求教：USB bulk 传输的问题。

从应用程序调用驱动程序里的输入输出dispatch例程，输入输出是通过自定义IOCTL控制代码实现的！但在程序运行中发现，把相应的URB发送到 bus driver 后一直等待，而不返回。


//the following one routine is to
// forward a urb to usb bus driver.

NTSTATUS
Evk_CallUSBD(IN PDEVICE_OBJECT   fdo,
IN PURB             urb)
{
NTSTATUS  ntStatus,status=STATUS_SUCCESS;

PDEVICE_EXTENSION       pdx;

PIRP                    irp;
IO_STATUS_BLOCK         ioStatus;
    PIO_STACK_LOCATION      nextStack;

KEVENT                  event;

Evk_KdPrint((\"enter Evk_CallUSBD()\\n\"));

pdx=fdo->DeviceExtension;

//issue a synchronous request
KeInitializeEvent(&event,NotificationEvent,FALSE);
    
//build irp which will be send to bus driver
irp=IoBuildDeviceIoControlRequest(IOCTL_INTERNAL_USB_SUBMIT_URB,
                             pdx->LowerDeviceObject,
 NULL,
 0,
 NULL,
 0,
 TRUE,   //internal
 &event,
 &ioStatus);
//prepare for calling the usb bus driver
    nextStack=IoGetNextIrpStackLocation(irp);
    ASSERT(nextStack!=NULL);

    nextStack->Parameters.Others.Argument1=urb;

Evk_KdPrint((\"Calling USB driver stack\"));

//call the USB driver stack to perform the operation.if the return value is
//PENDING ,wait for request to complete

ntStatus=IoCallDriver(pdx->LowerDeviceObject,irp);

Evk_KdPrint ((\"return from IoCallDriver USBD %x\\n\", ntStatus));
    
//STATUS_PENDING means the lower driver have not finished processing the IRP,
//yet.we must wait.
if(ntStatus==STATUS_PENDING)
{
Evk_KdPrint ((\"Wait for single object\\n\"));
status=KeWaitForSingleObject(
                        &event,
Suspended,
KernelMode,
FALSE,
NULL);
Evk_KdPrint ((\"Wait for single object, returned %x\\n\", status));
}
else
{
ioStatus.Status=ntStatus;
}

    Evk_KdPrint ((\"URB status = %x status = %x irp status %x\\n\",
     urb->UrbHeader.Status, status, ioStatus.Status));


  //USBD maps the error code for us,USBD uses error codes in its URB structure,
  //that are more insightful into USB behavior.in order to match the
  //NT status code,USBD maps its error codes into more general NT
   // error categories so higher level drivers can decipher the error codes
   // based on standard NT error code definitions.
   //

ntStatus=ioStatus.Status;
//
   // If the URB status was not USBD_STATUS_SUCCESS, we save a copy of the
   // URB status in the device extension.  After a failure, another IOCTL,
   // IOCTL_EVK_GET_LAST_ERROR can be used to retrieve the URB status
   // for the most recently failed URB.  Of course, this status gets
   // overwritten by subsequent failures, but it\'s better than nothing.
   //
if(NT_SUCCESS(ntStatus))
{
 if(!USBD_SUCCESS(urb->UrbHeader.Status))
ntStatus=STATUS_UNSUCCESSFUL;
}

Evk_KdPrint((\"exit Evk_CallUSBD (%x)\\n\", ntStatus));

   return ntStatus;
}


也就是说 IoCallDriver 的返回值是STATUS_PENDING 从而执行 status=KeWaitForSingleObject(....);
当它一直完成不了。

高手们认为是什么原因呢？