Subversion Repositories astron_wb_fft

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

--

-- 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;

use IEEE.std_logic_1164.all;

use common_pkg_lib.common_pkg.all;

package fft_pkg is

  -- FFT parameters for pipelined FFT (fft_pipe), parallel FFT (fft_par) and wideband FFT (fft_wide)

  type t_fft is record

    use_reorder    : boolean;  -- = false for bit-reversed output, true for normal output

    use_fft_shift  : boolean;  -- = false for [0, pos, neg] bin frequencies order, true for [neg, 0, pos] bin frequencies order in case of complex input

    use_separate   : boolean;  -- = false for complex input, true for two real inputs

    nof_chan       : natural;  -- = default 0, defines the number of channels (=time-multiplexed input signals): nof channels = 2**nof_chan 

    wb_factor      : natural;  -- = default 1, wideband factor

    twiddle_offset : natural;  -- = default 0, twiddle offset for PFT sections in a wideband FFT

    nof_points     : natural;  -- = 1024, N point FFT

    in_dat_w       : natural;  -- = 8,  number of input bits

    out_dat_w      : natural;  -- = 13, number of output bits

    out_gain_w     : natural;  -- = 0, output gain factor applied after the last stage output, before requantization to out_dat_w

    stage_dat_w    : natural;  -- = 18, data width used between the stages(= DSP multiplier-width)

    guard_w        : natural;  -- = 2, guard used to avoid overflow in first FFT stage, compensated in last guard_w nof FFT stages. 

                               --   on average the gain per stage is 2 so guard_w = 1, but the gain can be 1+sqrt(2) [Lyons section

                               --   12.3.2], therefore use input guard_w = 2.

    guard_enable   : boolean;  -- = true when input needs guarding, false when input requires no guarding but scaling must be

                               --   skipped at the last stage(s) compensate for input guard (used in wb fft with pipe fft section

                               --   doing the input guard and par fft section doing the output compensation)

    stat_data_w    : positive; -- = 56

    stat_data_sz   : positive; -- = 2

  end record;

  constant c_fft   : t_fft := (true, false, true, 0, 4, 0, 1024, 8, 14, 0, c_dsp_mult_w, 2, true, 56, 2);

  -- Check consistancy of the FFT parameters

  function fft_r2_parameter_asserts(g_fft : t_fft) return boolean;  -- the return value is void, because always true or abort due to failure

  -- Definitions for fft slv array (an array can not have unconstraint elements, so choose sufficiently wide 32 bit slv elements)

  subtype  t_fft_slv_arr is t_slv_32_arr;    -- use subtype to ease interfacing to existing types and to have central definition for rtwo components

  constant c_fft_slv_w  : natural := 32;    -- match slv width of t_fft_slv_arr

  function to_fft_svec(n : integer) return std_logic_vector;                 -- map to c_fft_slv_w wide slv, no need for to_rtwo_uvec, because natural is subtype of integer

  function resize_fft_uvec(vec : std_logic_vector) return std_logic_vector;  -- map to c_fft_slv_w wide slv

  function resize_fft_svec(vec : std_logic_vector) return std_logic_vector;  -- map to c_fft_slv_w wide slv

  -- FFT shift swaps right and left half of bin axis to shift zero-frequency component to center of spectrum

  function fft_shift(bin : std_logic_vector) return std_logic_vector;

  function fft_shift(bin, w : natural) return natural;

end package fft_pkg;

package body fft_pkg is

  function fft_r2_parameter_asserts(g_fft : t_fft) return boolean is

  begin

    -- nof_points

    assert g_fft.nof_points=2**true_log2(g_fft.nof_points) report "fft_r2: nof_points must be a power of 2" severity failure;

    -- wb_factor

    assert g_fft.wb_factor=2**true_log2(g_fft.wb_factor) report "fft_r2: wb_factor must be a power of 2" severity failure;

    -- use_reorder

    if g_fft.use_reorder=false then

      assert g_fft.use_separate=false  report "fft_r2 : without use_reorder there cannot be use_separate for two real inputs" severity failure;

      assert g_fft.use_fft_shift=false report "fft_r2 : without use_reorder there cannot be use_fft_shift for complex input"  severity failure;

    end if;

    -- use_separate

    if g_fft.use_separate=true then

      assert g_fft.use_fft_shift=false report "fft_r2 : with use_separate there cannot be use_fft_shift for two real inputs"  severity failure;

    end if;

    return true;

  end;

  function to_fft_svec(n : integer) return std_logic_vector is

  begin

    return RESIZE_SVEC(TO_SVEC(n, 32), c_fft_slv_w);

  end;

  function resize_fft_uvec(vec : std_logic_vector) return std_logic_vector is

  begin

    return RESIZE_UVEC(vec, c_fft_slv_w);

  end;

  function resize_fft_svec(vec : std_logic_vector) return std_logic_vector is

  begin

    return RESIZE_SVEC(vec, c_fft_slv_w);

  end;

  function fft_shift(bin : std_logic_vector) return std_logic_vector is

    constant c_w   : natural := bin'length;

    variable v_bin : std_logic_vector(c_w-1 downto 0) := bin;

  begin

    return not v_bin(c_w-1) & v_bin(c_w-2 downto 0);  -- invert MSbit for fft_shift

  end;

  function fft_shift(bin, w : natural) return natural is

  begin

    return TO_UINT(fft_shift(TO_UVEC(bin, w)));

  end;

end fft_pkg;