Clarify WPFB settings for L2TS.

applications/lofar2/libraries/sdp/src/vhdl/sdp_pkg.vhd

@@ -100,7 +100,7 @@ PACKAGE sdp_pkg is
   CONSTANT c_sdp_W_statistic_sz            : NATURAL := 2;   -- = c_sdp_W_statistic / c_word_w
   CONSTANT c_sdp_W_sub_weight              : NATURAL := 16;  -- = w in s(w, p), s = signed
   CONSTANT c_sdp_W_sub_weight_fraction     : NATURAL := 14;  -- = p in s(w, p)
-  CONSTANT c_sdp_W_sub_weight_magnitude    : NATURAL := c_sdp_W_sub_weight - c_sdp_W_sub_weight_fraction - 1;  -- = 2
+  CONSTANT c_sdp_W_sub_weight_magnitude    : NATURAL := c_sdp_W_sub_weight - c_sdp_W_sub_weight_fraction - 1;  -- = 1
   CONSTANT c_sdp_W_beamlet_scale           : NATURAL := 16;  -- = w in u(w, p), u = unsigned
   CONSTANT c_sdp_W_beamlet_scale_fraction  : NATURAL := 15;  -- = p in u(w, p)
   CONSTANT c_sdp_W_beamlet_scale_magnitude : NATURAL := c_sdp_W_beamlet_scale - c_sdp_W_beamlet_scale_fraction;  -- = 1
@@ -159,9 +159,11 @@ PACKAGE sdp_pkg is
   -- . g_fft_guard_w = 1 (was 2)
   --CONSTANT c_sdp_wpfb_subbands : t_wpfb :=
   --  (1, c_sdp_N_fft, 0, c_sdp_P_pfb,
-  --  c_sdp_N_taps, 0, c_sdp_W_adc, 17, c_sdp_W_fir_coef,
-  --  true, false, true, 17, c_sdp_W_subband, 0, 22, 1, true, 54, c_sdp_W_statistic_sz, 195313,
-  --  c_fft_pipeline, c_fft_pipeline, c_fil_ppf_pipeline);  -- = c_wpfb_lofar2_subbands_lts_2021
+  --   c_sdp_N_taps, 0, c_sdp_W_adc, 17, c_sdp_W_fir_coef,
+  --   true, false, true,
+  --   17, c_sdp_W_subband, 0, 22, 1, true,
+  --   54, c_sdp_W_statistic_sz, 195313,
+  --   c_fft_pipeline, c_fft_pipeline, c_fil_ppf_pipeline);  -- = c_wpfb_lofar2_subbands_lts_2021
 
   -- DTS 2022-04-04, changes based on results from  in tb_tb_verify_pfb_wg.vhd:
   -- . fil_backoff_w = 1
@@ -171,16 +173,43 @@ PACKAGE sdp_pkg is
   -- . g_fft_guard_w = 1
   --CONSTANT c_sdp_wpfb_subbands : t_wpfb :=
   --  (1, c_sdp_N_fft, 0, c_sdp_P_pfb,
-  --  c_sdp_N_taps, 1, c_sdp_W_adc, 23, c_sdp_W_fir_coef,
-  --  true, false, true, 23, c_sdp_W_subband, 1, 24, 1, true, 54, c_sdp_W_statistic_sz, 195313,
-  --  c_fft_pipeline, c_fft_pipeline, c_fil_ppf_pipeline);  -- = c_wpfb_lofar2_subbands_dts_18b
+  --   c_sdp_N_taps, 1, c_sdp_W_adc, 23, c_sdp_W_fir_coef,
+  --   true, false, true,
+  --   23, c_sdp_W_subband, 1, 24, 1, true,
+  --   54, c_sdp_W_statistic_sz, 195313,
+  --   c_fft_pipeline, c_fft_pipeline, c_fil_ppf_pipeline);  -- = c_wpfb_lofar2_subbands_dts_18b
 
   -- L2TS
+  -- . Use fft_guard_w = 1, instead of 2 to avoid overflow in first FFT stage,
+  --   because fil_backoff_w = 1 already provides sufficient FFT input margin
+  -- . Use fft_out_gain_w = 1 + 1 = 2. One to compensate for fil_backoff_w
+  --   = 1 and one to preserve the W_fft_proc = 5b while using fft_out_dat_w
+  --   = c_sdp_W_subband = 18b instead of 19b, to fit a 18x19 multiplier for
+  --   SST.
+  -- . From hdl/libraries/base/common/python/try_round_weight.py it follows
+  --   that using -r = 6 extra internal bits per stage is sufficient to have
+  --   < 1% disturbance on the sigma of the subband noise. The disturbance
+  --   on the sigma is about proportional to 1/2**r, so with -r = 4 it is
+  --   about < 4%. Therefore use fft_stage_dat_w = fft_out_dat_w +
+  --   fft_out_gain_w + 6b = 26b.
+  -- . The raw_dat_w for FFT output of real input is fft_stage_dat_w + 1,
+  --   because the use_separate in the FFT feature does not divide by 2.
+  --   This implies that preferrably fft_stage_dat_w <= 26, to fit the 18x27
+  --   multiplier resources.
+  CONSTANT c_sdp_W_fil_backoff             : NATURAL := 1;
+  CONSTANT c_sdp_W_fft_guard               : NATURAL := 1;
+  CONSTANT c_sdp_W_fft_stage_dat           : NATURAL := 24;  -- TODO try 26b, compare synthesis results
+  CONSTANT c_sdp_W_fft_in_dat              : NATURAL := c_sdp_W_fft_stage_dat - c_sdp_W_fft_guard;
+  CONSTANT c_sdp_W_fft_out_gain            : NATURAL := 2;
+  CONSTANT c_sdp_W_stat_data               : NATURAL := c_sdp_W_subband * 2 + ceil_log2(c_sdp_N_int_sub_hi);  -- = 54
+
   CONSTANT c_sdp_wpfb_subbands : t_wpfb :=
     (1, c_sdp_N_fft, 0, c_sdp_P_pfb,
-    c_sdp_N_taps, 1, c_sdp_W_adc, 23, c_sdp_W_fir_coef,
-    true, false, true, 23, c_sdp_W_subband, 2, 24, 1, true, 54, c_sdp_W_statistic_sz, 195313,
-    c_fft_pipeline, c_fft_pipeline, c_fil_ppf_pipeline);  -- = c_wpfb_lofar2_subbands_l2ts_18b
+     c_sdp_N_taps, c_sdp_W_fil_backoff, c_sdp_W_adc, c_sdp_W_fft_in_dat, c_sdp_W_fir_coef,
+     true, false, true,
+     c_sdp_W_fft_in_dat, c_sdp_W_subband, c_sdp_W_fft_out_gain, c_sdp_W_fft_stage_dat, c_sdp_W_fft_guard, true,
+     c_sdp_W_stat_data, c_sdp_W_statistic_sz, c_sdp_N_int_sub_hi,
+     c_fft_pipeline, c_fft_pipeline, c_fil_ppf_pipeline);  -- = c_wpfb_lofar2_subbands_l2ts_18b
 
   CONSTANT c_sdp_wpfb_complex_subbands : t_wpfb := func_wpfb_map_real_input_wpfb_parameters_to_complex_input(c_sdp_wpfb_subbands);