URB
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_URB_CONTROL_TRANSFER structure

The _URB_CONTROL_TRANSFER structure is used by USB client drivers to transfer data to or from a control pipe.

Syntax


struct _URB_CONTROL_TRANSFER {
  struct URB_HEADER  Hdr;
  USBD_PIPE_HANDLE    PipeHandle;
  ULONG               TransferFlags;
  ULONG               TransferBufferLength;
  PVOID               TransferBuffer;
  PMDL                TransferBufferMDL;
  struct URB  *UrbLink;
  struct URB_HCD_AREA  hca;
  UCHAR               SetupPacket[8];
};

Members

Hdr

Pointer to a _URB_HEADER structure that specifies the URB header information. Hdr.Function must be URB_FUNCTION_CONTROL_TRANSFER, and Hdr.Length must be sizeof(_URB_CONTROL_TRANSFER).

PipeHandle

Handle for the control pipe.

If target is the default control endpoint, then PipeHandle must be NULL. In this case, the TransferFlags must contain the USBD_DEFAULT_PIPE_TRANSFER flag.

If target is a non-default control endpoint, PipeHandle specifies an opaque handle for the control pipe. The host controller driver returns this handle when the client driver selects the device configuration with a URB of type URB_FUNCTION_SELECT_CONFIGURATION or when the client driver changes the settings for an interface with a URB of type URB_FUNCTION_SELECT_INTERFACE.

TransferFlags

Specifies zero, one, or a combination of the following flags:

ValueMeaning
USBD_TRANSFER_DIRECTION_IN

Is set to request data from a device. To transfer data to a device, this flag must be clear.

USBD_TRANSFER_DIRECTION_OUT

Is set to transfer data to a device. Setting this flag is equivalent to clearing the USBD_TRANSFER_DIRECTION_IN flag.

USBD_SHORT_TRANSFER_OK

Is set to direct the host controller not to return an error when it receives a packet from the device that is shorter than the maximum packet size for the endpoint. The maximum packet size for the endpoint is reported in the bMaxPacketSize0 member of the USB_DEVICE_DESCRIPTOR structure (device descriptor) for the default control endpoint. For a non-default control endpoint, maximum packet size is set in the wMaxPacketSize member of the USB_ENDPOINT_DESCRIPTOR structure (endpoint descriptor).

When the host controller receives a packet whose length is shorter than the wMaxPacketSize value on a control endpoint, the behavior is as follows depending on the type of host controller:

  • On EHCI host controllers, the host controller proceeds immediately to the status phase of the control transfer. The transfer completes successfully, regardless of whether USBD_SHORT_TRANSFER_OK is set.
  • On UHCI and OHCI host controllers, if USBD_SHORT_TRANSFER_OK is set, the host controller proceeds to the status phase. If USBD_SHORT_TRANSFER_OK is not set, the host controller abandons the data and status phases of the control transfer and the transfer completes with an error.
USBD_DEFAULT_PIPE_TRANSFER

Is set to direct the host controller to do a control transfer on the default control pipe. This allows the caller to send commands to the default control pipe without explicitly specifying the pipe handle.

 

TransferBufferLength

Specifies the length, in bytes, of the buffer specified in TransferBuffer or described in TransferBufferMDL. The host controller driver returns the number of bytes sent to or read from the pipe in this member.

TransferBuffer

Pointer to a resident buffer for the transfer or is NULL if an MDL is supplied in TransferBufferMDL. The contents of this buffer depend on the value of TransferFlags. If USBD_TRANSFER_DIRECTION_IN is specified this buffer will contain data read from the device on return from the host controller driver. Otherwise, this buffer contains driver-supplied data for transfer to the device.

TransferBufferMDL

Pointer to an MDL that describes a resident buffer or is NULL if a buffer is supplied in TransferBuffer. The contents of the buffer depend on the value of TransferFlags. If USBD_TRANSFER_DIRECTION_IN is specified, the described buffer will contain data read from the device on return from the host controller driver. Otherwise, the buffer contains driver-supplied data for transfer to the device. This MDL must be allocated from nonpaged pool.

UrbLink

Reserved. Do not use.

hca

Reserved. Do not use.

SetupPacket

Specifies a USB-defined request setup packet. The format of a USB request setup packet is found in the USB core specification.

Remarks

The URB_CONTROL_TRANSFER_EX structure is identical to URB_CONTROL_TRANSFER, except that it provides a timeout value in the Timeout field.

The reserved members of this structure must be treated as opaque and are reserved for system use.

Requirements

Header

Usb.h (include Usb.h)

See also

URB
URB_CONTROL_TRANSFER_EX
_URB_HEADER
USB Structures

 

 

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