Hitag fixes (#887)
[proxmark3-svn] / 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: // initialize
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: // high phase
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: // low phase
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
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