再问一个问题!

就是<<Windows WDM 设备驱动开指南>>中代人例子USBKBD
为什么不能读到HID 描述符呢，我跟踪发现是 驱动有问题，
返的数据的长度为零，其原码如下：
NTSTATUS UsbGetSpecifiedDescriptor( IN PUSBKBD_DEVICE_EXTENSION dx,
OUT PVOID& Descriptor,
IN UCHAR DescriptorType,
IN OUT ULONG& Size)
{
// Allocate memory for URB
USHORT UrbSize = sizeof(struct _URB_CONTROL_DESCRIPTOR_REQUEST);
PURB urb = (PURB)ExAllocatePool(NonPagedPool, UrbSize);
if( urb==NULL)
{
DebugPrintMsg(\"No URB memory\");
return STATUS_INSUFFICIENT_RESOURCES;
}

// Allocate memory for descriptor
Descriptor = ExAllocatePool(NonPagedPool, Size);
if( Descriptor==NULL)
{
ExFreePool(urb);
DebugPrintMsg(\"No descriptor memory\");
return STATUS_INSUFFICIENT_RESOURCES;
}

// Build the Get Descriptor URB
UsbBuildGetDescriptorRequest(
urb, UrbSize,
DescriptorType, 0, 0, // Types, Index & LanguageId
Descriptor, NULL, Size, // Transfer buffer
NULL); // Link URB

// Call the USB driver
DebugPrint(\"Getting descriptor type %2x\", DescriptorType);
NTSTATUS status = CallUSBDI( dx, urb);
// Check statuses
if( !NT_SUCCESS(status) || !USBD_SUCCESS( urb->UrbHeader.Status))
{
DebugPrint(\"status %x URB status %x\", status, urb->UrbHeader.Status);
status = STATUS_UNSUCCESSFUL;
}
Size = urb->UrbControlDescriptorRequest.TransferBufferLength;

ExFreePool(urb);
return status;
}

问题找个了，是和USB的版本有关，测试程序的没有正确发送给驱动数据的长度，
// Get HID Report descriptor
// Size of HID report is usually in second last byte of  
//above descriptors
将  ULONG Size = descriptors[BytesReturned-2];
改为ULONG Size = descriptors[BytesReturned-9];
可以了.这是在2000下运行的，在98下不要改!
谢谢ydyuse的回答!

我原来测试好象无问题，测试时你有USB键盘吗？