Use functions to defined FFT input and output widths.

libraries/dsp/fft/src/vhdl/fft_pkg.vhd

@@ -69,7 +69,12 @@ package fft_pkg is
   
   -- 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
-  
+
+  -- FFT input and output widths
+  function func_fft_in_scale_w(g_fft : t_fft) return natural;
+  function func_fft_raw_dat_w(g_fft : t_fft) return natural;
+  function func_fft_raw_fraction_w(g_fft : t_fft) return natural;
+
   -- 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
@@ -106,7 +111,31 @@ package body fft_pkg is
       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;    
+  end;
+
+  -- Scale input data to MSbits of stage data, with g_fft.guard_w bits backoff if g_fft.guard_enable = true
+  function func_fft_in_scale_w(g_fft : t_fft) return natural is
+    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);
+  begin
+    return c_in_scale_w;
+  end func_fft_in_scale_w;
+
+  -- Raw output data width is equal to the internal data width of the FFT
+  function func_fft_raw_dat_w(g_fft : t_fft) return natural is
+    constant c_sepa_growth_w  : natural := sel_a_b(g_fft.use_separate, 1, 0);  -- add one bit for add sub growth in separate
+    constant c_raw_dat_w      : natural := g_fft.stage_dat_w + c_sepa_growth_w;
+  begin
+    return c_raw_dat_w;
+  end func_fft_raw_dat_w;
+
+  -- Number of LSbits in the raw output data that represent the fraction bits in c_raw_dat_w.
+  function func_fft_raw_fraction_w(g_fft : t_fft) return natural is
+    constant c_raw_dat_w      : natural := func_fft_raw_dat_w(g_fft);
+    constant c_raw_fraction_w : natural := c_raw_dat_w - g_fft.out_dat_w - g_fft.out_gain_w;
+  begin
+    return c_raw_fraction_w;
+  end func_fft_raw_fraction_w;
+
 
   function to_fft_svec(n : integer) return std_logic_vector is
   begin

libraries/dsp/fft/src/vhdl/fft_r2_par.vhd

@@ -127,15 +127,12 @@ architecture str of fft_r2_par is
   constant c_pipeline_remove_lsb : natural := 1;
 
   constant c_nof_stages         : natural := ceil_log2(g_fft.nof_points);  
-  constant c_nof_bf_per_stage   : natural := g_fft.nof_points/2;  
-  constant c_in_scale_w_tester  : integer := g_fft.stage_dat_w - g_fft.in_dat_w - sel_a_b(g_fft.guard_enable, g_fft.guard_w, 0);
-  constant c_in_scale_w         : natural := sel_a_b(c_in_scale_w_tester > 0, c_in_scale_w_tester, 0);  -- Only scale when in_dat_w is not too big. 
-  
-  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 away when > 0 or insert when < 0
+  constant c_nof_bf_per_stage   : natural := g_fft.nof_points/2;
+
+  constant c_in_scale_w         : natural := func_fft_in_scale_w(g_fft);
+  constant c_raw_fraction_w     : natural := func_fft_raw_fraction_w(g_fft);
+  constant c_raw_dat_w          : natural := func_fft_raw_dat_w(g_fft);
 
-  constant c_sepa_growth_w      : natural := sel_a_b(g_fft.use_separate, 1, 0);  -- add one bit for add sub growth in separate
-  constant c_raw_dat_w          : natural := g_fft.stage_dat_w + c_sepa_growth_w;
-  
   type   t_stage_dat_arr   is array (integer range <>)     of std_logic_vector(g_fft.stage_dat_w-1 downto 0);
   type   t_stage_raw_arr   is array (integer range <>)     of std_logic_vector(c_raw_dat_w-1 downto 0);
   type   t_data_arr2       is array(c_nof_stages downto 0) of t_stage_dat_arr(g_fft.nof_points-1 downto 0);
@@ -158,6 +155,12 @@ architecture str of fft_r2_par is
   signal fft_im_arr       : t_stage_raw_arr(g_fft.nof_points-1 downto 0);
   signal fft_val          : std_logic;
 
+  -- debug signals to view parameters in Wave Window
+  signal dbg_g_g_fft          : t_fft := g_fft;
+  signal dbg_c_in_scale_w     : natural := c_in_scale_w;
+  signal dbg_c_raw_fraction_w : natural := c_raw_fraction_w;
+  signal dbg_c_raw_dat_w      : natural := c_raw_dat_w;
+
 begin
  
