Added description of tasks of the SDP OPC-UA server.

applications/lofar2/doc/prestudy/station2_opc_ua.txt

@@ -76,3 +76,16 @@ Needed:
 
 
 
+The tasks of the SDP OPC-UA server are:
+
+* Translate between OPC-UA interface at Station Control side and Gemini protocol over UDP/IP at
+  UniBoard2 side
+* Obtain the named register map of the FPGA firmware from a definition in YAML (the schema for
+  the description in YAML is defined in ARGS = automatic register generation system).
+* Present the registers per FPGA for the array of FPGAs as data points in OPC-UA. This could be
+  generated automatically based on the regmap description in YAML for each FPGA
+* Present registers that are distributed over an array of FPGAs as a single array of data points
+  in OPC-UA (e.g. for beamformer weights, crosslet statistics). This abstracts away the notion
+  of which FPGA takes care of which signal inputs, instead all signal inputs are represented as 
+  a single array. This is probably a manually written software layer / add-on in the SDP
+  OPC-CU server.