USB_DEVICE_QUALIFIER_DESCRIPTOR 详解

USB_DEVICE_QUALIFIER_DESCRIPTOR structure

The USB_DEVICE_QUALIFIER_DESCRIPTOR structure is used by USB client drivers to retrieve a USB-defined device qualifier descriptor.

Syntax

typedef struct _USB_DEVICE_QUALIFIER_DESCRIPTOR {
  UCHAR  bLength;
  UCHAR  bDescriptorType;
  USHORT bcdUSB;
  UCHAR  bDeviceClass;
  UCHAR  bDeviceSubClass;
  UCHAR  bDeviceProtocol;
  UCHAR  bMaxPacketSize0;
  UCHAR  bNumConfigurations;
  UCHAR  bReserved;
} USB_DEVICE_QUALIFIER_DESCRIPTOR, *PUSB_DEVICE_QUALIFIER_DESCRIPTOR;

Members

bLength

Specifies the length, in bytes, of this descriptor.

bDescriptorType

Specifies the descriptor type. Must be set to USB_DEVICE_QUALIFIER_DESCRIPTOR_TYPE.

bcdUSB

Identifies the version of the USB specification that this descriptor structure complies with. This value is a binary-coded decimal number.

bDeviceClass

Specifies the class code of the device as assigned by the USB specification group.

bDeviceSubClass

Specifies the subclass code of the device as assigned by the USB specification group.

bDeviceProtocol

Specifies the protocol code of the device as assigned by the USB specification group.

bMaxPacketSize0

Specifies the maximum packet size, in bytes, for endpoint zero of the device. The value must be set to 8, 16, 32, or 64.

bNumConfigurations

Specifies the total number of possible configurations for the device.

bReserved

Reserved.

Remarks

This structure is similar to , but it contains only those members that can change when the device switches from full-speed operation to high-speed operation or vice versa. If the device is operating at full speed, querying for this descriptor will contain information about how the device would operate at high-speed. If, on the other hand, the device is operating at high-speed, this descriptor will contain information about how the device would operate at full-speed.

Requirements

Header	Usb200.h (include Usb200.h)

See also

 

 

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