   ------------------------------------------------------------------------------
@@ -378,7 +381,7 @@ begin
     u_requantize_re : entity common_lib.common_requantize
     generic map (
       g_representation      => "SIGNED",      
-      g_lsb_w               => c_out_scale_w + c_sepa_growth_w,
+      g_lsb_w               => c_raw_fraction_w,
       g_lsb_round           => TRUE,           
       g_lsb_round_clip      => FALSE,      
       g_msb_clip            => FALSE,            
@@ -398,7 +401,7 @@ begin
     u_requantize_im : entity common_lib.common_requantize
     generic map (
       g_representation      => "SIGNED",      
-      g_lsb_w               => c_out_scale_w + c_sepa_growth_w,
+      g_lsb_w               => c_raw_fraction_w,
       g_lsb_round           => TRUE,           
       g_lsb_round_clip      => FALSE,      
       g_msb_clip            => FALSE,            

libraries/dsp/fft/src/vhdl/fft_r2_pipe.vhd

@@ -56,7 +56,19 @@
 --
 --   c0f0 c0f1 c0f2 ... c0f15 c1f0 c1f1 c1f2 ... c1f15  (c0f0 means channel 0, frequency bin 0)
 --
---           
+-- . Output subband widths:
+--   - out_quant_re/im : g_fft.out_dat_w bits (within c_32 word)
+--   - out_raw_re/im   : c_raw_dat_w bits (within c_32 word)
+--   The out_quant carries subbands of g_fft.out_dat_w bits, so the
+--   c_raw_fraction_w fraction bits in c_raw_dat_w have been rounded.
+--   The out_raw carries subbands of c_raw_dat_w bits, that still have the
+--   c_raw_fraction_w fraction bits. The out_raw subbands are suitable for
+--   further weighting or alternative rounding.
+--   Note that c_raw_dat_w and c_raw_fraction_w depend on g_fft.use_separate.
+--   For real input data FFT there is one fraction bit more than for complex
+--   input FFT, due to the adder stage in the separate function.
+--   Both out_quant and out_raw use FFT out_val, so they have the same timing.
+--
 
 library ieee, common_lib, rTwoSDF_lib;
 use IEEE.std_logic_1164.all;
@@ -88,7 +100,7 @@ end entity fft_r2_pipe;
 
 architecture str of fft_r2_pipe is
 
-  constant c_pipeline_remove_lsb : natural := 0;
+  constant c_pipeline_remove_lsb : natural := 1;  -- to easy timing closure
   
   constant c_switch_en          : boolean := g_fft.use_separate;  -- default do apply switch/unswitch per real input to mitigate quantization crosstalk
   constant c_switch_sz_w        : natural := ceil_log2(g_fft.nof_points) + g_fft.nof_chan;
@@ -96,11 +108,12 @@ architecture str of fft_r2_pipe is
   constant c_switch_seed1       : STD_LOGIC_VECTOR(c_fft_lfsr_len-1 DOWNTO 0) := fft_switch_new_seed(c_fft_switch_seed1, g_instance_index);
   constant c_switch_seed2       : STD_LOGIC_VECTOR(c_fft_lfsr_len-1 DOWNTO 0) := fft_switch_new_seed(c_fft_switch_seed2, g_instance_index);
   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
-  constant c_sepa_growth_w      : natural := sel_a_b(g_fft.use_separate, 1, 0);  -- add one bit for add sub growth in separate
-  constant c_raw_dat_w          : natural := g_fft.stage_dat_w + c_sepa_growth_w;
+  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 := func_fft_in_scale_w(g_fft);
+  constant c_raw_fraction_w     : natural := func_fft_raw_fraction_w(g_fft);
+  constant c_raw_dat_w          : natural := func_fft_raw_dat_w(g_fft);
+
   constant c_unswitch_dat_w     : natural := c_raw_dat_w;  -- no need for extra bit, because most negative value cannot occur in FFT output
 
