Subversion Repositories astron_wb_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:  Complex Pipelined Fast Fourier Transform

-- 

-- Description: The fft_r2_pipe unit performs a complex pipelined FFT on the incoming data stream.

--              The implementation is pipelined which means that at every stage only one 

--              multiplier is used to perform all N/2 twiddle multiplications. 

--              

--              There are two optional features: 

--              

--              * Reordering: When enabled the output bins of the FFT are re-ordered in 

--                            in such a way that the bins represent the frequencies in an 

--                            incrementing way. 

--              

--              * Separation: When enabled the fft_r2_pipe can be used to process two real streams.

--                            The first real stream (A) presented on the real input, the second 

--                            real stream (B) presented on the imaginary input. 

--                            The separation unit processes outputs the spectrum of A and B in 

--                            an alternating way: A(0), B(0), A(1), B(1).... etc

--

--

-- Remarks: When g_fft.nof_chan is used the spectrums at the output will be interleaved

--          per spectrum and NOT per sample. So in case g_fft.nof_chan = 1 there will be

--          two multiplexed channels at the input (c0t0 means channel 0, timestamp 0) :

--         

--          c0t0 c1t0s c0t1 c1t1 c0t2 c1t2 ... c0t15 c1t15 

--

--          At the output will find: 

--

--          c0f0 c0f1 c0f2 ... c0f15 c1f0 c1f1 c1f2 ... c1f15  (c0f0 means channel 0, frequency bin 0)

--

--           

library ieee, common_pkg_lib, common_components_lib,  common_requantize_lib, rTwoSDF_lib;

use IEEE.std_logic_1164.all;

use common_pkg_lib.common_pkg.all;

use rTwoSDF_lib.rTwoSDFPkg.all;

use work.fft_pkg.all;

entity fft_r2_pipe is

  generic (

    g_fft      : t_fft := c_fft;                   -- generics for the FFT

    g_pipeline : t_fft_pipeline := c_fft_pipeline; -- generics for pipelining in each stage, defined in rTwoSDF_lib.rTwoSDFPkg

    g_dont_flip_channels : boolean := false        -- generic to prevent re-ordering of the channels

  );

  port (

    clk      : in  std_logic;

    rst      : in  std_logic := '0';

    in_re    : in  std_logic_vector(g_fft.in_dat_w-1 downto 0);

    in_im    : in  std_logic_vector(g_fft.in_dat_w-1 downto 0);

    in_val   : in  std_logic := '1';

    out_re   : out std_logic_vector(g_fft.out_dat_w-1 downto 0);

    out_im   : out std_logic_vector(g_fft.out_dat_w-1 downto 0);

    out_val  : out std_logic

  );

end entity fft_r2_pipe;

architecture str of fft_r2_pipe is

  constant c_pipeline_remove_lsb : natural := 0;

  constant c_nof_stages         : natural := ceil_log2(g_fft.nof_points);

  constant c_stage_offset       : natural := true_log2(g_fft.wb_factor);                         -- Stage offset is required for twiddle generation in wideband fft

  constant c_in_scale_w         : natural := g_fft.stage_dat_w - g_fft.in_dat_w - sel_a_b(g_fft.guard_enable, g_fft.guard_w, 0);

  constant c_out_scale_w        : integer := g_fft.stage_dat_w - g_fft.out_dat_w - g_fft.out_gain_w;  -- Estimate number of LSBs to throw throw away when > 0 or insert when < 0

  -- 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_fft.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(c_nof_complex*g_fft.stage_dat_w-1 downto 0);

  signal in_cplx      : std_logic_vector(c_nof_complex*g_fft.stage_dat_w-1 downto 0);

  signal raw_out_re   : std_logic_vector(g_fft.stage_dat_w-1 downto 0);

  signal raw_out_im   : std_logic_vector(g_fft.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_fft.stage_dat_w);

  data_im( c_nof_stages) <= scale_and_resize_svec(in_im, c_in_scale_w, g_fft.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 rTwoSDF_lib.rTwoSDFStage

    generic map (

      g_nof_chan       => g_fft.nof_chan,

      g_stage          => stage,

      g_stage_offset   => c_stage_offset,

      g_twiddle_offset => g_fft.twiddle_offset,

      g_scale_enable   => sel_a_b(stage <= g_fft.guard_w, FALSE, TRUE),

      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 and separation

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

  gen_reorder_and_separate : if(g_fft.use_separate or g_fft.use_reorder) generate

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

    u_reorder_sep : entity work.fft_reorder_sepa_pipe

    generic map (

      g_bit_flip    => g_fft.use_reorder,

      g_fft_shift   => g_fft.use_fft_shift,

      g_separate    => g_fft.use_separate,

      g_dont_flip_channels => g_dont_flip_channels,

      g_nof_points  => g_fft.nof_points,

      g_nof_chan    => g_fft.nof_chan

    )

    port map (

      clk     => clk,

      rst     => rst,

      in_dat  => in_cplx,

      in_val  => data_val(0),

      out_dat => out_cplx,

      out_val => raw_out_val

    );

    raw_out_re <= out_cplx(  g_fft.stage_dat_w-1 downto 0);

    raw_out_im <= out_cplx(2*g_fft.stage_dat_w-1 downto g_fft.stage_dat_w);

  end generate;

  no_reorder_no_generate : if(g_fft.use_separate=false and g_fft.use_reorder=false) generate

    raw_out_re  <= data_re(0);

    raw_out_im  <= data_im(0);

    raw_out_val <= data_val(0);

  end generate;

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

  -- pipelined FFT output requantization

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

  u_requantize_re : entity common_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 => c_pipeline_remove_lsb,

    g_pipeline_remove_msb => 0,

    g_in_dat_w            => g_fft.stage_dat_w,

    g_out_dat_w           => g_fft.out_dat_w

  )

  port map (

    clk        => clk,

    in_dat     => raw_out_re,

    out_dat    => out_re,

    out_ovr    => open

  );

  u_requantize_im : entity common_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 => c_pipeline_remove_lsb,

    g_pipeline_remove_msb => 0,

    g_in_dat_w            => g_fft.stage_dat_w,

    g_out_dat_w           => g_fft.out_dat_w

  )

  port map (

    clk        => clk,

    in_dat     => raw_out_im,

    out_dat    => out_im,

    out_ovr    => open

  );

  -- Valid Output

  u_out_val : entity common_components_lib.common_pipeline_sl

  generic map (

    g_pipeline => c_pipeline_remove_lsb

  )

  port map (

    rst     => rst,

    clk     => clk,

    in_dat  => raw_out_val,

    out_dat => out_val

  );

end str;