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/tests/Makefile

@@ -0,0 +1,87 @@
+#-----------------------------------------------------------------------------
+# 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.
+#-----------------------------------------------------------------------------
+
+TEST_OUTDIR = tb_tmp
+
+TB_SOURCES = \
+	tb_lp20khz_1MSa_iir_filter.v \
+	tb_min_max_tracker.v \
+	tb_lf_edge_detect.v
+
+TBS = $(TB_SOURCES:.v=.vvp)
+
+TB_DATA = \
+	pcf7931_write1byte_1MSA_data \
+	pcf7931_read_1MSA_data
+
+all: $(TBS) tests
+
+%.vvp: %.v
+	iverilog -I .. -o $@ $<
+
+clean:
+	rm -rf *.vvp $(TEST_OUTDIR)
+
+tests: tb_lp20khz_1MSa_iir_filter tb_min_max_tracker tb_lf_edge_detect
+
+tb_lp20khz_1MSa_iir_filter: tb_lp20khz_1MSa_iir_filter.vvp | test_dir
+	@printf "Testing $@\n"
+	@for d in $(TB_DATA); do \
+		$(call run_test,$@.vvp,$$d,in); \
+		$(call check_golden,$$d,filtered); \
+	done; \
+	rm -f $(TEST_OUTDIR)/data.*
+
+tb_min_max_tracker: tb_min_max_tracker.vvp | test_dir
+	@printf "Testing $@\n"
+	@for d in $(TB_DATA); do \
+		$(call run_test,$@.vvp,$$d,in filtered.gold); \
+		$(call check_golden,$$d,min); \
+		$(call check_golden,$$d,max); \
+	done; \
+	rm -f $(TEST_OUTDIR)/data.*
+
+tb_lf_edge_detect: tb_lf_edge_detect.vvp | test_dir
+	@printf "Testing $@\n"
+	@for d in $(TB_DATA); do \
+		$(call run_test,$@.vvp,$$d,in filtered.gold); \
+		$(call check_golden,$$d,min); \
+		$(call check_golden,$$d,max); \
+		$(call check_golden,$$d,state); \
+		$(call check_golden,$$d,toggle); \
+		$(call check_golden,$$d,high); \
+		$(call check_golden,$$d,highz); \
+		$(call check_golden,$$d,lowz); \
+		$(call check_golden,$$d,low); \
+	done; \
+	rm -f $(TEST_OUTDIR)/data.*
+
+test_dir:
+	@if [ ! -d $(TEST_OUTDIR) ] ; then mkdir $(TEST_OUTDIR) ; fi
+
+.PHONY: all clean 
+
+# $(1) = basename
+# $(2) = extension to check
+check_golden = \
+	printf "        Checking $(1).$(2)... "; \
+	mv $(TEST_OUTDIR)/data.$(2) $(TEST_OUTDIR)/$(1).$(2); \
+	if cmp -s tb_data/$(1).$(2).gold $(TEST_OUTDIR)/$(1).$(2); then \
+		printf "OK\n"; \
+	else \
+		printf "ERROR\n"; \
+	fi
+
+# $(1) = vvp file
+# $(2) = data basename
+# $(3) = data extensions to copy
+run_test = \
+	env echo "    With $(2)... "; \
+	cp tb_data/$(2).time $(TEST_OUTDIR); \
+	for e in $(3); do cp tb_data/$(2).$$e $(TEST_OUTDIR)/data.$$e; done; \
+	./$(1)