Subversion Repositories astron_statistics

-------------------------------------------------------------------------------

--

-- Copyright (C) 2010

-- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>

-- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands

--

-- This program is free software: you can redistribute it and/or modify

-- it under the terms of the GNU General Public License as published by

-- the Free Software Foundation, either version 3 of the License, or

-- (at your option) any later version.

--

-- This program is distributed in the hope that it will be useful,

-- but WITHOUT ANY WARRANTY; without even the implied warranty of

-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

-- GNU General Public License for more details.

--

-- You should have received a copy of the GNU General Public License

-- along with this program.  If not, see <http://www.gnu.org/licenses/>.

--

-------------------------------------------------------------------------------

LIBRARY IEEE, common_pkg_lib, common_components_lib, common_add_sub_lib;

USE IEEE.std_logic_1164.ALL;

USE IEEE.numeric_std.ALL;

USE common_pkg_lib.common_pkg.ALL;

-- Purpose:

--   Accumulate input data to an accumulator that is stored externally. In this

--   way blocks of input samples (e.g. subband products) can be accumulated to

--   a set of external accumulators. At the in_load the accumulator input value

--   is ignored so that the accumulation restarts with the in_dat.

--

-- Description:

--   if in_load = '1' then

--     out_acc = in_dat + 0         -- restart accumulation

--   else

--     out_acc = in_dat + in_acc    -- accumulate

--

-- Remarks:

-- . in_val propagates to out_val after the pipeline latency but does not 

--   affect the sum

ENTITY st_acc IS

  GENERIC (

    g_dat_w            : NATURAL;

    g_acc_w            : NATURAL;  -- g_acc_w >= g_dat_w

    g_hold_load        : BOOLEAN := TRUE;

    g_pipeline_input   : NATURAL;  -- 0 no input registers, else register input after in_load

    g_pipeline_output  : NATURAL   -- pipeline for the adder

  );

  PORT (

    clk         : IN  STD_LOGIC;

    clken       : IN  STD_LOGIC := '1';

    in_load     : IN  STD_LOGIC;

    in_dat      : IN  STD_LOGIC_VECTOR(g_dat_w-1 DOWNTO 0);

    in_acc      : IN  STD_LOGIC_VECTOR(g_acc_w-1 DOWNTO 0);

    in_val      : IN  STD_LOGIC := '1';

    out_acc     : OUT STD_LOGIC_VECTOR(g_acc_w-1 DOWNTO 0);

    out_val     : OUT STD_LOGIC

  );

END st_acc;

ARCHITECTURE rtl OF st_acc IS

  CONSTANT c_pipeline  : NATURAL := g_pipeline_input + g_pipeline_output;

  -- Input signals

  SIGNAL hld_load        : STD_LOGIC := '0';

  SIGNAL nxt_hld_load    : STD_LOGIC;

  SIGNAL acc_clr        : STD_LOGIC;

  SIGNAL reg_dat        : STD_LOGIC_VECTOR(g_acc_w-1 DOWNTO 0) := (OTHERS=>'0');

  SIGNAL nxt_reg_dat    : STD_LOGIC_VECTOR(g_acc_w-1 DOWNTO 0);

  SIGNAL reg_acc        : STD_LOGIC_VECTOR(g_acc_w-1 DOWNTO 0) := (OTHERS=>'0');

  SIGNAL nxt_reg_acc    : STD_LOGIC_VECTOR(g_acc_w-1 DOWNTO 0);

  -- Pipeline control signals, map to slv to be able to use common_pipeline

  SIGNAL in_val_slv     : STD_LOGIC_VECTOR(0 DOWNTO 0);

  SIGNAL out_val_slv    : STD_LOGIC_VECTOR(0 DOWNTO 0);

BEGIN

  ASSERT NOT(g_acc_w < g_dat_w)

    REPORT "st_acc: output accumulator width must be >= input data width"

    SEVERITY FAILURE;

  ------------------------------------------------------------------------------

  -- Input load control

  ------------------------------------------------------------------------------

  p_clk : PROCESS(clk)

  BEGIN

    IF rising_edge(clk) THEN

      IF clken='1' THEN

        hld_load <= nxt_hld_load;

      END IF;

    END IF;

  END PROCESS;

  nxt_hld_load <= in_load WHEN in_val='1' ELSE hld_load;

  -- Hold in_load to save power by avoiding unneccessary out_acc toggling when in_val goes low  

  -- . For g_pipeline_input>0 this is fine

  -- . For g_pipeline_input=0 this may cause difficulty in achieving timing closure for synthesis

  use_in_load : IF g_hold_load = FALSE GENERATE

    acc_clr <= in_load;  -- the in_load may already be extended during in_val

  END GENERATE;

  use_hld_load : IF g_hold_load = TRUE GENERATE

    acc_clr <= in_load OR (hld_load AND NOT in_val);

  END GENERATE;

  -- Do not use g_pipeline_input of u_adder, to allow registered acc clear if g_pipeline_input=1

  nxt_reg_dat <= RESIZE_SVEC(in_dat, g_acc_w);

  nxt_reg_acc <= in_acc WHEN acc_clr='0' ELSE (OTHERS=>'0');

  no_input_reg : IF g_pipeline_input=0 GENERATE

    reg_dat <= nxt_reg_dat;

    reg_acc <= nxt_reg_acc;

  END GENERATE;

  gen_input_reg : IF g_pipeline_input>0 GENERATE

    p_reg : PROCESS(clk)

    BEGIN

      IF rising_edge(clk) THEN

        IF clken='1' THEN

          reg_dat <= nxt_reg_dat;

          reg_acc <= nxt_reg_acc;

        END IF;

      END IF;

    END PROCESS;

  END GENERATE;

  ------------------------------------------------------------------------------

  -- Adder for the external accumulator

  ------------------------------------------------------------------------------

  u_adder : ENTITY common_add_sub_lib.common_add_sub

  GENERIC MAP (

    g_direction       => "ADD",

    g_representation  => "SIGNED",  -- not relevant because g_out_dat_w = g_in_dat_w

    g_pipeline_input  => 0,

    g_pipeline_output => g_pipeline_output,

    g_in_dat_w        => g_acc_w,

    g_out_dat_w       => g_acc_w

  )

  PORT MAP (

    clk     => clk,

    clken   => clken,

    in_a    => reg_dat,

    in_b    => reg_acc,

    result  => out_acc

  );

  ------------------------------------------------------------------------------

  -- Parallel output control pipeline

  ------------------------------------------------------------------------------

  in_val_slv(0) <= in_val;

  out_val       <= out_val_slv(0);

  u_out_val : ENTITY common_components_lib.common_pipeline

  GENERIC MAP (

    g_representation => "UNSIGNED",

    g_pipeline       => c_pipeline,

    g_reset_value    => 0,

    g_in_dat_w       => 1,

    g_out_dat_w      => 1

  )

  PORT MAP (

    clk     => clk,

    clken   => clken,

    in_dat  => slv(in_val),

    out_dat => out_val_slv

  );

END rtl;