Updated comment.

libraries/base/dp/src/vhdl/dp_bsn_sync_scheduler.vhd

@@ -18,7 +18,8 @@
 --
 -- Author: Eric Kooistra, 30 July 2021
 -- Purpose : 
---   Create programmable sync interval for input stream.
+--   Create programmable sync interval for input stream, according to the
+--   PPS and BSN grid defined in [1].
 -- Description:
 -- * ctrl_start_bsn:
 --   The output sync interval starts at an in_sosi.bsn that is programmable via
@@ -105,6 +106,9 @@
 --   The differences are that:
 --   . dp_bsn_sync_scheduler requires in_sosi.sync and copies the other in_sosi
 --     ctrl, info and data, whereas generates bs_sosi.ctrl.
+--
+-- References:
+-- [1] https://support.astron.nl/confluence/display/L2M/L2+STAT+Decision%3A+Timing+in+Station
 
 LIBRARY IEEE, common_lib;
 USE IEEE.STD_LOGIC_1164.ALL;