New LF edge detection algorithm + lowpass filter

[proxmark3-svn] / fpga / min_max_tracker.v

diff --git a/fpga/min_max_tracker.v b/fpga/min_max_tracker.v
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+//-----------------------------------------------------------------------------
+// Copyright (C) 2014 iZsh <izsh at fail0verflow.com>
+//
+// This code is licensed to you under the terms of the GNU GPL, version 2 or,
+// at your option, any later version. See the LICENSE.txt file for the text of
+// the license.
+//-----------------------------------------------------------------------------
+// track min and max peak values (envelope follower)
+//
+// NB: the min value (resp. max value) is updated only when the next high peak
+// (resp. low peak) is reached/detected, since you can't know it isn't a
+// local minima (resp. maxima) until then.
+// This also means the peaks are detected with an unpredictable delay.
+// This algorithm can't therefore be used directly for realtime peak detections,
+// but it can be used as a simple envelope follower.
+module min_max_tracker(input clk, input [7:0] adc_d, input [7:0] threshold,
+       output [7:0] min, output [7:0] max);
+
+       reg [7:0] min_val = 255;
+       reg [7:0] max_val = 0;
+       reg [7:0] cur_min_val = 255;
+       reg [7:0] cur_max_val = 0;
+       reg [1:0] state = 0;
+
+       always @(posedge clk)
+       begin
+               case (state)
+               0:
+                       begin
+                               if (cur_max_val >= ({1'b0, adc_d} + threshold))
+                                       state <= 2;
+                               else if (adc_d >= ({1'b0, cur_min_val} + threshold))
+                                       state <= 1;
+                               if (cur_max_val <= adc_d)
+                                       cur_max_val <= adc_d;
+                               else if (adc_d <= cur_min_val)
+                                       cur_min_val <= adc_d;                                   
+                       end
+               1:
+                       begin
+                               if (cur_max_val <= adc_d)
+                                       cur_max_val <= adc_d;
+                               else if (({1'b0, adc_d} + threshold) <= cur_max_val) begin
+                                       state <= 2;
+                                       cur_min_val <= adc_d;
+                                       max_val <= cur_max_val;
+                               end
+                       end
+               2:
+                       begin
+                               if (adc_d <= cur_min_val)
+                                       cur_min_val <= adc_d;                                   
+                               else if (adc_d >= ({1'b0, cur_min_val} + threshold)) begin
+                                       state <= 1;
+                                       cur_max_val <= adc_d;
+                                       min_val <= cur_min_val;
+                               end
+                       end
+               endcase
+       end
+
+       assign min = min_val;
+       assign max = max_val;
+
+endmodule