Subversion Repositories astron_r2sdf_fft

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--

-- 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.

--

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

-- Purpose: Pipelined radix 2 FFT

-- Description: ASTRON-RP-755

-- Remarks: doc/readme.txt

library ieee, common_pkg_lib, astron_requantize_lib;

use IEEE.std_logic_1164.all;

use common_pkg_lib.common_pkg.all;

use work.twiddlesPkg.all;

use work.rTwoSDFPkg.all;

entity rTwoSDF is

  generic (

    -- generics for the FFT    

    g_nof_chan    : natural := 0;     -- Exponent of nr of subbands (0 means 1 subband)

    g_use_reorder : boolean := true;

    g_in_dat_w    : natural := 8;     -- number of input bits

    g_out_dat_w   : natural := 14;    -- number of output bits

    g_stage_dat_w : natural := 18;    -- number of bits used between the stages

    g_guard_w     : natural := 2;     -- guard bits are used to avoid overflow in single FFT stage.   

    g_nof_points  : natural := 1024;  -- N point FFT

    -- generics for rTwoSDFStage

    g_pipeline    : t_fft_pipeline := c_fft_pipeline

  );

  port (

    clk      : in  std_logic;

    rst      : in  std_logic := '0';

    in_re    : in  std_logic_vector(g_in_dat_w-1 downto 0);

    in_im    : in  std_logic_vector(g_in_dat_w-1 downto 0);

    in_val   : in  std_logic := '1';

    out_re   : out std_logic_vector(g_out_dat_w-1 downto 0);

    out_im   : out std_logic_vector(g_out_dat_w-1 downto 0);

    out_val  : out std_logic

  );

end entity rTwoSDF;

architecture str of rTwoSDF is

  constant c_nof_stages         : natural := ceil_log2(g_nof_points);

  constant c_stage_offset       : natural := 0;                               -- In "normal" pipelined fft operation the stage offset is 0

  constant c_twiddle_offset     : natural := 0;                               -- In "normal" pipelined fft operation the twiddle offset is 0

  -- Round last stage output to g_out_dat_w if g_out_dat_w < g_stage_dat_w else resize to g_out_dat_w

  constant c_out_scale_w        : integer := g_stage_dat_w - g_out_dat_w;     -- Estimate number of LSBs to round throw away when > 0 or insert when < 0

  -- Scale the input to make optimal use of the g_stage_dat_w of the stages, using a margin of g_guard_w to account for factor > 2 gain of the first stage

  constant c_in_scale_w         : natural := g_stage_dat_w - g_guard_w - g_in_dat_w; -- use type natural instead of integer to implicitly ensure that the g_stage_dat_w >= g_input_dat_w

  -- number the stage instances from c_nof_stages:1

  -- . the data input for the first stage has index c_nof_stages

  -- . the data output of the last stage has index 0

  type t_data_arr is array(c_nof_stages downto 0) of std_logic_vector(g_stage_dat_w-1 downto 0);

  signal data_re      : t_data_arr;

  signal data_im      : t_data_arr;

  signal data_val     : std_logic_vector(c_nof_stages downto 0):= (others=>'0');

  signal out_cplx     : std_logic_vector(2*g_stage_dat_w-1 downto 0);

  signal raw_out_cplx : std_logic_vector(2*g_stage_dat_w-1 downto 0);

  signal raw_out_re   : std_logic_vector(g_stage_dat_w-1 downto 0);

  signal raw_out_im   : std_logic_vector(g_stage_dat_w-1 downto 0);

  signal raw_out_val  : std_logic;

begin

  -- Inputs

  data_re( c_nof_stages) <= scale_and_resize_svec(in_re, c_in_scale_w, g_stage_dat_w);

  data_im( c_nof_stages) <= scale_and_resize_svec(in_im, c_in_scale_w, g_stage_dat_w);

  data_val(c_nof_stages) <= in_val;

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

  -- pipelined FFT stages

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

  gen_fft: for stage in c_nof_stages downto 1 generate

    u_stage : entity work.rTwoSDFStage

    generic map (

      g_nof_chan       => g_nof_chan,

      g_stage          => stage,

      g_stage_offset   => c_stage_offset,

      g_twiddle_offset => c_twiddle_offset,

      g_scale_enable   => sel_a_b(stage <= g_guard_w, FALSE, TRUE),  -- On average all stages have a gain factor of 2 therefore each stage needs to round 1 bit except for the last g_guard_w nof stages due to the input c_in_scale_w

      g_pipeline       => g_pipeline

    )

    port map (

      clk       => clk,

      rst       => rst,

      in_re     => data_re(stage),

      in_im     => data_im(stage),

      in_val    => data_val(stage),

      out_re    => data_re(stage-1),

      out_im    => data_im(stage-1),

      out_val   => data_val(stage-1)

    );

  end generate;

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

  -- Optional output reorder

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

  no_reorder : if g_use_reorder=false generate

    raw_out_re  <= data_re(0);

    raw_out_im  <= data_im(0);

    raw_out_val <= data_val(0);

  end generate;

  gen_reorder : if g_use_reorder=true generate

    raw_out_cplx <= data_im(0) & data_re(0);

    raw_out_re <= out_cplx(  g_stage_dat_w-1 downto 0);

    raw_out_im <= out_cplx(2*g_stage_dat_w-1 downto g_stage_dat_w);

    u_cplx: entity work.rTwoOrder

    generic map (

      g_nof_points => g_nof_points,

      g_nof_chan   => g_nof_chan

    )

    port map (

      clk     => clk,

      rst     => rst,

      in_dat  => raw_out_cplx,

      in_val  => data_val(0),

      out_dat => out_cplx,

      out_val => raw_out_val

    );

  end generate;

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

  -- pipelined FFT output requantization

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

  u_requantize_re : entity astron_requantize_lib.common_requantize

  generic map (

    g_representation      => "SIGNED",

    g_lsb_w               => c_out_scale_w,

    g_lsb_round           => TRUE,

    g_lsb_round_clip      => FALSE,

    g_msb_clip            => FALSE,

    g_msb_clip_symmetric  => FALSE,

    g_pipeline_remove_lsb => 0,

    g_pipeline_remove_msb => 0,

    g_in_dat_w            => g_stage_dat_w,

    g_out_dat_w           => g_out_dat_w

  )

  port map (

    clk        => clk,

    clken      => '1',

    in_dat     => raw_out_re,

    out_dat    => out_re,

    out_ovr    => open

  );

  u_requantize_im : entity astron_requantize_lib.common_requantize

  generic map (

    g_representation      => "SIGNED",

    g_lsb_w               => c_out_scale_w,

    g_lsb_round           => TRUE,

    g_lsb_round_clip      => FALSE,

    g_msb_clip            => FALSE,

    g_msb_clip_symmetric  => FALSE,

    g_pipeline_remove_lsb => 0,

    g_pipeline_remove_msb => 0,

    g_in_dat_w            => g_stage_dat_w,

    g_out_dat_w           => g_out_dat_w

  )

  port map (

    clk        => clk,

    clken      => '1',

    in_dat     => raw_out_im,

    out_dat    => out_im,

    out_ovr    => open

  );

  -- Valid Output

  out_val <= raw_out_val;

end str;