fixing iso14443b (issue #103): fix timing issue (speeding up

[proxmark3-svn] / fpga / min_max_tracker.v

//-----------------------------------------------------------------------------
// 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 therefore can't 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