lf_edge_detect.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.
//-----------------------------------------------------------------------------
// input clk is 24Mhz
`include "min_max_tracker.v"

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

	min_max_tracker tracker(clk, adc_d, lf_ed_threshold, min, 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