c# USB parsing of a _URB_BULK_OR_INTERRUPT_TRANSFER packet

I'm parsing a _URB_BULK_OR_INTERRUPT_TRANSFER packet as defined in http://msdn.microsoft.com/en-us/library/windows/hardware/ff540352(v=vs.85).aspx using the following code:

            //parse URB Packet
            /*
            _URB_HEADER {
            USHORT      Length;
            USHORT      Function;
            USBD_STATUS Status;
            PVOID       UsbdDeviceHandle;
            ULONG       UsbdFlags;
            }*/

            //start header parse
            UInt16 urb_length = rdr.ReadUInt16();
            UInt16 urb_function = rdr.ReadUInt16();
            UInt32 urb_status = rdr.ReadUInt32();
            rdr.ReadBytes(System.IntPtr.Size);
            UInt32 UsbdFlags = rdr.ReadUInt32();
            //end header parse

            //.. skip code to check if it a _URB_BULK_OR_INTERRUPT_TRANSFER 
            // but assuming it is parse it

            /*struct _URB_BULK_OR_INTERRUPT_TRANSFER {
            struct URB_HEADER  Hdr;//covered above
            USBD_PIPE_HANDLE    PipeHandle;
            ULONG               TransferFlags;
            ULONG               TransferBufferLength;
            PVOID               TransferBuffer;
            PMDL                TransferBufferMDL;
            struct URB  *UrbLink;
            struct URB_HCD_AREA  hca;
            }*/

            rdr.ReadBytes(System.IntPtr.Size);
            UInt32 TransferFlags = rdr.ReadUInt32();
            UInt32 TransferBufferLength = rdr.ReadUInt32();
            byte[] ptr_bytes = rdr.ReadBytes(System.IntPtr.Size);
            System.IntPtr ptr_transfer_buffer = new System.IntPtr(BitConverter.ToUInt32(ptr_bytes, 0));
            ptr_bytes = rdr.ReadBytes(System.IntPtr.Size);
            System.IntPtr mdl_transfer_buffer = new System.IntPtr(BitConverter.ToUInt32(ptr_bytes, 0))

Inspecting all the values as 开发者_StackOverflow社区they are being read in, most seem sensible until the PMDL void pointer. This ends up being a large negative number instead of 0 (NULL) or a valid address. Can anyone point me in the right direction as to why this might be happening? Thanks.

MDL objects are memory descriptors only usable in kernel mode. Due to the user/kernel-mode split, virtual addresses over 2 GB on x86 systems (without the 3GB switch) are in the kernel virtual address space.

I don't quite understand your question... TransferBufferMDL is used in DirectIO cases whereas TransferBuffer is for Buffered IO.

So one of those two will always be void.

Hope this helps!