, issue USB Reset

    • On USB Reset end, initialize pipe 0, register request end callback and issue *GetDeviceDescriptor- request

    • On disconnection, free all allocated pipes

  • In pipe 0 request done handling callback:

    • On *GetDeviceDescriptor- OK, modify pipe 0 endpoint size according to the descriptor returned, issue *SetAddress- request

    • On *SetAddress- request OK, issue *GetConfigurationDescriptor- request

    • On *GetConfigurationDescriptor- request OK, create pipes based on returned configuration descriptor; issue *SetConfigure- request

  • Enable

  • After the *SetConfigure- request is done correctly, the created pipes should be OK to communicate with the USB device

Parent topic: USB Drivers

Summary of the API's Functional Features

The API provides functions to:

  • Initialization/de-initialization

  • Enabling/disabling

  • USB root hub control

    • Attach/detach detection

    • Reset

    • Suspend/resume

    • Connection speed detection

  • USB host frame number and micro frame number status

  • Callback management for:

    • Start of Frame (SOF)

    • Root hub events

  • Pipes management:

    • Pipe allocation/free

    • Control pipe request

    • Bulk, interrupt and ISO pipe transfer

    • Pipe callback management for transfer done

Dependencies

  • The USB host capable hardware

  • 48MHz clock for low-speed and full-speed and 480MHz clock for high-speed