Added purpose and description.

libraries/io/ddr/src/vhdl/io_ddr_driver.vhd

@@ -20,6 +20,12 @@
 --
 --------------------------------------------------------------------------------
 
+-- Purpose: Provide streaming interface to DDR memory
+-- Description:
+--   Write or read a block of data to or from DDR memory. The block of data is
+--   located from dvr_start_addr to dvr_end_addr. The io_ddr_driver takes care
+--   that the access is done in a number of bursts.
+
 LIBRARY IEEE, tech_ddr_lib, common_lib, dp_lib;
 USE IEEE.STD_LOGIC_1164.ALL;
 USE IEEE.NUMERIC_STD.ALL;