New LF edge detection algorithm + lowpass filter

This is a new LF edge detection algorithm for the FPGA.

- It uses a low-pass IIR filter to clean the signal
(see https://fail0verflow.com/blog/2014/proxmark3-fpga-iir-filter.html)
- The algorithm is able to detect consecutive peaks in the same
  direction
- It uses an envelope follower to dynamically adjust the peak thresholds
- The main threshold used in the envelope follower can be set from the ARM side

fpga/lf_edge_detect.v,
fpga/lp20khz_1MSa_iir_filter.v,
fpga/min_max_tracker.v: New file.

fpga/lo_edge_detect.v, fpga/fpga_lf.v: Modify accordingly.

armsrc/apps.h (FPGA_CMD_SET_USER_BYTE1,
FPGA_CMD_SET_EDGE_DETECT_THRESHOLD): New FPGA command.
fpga/fpga_lf.v: Modify accordingly/Add a 8bit user register.

fpga/fpga_lf.bit: Update accordingly.

fpga/tests: New directory for testbenches

fpga/tests/Makefile: New file. It compiles the testbenches
and runs all the tests by default (comparing with the golden output)

fpga/tests/tb_lp20khz_1MSa_iir_filter.v,
fpga/tests/tb_min_max_tracker.v,
fpga/tests/tb_lf_edge_detect.v: New testbenches

fpga/tests/plot_edgedetect.py: New script to plot the results from
the edge detection tests.

fpga/tests/tb_data: New directory for data and golden outputs

fpga/lo_edge_detect.v

@@ -1,21 +1,34 @@
 //-----------------------------------------------------------------------------
-// The way that we connect things in low-frequency simulation mode. In this
-// case just pass everything through to the ARM, which can bit-bang this
-// (because it is so slow).
+// Copyright (C) 2014 iZsh <izsh at fail0verflow.com>
 //
-// Jonathan Westhues, April 2006
-// iZsh <izsh at fail0verflow.com>, June 2014
+// 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.
 //-----------------------------------------------------------------------------
+//
+// There are two modes:
+// - lf_ed_toggle_mode == 0: the output is set low (resp. high) when a low
+//   (resp. high) edge/peak is detected, with hysteresis
+// - lf_ed_toggle_mode == 1: the output is toggling whenever an edge/peak
+//   is detected.
+//   That way you can detect two consecutive edges/peaks at the same level (L/H)
+//
+// Output:
+// - ssp_frame (wired to TIOA1 on the arm) for the edge detection/state
+// - ssp_clk: cross_lo
+`include "lp20khz_1MSa_iir_filter.v"
+`include "lf_edge_detect.v"
 
 module lo_edge_detect(
-	input pck0, input [7:0] pck_cnt, input pck_divclk,
-	output pwr_lo, output pwr_hi,
-	output pwr_oe1, output pwr_oe2, output pwr_oe3, output pwr_oe4,
-	input [7:0] adc_d, output adc_clk,
-	output ssp_frame, input ssp_dout, output ssp_clk,
-	input cross_lo,
-	output dbg,
-	input lf_field
+    input pck0, input pck_divclk,
+    output pwr_lo, output pwr_hi,
+    output pwr_oe1, output pwr_oe2, output pwr_oe3, output pwr_oe4,
+    input [7:0] adc_d, output adc_clk,
+    output ssp_frame, input ssp_dout, output ssp_clk,
+    input cross_lo,
+    output dbg,
+    input lf_field,
+    input lf_ed_toggle_mode, input [7:0] lf_ed_threshold
 );
 
 wire tag_modulation = ssp_dout & !lf_field;
@@ -29,34 +42,25 @@ assign pwr_oe4 = tag_modulation;
 assign ssp_clk = cross_lo;
 assign pwr_lo = reader_modulation;
 assign pwr_hi = 1'b0;
-assign dbg = ssp_frame;
 
-assign adc_clk = ~pck_divclk;
+// filter the ADC values
+wire data_rdy;
+wire [7:0] adc_filtered;
+assign adc_clk = pck0;
+lp20khz_1MSa_iir_filter adc_filter(pck0, adc_d, data_rdy, adc_filtered);
 
-// Toggle the output with hysteresis
-//  Set to high if the ADC value is above 200
-//  Set to low if the ADC value is below 64
-reg is_high;
-reg is_low;
-reg output_state;
+// detect edges
+wire [7:0] high_threshold, highz_threshold, lowz_threshold, low_threshold;
+wire [7:0] max, min;
+wire edge_state, edge_toggle;
+lf_edge_detect lf_ed(pck0, adc_filtered, lf_ed_threshold,
+	max, min,
+	high_threshold, highz_threshold, lowz_threshold, low_threshold,
+	edge_state, edge_toggle);
 
-always @(posedge pck0)
-begin
-	if((pck_cnt == 8'd7) && !pck_divclk) begin
-		is_high = (adc_d >= 8'd190);
-		is_low = (adc_d <= 8'd70);
-	end
-end
+assign dbg = lf_ed_toggle_mode ? edge_toggle : edge_state;
 
-always @(posedge is_high or posedge is_low)
-begin
-	if(is_high)
-		output_state <= 1'd1;
-	else if(is_low)
-		output_state <= 1'd0;
-end
-
-assign ssp_frame = output_state;
+assign ssp_frame = lf_ed_toggle_mode ? edge_toggle : edge_state;
 
 endmodule