Added comment that host must first write low then this high part of 64-bit BSN.

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

@@ -109,7 +109,7 @@ BEGIN
             mm_scheduled_bsn(31 DOWNTO  0) <= sla_in.wrdata(31 DOWNTO 0);
           WHEN 1 =>
             mm_scheduled_bsn(63 DOWNTO 32) <= sla_in.wrdata(31 DOWNTO 0);
-            mm_scheduled_bsn_wr <= '1';
+            mm_scheduled_bsn_wr <= '1';   -- host must first write low then this high part
           
           WHEN OTHERS => NULL;  -- not used MM addresses
         END CASE;