fpga/min_max_tracker.v

   1 //-----------------------------------------------------------------------------
   2 // Copyright (C) 2014 iZsh <izsh at fail0verflow.com>
   3 //
   4 // This code is licensed to you under the terms of the GNU GPL, version 2 or,
   5 // at your option, any later version. See the LICENSE.txt file for the text of
   6 // the license.
   7 //-----------------------------------------------------------------------------
   8 // track min and max peak values (envelope follower)
   9 //
  10 // NB: the min value (resp. max value) is updated only when the next high peak
  11 // (resp. low peak) is reached/detected, since you can't know it isn't a
  12 // local minima (resp. maxima) until then.
  13 // This also means the peaks are detected with an unpredictable delay.
  14 // This algorithm therefore can't be used directly for realtime peak detections,
  15 // but it can be used as a simple envelope follower.
  16 module min_max_tracker(input clk, input [7:0] adc_d, input [7:0] threshold,
  17         output [7:0] min, output [7:0] max);
  18
  19         reg [7:0] min_val = 255;
  20         reg [7:0] max_val = 0;
  21         reg [7:0] cur_min_val = 255;
  22         reg [7:0] cur_max_val = 0;
  23         reg [1:0] state = 0;
  24
  25         always @(posedge clk)
  26         begin
  27                 case (state)
  28                 0:
  29                         begin
  30                                 if (cur_max_val >= ({1'b0, adc_d} + threshold))
  31                                         state <= 2;
  32                                 else if (adc_d >= ({1'b0, cur_min_val} + threshold))
  33                                         state <= 1;
  34                                 if (cur_max_val <= adc_d)
  35                                         cur_max_val <= adc_d;
  36                                 else if (adc_d <= cur_min_val)
  37                                         cur_min_val <= adc_d;
  38                         end
  39                 1:
  40                         begin
  41                                 if (cur_max_val <= adc_d)
  42                                         cur_max_val <= adc_d;
  43                                 else if (({1'b0, adc_d} + threshold) <= cur_max_val) begin
  44                                         state <= 2;
  45                                         cur_min_val <= adc_d;
  46                                         max_val <= cur_max_val;
  47                                 end
  48                         end
  49                 2:
  50                         begin
  51                                 if (adc_d <= cur_min_val)
  52                                         cur_min_val <= adc_d;
  53                                 else if (adc_d >= ({1'b0, cur_min_val} + threshold)) begin
  54                                         state <= 1;
  55                                         cur_max_val <= adc_d;
  56                                         min_val <= cur_min_val;
  57                                 end
  58                         end
  59                 endcase
  60         end
  61
  62         assign min = min_val;
  63         assign max = max_val;
  64
  65 endmodule