Subversion Repositories astron_requantizer

-------------------------------------------------------------------------------
--
-- Copyright 2020
-- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>
-- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands
-- 
-- Licensed under the Apache License, Version 2.0 (the "License");
-- you may not use this file except in compliance with the License.
-- You may obtain a copy of the License at
-- 
--     http://www.apache.org/licenses/LICENSE-2.0
-- 
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS,
-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-- See the License for the specific language governing permissions and
-- limitations under the License.
--
-------------------------------------------------------------------------------
 
LIBRARY ieee, common_pkg_lib, common_components_lib;
USE ieee.std_logic_1164.ALL;
USE ieee.numeric_std.ALL;
USE common_pkg_lib.common_pkg.ALL;
 
ENTITY common_round IS
 
  --
  -- ISE XST results for rounding 36b --> 18b:
  --    int      clip  -->  slices  FFs  LUTs
  -- 1) signed   TRUE       63      54   80       -- increases with input widths > 18b
  -- 2) signed   FALSE      59      54   73       -- increases with input widths > 18b
  -- 3) unsigned TRUE       34      37   43       -- same for all input widths > 18b
  -- 4) unsigned FALSE      21      37   19       -- same for all input widths > 18b
  --
  -- If the input comes from a product and is rounded to the input width then g_round_clip can safely be FALSE, because e.g. for unsigned
  -- 4b*4b=8b->4b the maximum product is 15*15=225 <= 255-8, so wrapping will never occur.
  -- 
 
  GENERIC (
    g_representation  : STRING  := "SIGNED";  -- SIGNED (round +-0.5 away from zero to +- infinity) or UNSIGNED rounding (round 0.5 up to + inifinity)
    g_round           : BOOLEAN := TRUE;      -- when TRUE round the input, else truncate the input
    g_round_clip      : BOOLEAN := FALSE;     -- when TRUE clip rounded input >= +max to avoid wrapping to output -min (signed) or 0 (unsigned)
    g_pipeline_input  : NATURAL := 0;         -- >= 0
    g_pipeline_output : NATURAL := 1;         -- >= 0, use g_pipeline_input=0 and g_pipeline_output=0 for combinatorial output
    g_in_dat_w        : NATURAL := 36;
    g_out_dat_w       : NATURAL := 18
  );
  PORT (
    clk        : IN  STD_LOGIC;
    clken      : IN  STD_LOGIC := '1';
    in_dat     : IN  STD_LOGIC_VECTOR(g_in_dat_w-1 DOWNTO 0);
    out_dat    : OUT STD_LOGIC_VECTOR(g_out_dat_w-1 DOWNTO 0)
  );
END;
 
 
ARCHITECTURE rtl OF common_round IS
 
  CONSTANT c_remove_w     : INTEGER := g_in_dat_w-g_out_dat_w;
 
  SIGNAL reg_dat       : STD_LOGIC_VECTOR(in_dat'RANGE);
  SIGNAL res_dat       : STD_LOGIC_VECTOR(out_dat'RANGE);
 
BEGIN
 
  u_input_pipe : ENTITY common_components_lib.common_pipeline
  GENERIC MAP (
    g_representation => g_representation,
    g_pipeline       => g_pipeline_input,
    g_in_dat_w       => g_in_dat_w,
    g_out_dat_w      => g_in_dat_w
  )
  PORT MAP (
    clk     => clk,
    clken   => clken,
    in_dat  => in_dat,
    out_dat => reg_dat
  );
 
  -- Increase to out_dat width
  no_s : IF c_remove_w<=0 AND g_representation="SIGNED" GENERATE
    res_dat <= RESIZE_SVEC(reg_dat, g_out_dat_w);
  END GENERATE;
  no_u : IF c_remove_w<=0 AND g_representation="UNSIGNED" GENERATE
    res_dat <= RESIZE_UVEC(reg_dat, g_out_dat_w);
  END GENERATE;
 
  -- Decrease to out_dat width by c_remove_w number of LSbits
  -- . rounding
  gen_s : IF c_remove_w>0 AND g_round=TRUE AND g_representation="SIGNED" GENERATE
    res_dat <= s_round(reg_dat, c_remove_w, g_round_clip);
  END GENERATE;
  gen_u : IF c_remove_w>0 AND g_round=TRUE AND g_representation="UNSIGNED" GENERATE
    res_dat <= u_round(reg_dat, c_remove_w, g_round_clip);
  END GENERATE;
  -- . truncating
  gen_t : IF c_remove_w>0 AND g_round=FALSE GENERATE
    res_dat <= truncate(reg_dat, c_remove_w);
  END GENERATE;
 
  u_output_pipe : ENTITY common_components_lib.common_pipeline
  GENERIC MAP (
    g_representation => g_representation,
    g_pipeline       => g_pipeline_output,
    g_in_dat_w       => g_out_dat_w,
    g_out_dat_w      => g_out_dat_w
  )
  PORT MAP (
    clk     => clk,
    clken   => clken,
    in_dat  => res_dat,
    out_dat => out_dat
  );
 
END rtl;