   -- number the stage instances from c_nof_stages:1
@@ -134,8 +147,7 @@ architecture str of fft_r2_pipe is
   -- debug signals to view parameters in Wave Window
   signal dbg_g_g_fft          : t_fft := g_fft;
   signal dbg_c_in_scale_w     : natural := c_in_scale_w;
-  signal dbg_c_out_scale_w    : integer := c_out_scale_w;
-  signal dbg_c_sepa_growth_w  : natural := c_sepa_growth_w;
+  signal dbg_c_raw_fraction_w : natural := c_raw_fraction_w;
   signal dbg_c_raw_dat_w      : natural := c_raw_dat_w;
 
 begin
@@ -286,7 +298,7 @@ begin
   u_requantize_re : entity common_lib.common_requantize
   generic map (
     g_representation      => "SIGNED",      
-    g_lsb_w               => c_out_scale_w + c_sepa_growth_w,
+    g_lsb_w               => c_raw_fraction_w,
     g_lsb_round           => TRUE,           
     g_lsb_round_clip      => FALSE,      
     g_msb_clip            => FALSE,            
@@ -306,7 +318,7 @@ begin
   u_requantize_im : entity common_lib.common_requantize
   generic map (
     g_representation      => "SIGNED",      
-    g_lsb_w               => c_out_scale_w + c_sepa_growth_w,
+    g_lsb_w               => c_raw_fraction_w,
     g_lsb_round           => TRUE,           
     g_lsb_round_clip      => FALSE,      
     g_msb_clip            => FALSE,            
@@ -336,9 +348,10 @@ begin
 
   ------------------------------------------------------------------------------
   -- Pipelined FFT raw output register
-  -- . Pipeline out_raw_* to align with out_quant_*, so they can share out_val
   ------------------------------------------------------------------------------
 
+  -- . Pipeline out_raw to align with out_quant, so they can share
+  --   out_val.
   u_out_raw_re : entity common_lib.common_pipeline
   generic map (
     g_representation => "SIGNED",

libraries/dsp/fft/src/vhdl/fft_r2_wide.vhd

@@ -148,12 +148,9 @@ architecture rtl of fft_r2_wide is
   constant c_fft_r2_pipe_arr  : t_fft_arr(g_fft.wb_factor-1 downto 0) := func_create_generic_for_pipe_fft(g_fft); 
   constant c_fft_r2_par       : t_fft                                 := func_create_generic_for_par_fft(g_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 := c_fft_r2_par.out_dat_w - g_fft.out_dat_w - g_fft.out_gain_w;  -- Estimate number of LSBs to throw away when > 0 or insert when < 0
-
-  constant c_sepa_growth_w    : natural := sel_a_b(g_fft.use_separate, 1, 0);  -- add one bit for add sub growth in separate
-  constant c_raw_dat_w        : natural := g_fft.stage_dat_w + c_sepa_growth_w;
+  constant c_in_scale_w       : natural := func_fft_in_scale_w(g_fft);
+  constant c_raw_fraction_w   : natural := func_fft_raw_fraction_w(g_fft);
+  constant c_raw_dat_w        : natural := func_fft_raw_dat_w(g_fft);
 
   -- g_fft.wb_factor = 1
   signal fft_pipe_out_re      : std_logic_vector(g_fft.out_dat_w-1 downto 0);
@@ -182,8 +179,7 @@ architecture rtl of fft_r2_wide is
   -- debug signals to view parameters in Wave Window
   signal dbg_g_g_fft          : t_fft := g_fft;
   signal dbg_c_in_scale_w     : natural := c_in_scale_w;
-  signal dbg_c_out_scale_w    : integer := c_out_scale_w;
-  signal dbg_c_sepa_growth_w  : natural := c_sepa_growth_w;
+  signal dbg_c_raw_fraction_w : natural := c_raw_fraction_w;
   signal dbg_c_raw_dat_w      : natural := c_raw_dat_w;
 
 begin
@@ -328,7 +324,7 @@ begin
       u_requantize_output_re : entity common_lib.common_requantize
       generic map (
         g_representation      => "SIGNED",      
-        g_lsb_w               => c_out_scale_w + c_sepa_growth_w,
+        g_lsb_w               => c_raw_fraction_w,
         g_lsb_round           => TRUE,           
         g_lsb_round_clip      => FALSE,      
         g_msb_clip            => FALSE,            
@@ -348,7 +344,7 @@ begin
       u_requantize_output_im : entity common_lib.common_requantize
       generic map (
         g_representation      => "SIGNED",      
-        g_lsb_w               => c_out_scale_w + c_sepa_growth_w,
+        g_lsb_w               => c_raw_fraction_w,
         g_lsb_round           => TRUE,           
         g_lsb_round_clip      => FALSE,      
         g_msb_clip            => FALSE,