Added note on circular buffer for bsn aligner v2.

applications/lofar2/doc/prestudy/station2_sdp_hdl_components.txt

@@ -329,7 +329,16 @@ Design options:
   ==> Design decision:
       Do not make or use a dp_sync_aligner, because loosing an entire sync interval is not acceptable.
       
-      
+. Assume circular buffer:
+  - advantage:
+    . direct access to each word in block
+    . no need to flush blocks, status bit per block tells whether it is filled
+  - buffer is filled and read after certain latency, because then all remote packets should have arrived
+    . provide CP for active input streams, is this needed ?
+  - use MM interface to read from head column (with block for all parallel streams)
+  - provide mm to dp component with bsn aligner (= dp_block_from_mm ?)
+  - provide MP for nof lost = nof filler blocks / stream ?
+    . err at eop indicates lost = filler data, sosi_info could have eop at sop like with crosslets_info
       
 . Initial alignment:
   - Assume the received packets on the inputs contain one block per packet.