IN  PDMA_ADAPTER  DmaAdapter,
  IN  PMDL  Mdl,
  IN  PVOID  MapRegisterBase,
  IN  PVOID  CurrentVa,
  IN OUT PULONG  Length,
  IN  BOOLEAN  WriteToDevice

Routine Description:

    Hooked version of MapTransfer.


    DmaAdapter -- adapter we're using to map the transfer.
    Mdl -- describes memory to map.
    MapRegisterBase -- Lets the hal monkey around with the data. I hook
        this if I am doing double buffering.
    CurrentVa -- where in the transfer we are.
    Length -- how many bytes to transfer (and how many bytes hal is going
        to let you  transfer).
    WriteToDevice -- direction of transfer.

Return Value:

    PHYSICAL_ADDRESS that is the memory to be transferred as seen by the