lf_edge_detect.v

//-----------------------------------------------------------------------------
// Copyright (C) Proxmark3 contributors. See AUTHORS.md for details.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// See LICENSE.txt for the text of the license.
//-----------------------------------------------------------------------------

module lf_edge_detect(
    input clk,
    input [7:0] adc_d,
    input [7:0] lf_ed_threshold,

    output [7:0] max,
    output [7:0] min,
    output [7:0] low_threshold,
    output [7:0] high_threshold,
    output [7:0] lowz_threshold,
    output [7:0] highz_threshold,
    output edge_state,
    output edge_toggle
);

min_max_tracker tracker(
    .clk       (clk),
    .adc_d     (adc_d),
    .threshold (lf_ed_threshold),
    .min       (min),
    .max       (max)
);

// auto-tune
assign high_threshold  = (max + min) / 2 + (max - min) / 4;
assign highz_threshold = (max + min) / 2 + (max - min) / 8;
assign lowz_threshold  = (max + min) / 2 - (max - min) / 8;
assign low_threshold   = (max + min) / 2 - (max - min) / 4;

// heuristic to see if it makes sense to try to detect an edge
wire enabled =
    (high_threshold > highz_threshold)
    & (highz_threshold > lowz_threshold)
    & (lowz_threshold > low_threshold)
    & ((high_threshold - highz_threshold) > 8)
    & ((highz_threshold - lowz_threshold) > 16)
    & ((lowz_threshold - low_threshold) > 8);

// Toggle the output with hysteresis
// Set to high if the ADC value is above the threshold
// Set to low if the ADC value is below the threshold
reg is_high = 0;
reg is_low = 0;
reg is_zero = 0;
reg trigger_enabled = 1;
reg output_edge = 0;
reg output_state;

always @(posedge clk)
begin
    is_high <= (adc_d >= high_threshold);
    is_low  <= (adc_d <= low_threshold);
    is_zero <= ((adc_d > lowz_threshold) & (adc_d < highz_threshold));
end

// all edges detection
always @(posedge clk)
if (enabled)
begin
    // To enable detecting two consecutive peaks at the same level
    // (low or high) we check whether or not we went back near 0 in-between.
    // This extra check is necessary to prevent from noise artifacts
    // around the threshold values.
    if (trigger_enabled & (is_high | is_low))
    begin
        output_edge <= ~output_edge;
        trigger_enabled <= 0;
    end
    else
        trigger_enabled <= trigger_enabled | is_zero;
end

// edge states
always @(posedge clk)
if (enabled)
begin
    if (is_high)
        output_state <= 1'd1;
    else if (is_low)
        output_state <= 1'd0;
end

assign edge_state  = output_state;
assign edge_toggle = output_edge;

endmodule