diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..25d783d
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "verilog-lfsr"]
+	path = lib/verilog-lfsr
+	url = ../verilog-lfsr.git
diff --git a/LICENSES/MIT.txt b/LICENSES/MIT.txt
new file mode 100644
index 0000000..1b8f1ce
--- /dev/null
+++ b/LICENSES/MIT.txt
@@ -0,0 +1,19 @@
+Copyright (c) 2016 Alex Forencich
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/Makefile b/Makefile
index eceb588..9e689ff 100644
--- a/Makefile
+++ b/Makefile
@@ -18,8 +18,13 @@ FORCE:
 log:
 	mkdir $@
 
+LIBDIRS := rtl lib/verilog-lfsr/rtl
 %.synth.json: %.v | log
-	$(SYNTH) -q -E $@.d -p "synth_ice40 -top $(*F)" -b json -o $@ -f verilog $< -l log/$(*F).synth
+	( \
+		echo "read_verilog -sv $<"; \
+		echo "hierarchy $(addprefix -libdir ,$(LIBDIRS) $(<D))"; \
+		echo "synth_ice40 -top $(*F)"; \
+	) | $(SYNTH) -q -E $@.d -s /dev/stdin -b json -o $@ -l log/$(*F).synth
 
 define run-jsontov =
 	( grep timescale $*.v; $(SYNTH) -q -p "write_verilog -defparam -noattr" -f json $< ) > $@
@@ -36,7 +41,8 @@ IFLAGS := -g2012 -gspecify -Wall -Wno-timescale
 EXTRA_V := rtl/iverilog_dump.v
 
 define run-icarus =
-$(ICARUS) $(IFLAGS) -I$(<D) -y$(<D) -M$@.pre -DTOP=$(TOP) -s $(TOP) -s iverilog_dump -o $@ $< $(EXTRA_V) && \
+$(ICARUS) $(IFLAGS) -I$(<D) $(addprefix -y,$(LIBDIRS) $(<D)) -M$@.pre -DTOP=$(TOP) \
+	-s $(TOP) -s iverilog_dump -o $@ $< $(EXTRA_V) && \
 	( echo -n "$@: " && tr '\n' ' ' ) < $@.pre > $@.d; RET=$$?; rm -f $@.pre; exit $$RET
 endef
 
diff --git a/lib/verilog-lfsr b/lib/verilog-lfsr
new file mode 160000
index 0000000..2ae88c6
--- /dev/null
+++ b/lib/verilog-lfsr
@@ -0,0 +1 @@
+Subproject commit 2ae88c6953d7434411c0f90f9f09e78c2361a6ad