Automatic - Pure data streaming.  Destination MAC/IP/Port address is fixed.
  Framing is performed automatically by the core.  Frame boundary is
  when either the input fifo is empty, or the frame is too big.

Semi-automatic - Data streaming with optional eof delimiters.  Same as
  before, but there is an extra bit in the input fifo which can force
  a frame break.

Manual-breaks - Manual frame breaks. Same as before but with no
  automatic framing.  Any frame that is too big is discarded.  If the
  fifo becomes empty before the end of the frame, the frame is
  discarded.

Manual - Manual frames.  Same as before, but the MAC address and
  EthType of each frame is sent as the first words of the frame.

