Overview

This chapter describes how to write a USB driver that uses the Windows USB Driver Interface (USBDI). The UsbKbd example driver talks to a USB keyboard and retrieves the raw keyboard input data. The corresponding Win32 test application displays this input data. In addition, you finally get the opportunity to flash some LEDs (the LEDs on keyboard).

A USB client is a device driver that uses the standard Windows system USB class drivers to talk to USB devices using USBDI. USBD.sys is the USB class driver. It uses either UHCD.sys to talk to Universal Host Controller Interface devices, or OpenHCI.sys for Open Host Controller Interface devices. USBHUB.sys is the USB driver for root hubs and external hubs. The relevant drivers are loaded when the PCI Enumerator finds each USB host controller.

Windows 2000 runs USBDI version 2.00, while Windows 98 uses version 1.01. There is no documentation on the differences. USBDI version 2.0 might return some Windows Management Instrumentation (WMI) data. Use the USBD_GetUSBDIVersion function to determine what version of the USB class drivers you are using. Only one very minor aspect of this chapter's driver is affected by the USBDI version.

As far as a USB client driver is concerned, the host computer (the Windows PC) talks directly to any function device that is plugged in. The details of bus enumeration and how information is transferred are not directly of concern to a USB client.

However, a client does need to be...