This module links the host chip to the target chip via SERDES line. It assures half-duplex communication for compilation and loading of an application as well as for development utilities.
This node receives requests via ether messages sent to its DOWN port or directly from node 700. There are two kinds of requests. The node may be instructed to build SERDES link to the target node upon reset, in which case it receives a special ether message followed by compiled SERDES slave code; or it receives a standard ether message that contains a link, i.e. a path within the target chip, in the first word of payload as is explained in Ether section of system description.
As an ether message may request some reply from the target node, code in node 701 can automatically turn it into SERDES slave when needed, deliver the reply to the source of the ether message, and turn the node back to SERDES master.
When receiving requests from node 700, node 701 has to be deceived to believe it's an ether message what is delivered to its RIGHT port. For that reason node 700 starts communication with a fake ether header although it has a direct access to the port.