diff --git a/vhdl/Makefile b/vhdl/Makefile
index 0f5e60f..d938530 100644
--- a/vhdl/Makefile
+++ b/vhdl/Makefile
@@ -2,14 +2,27 @@ DESIGN     := risc_v
 DESIGN_SRC := risc_v_pkg.vhd risc_v.vhd
 TESTBENCH  := tb_${DESIGN}
 
-.PHONY: sim
-sim: tb_${DESIGN}.ghw
+DEFAULT: sim
 
-${TESTBENCH}.ghw : ${DESIGN_SRC} ${TESTBENCH}.vhd
+${TESTBENCH} : ${DESIGN_SRC} ${TESTBENCH}.vhd
 	ghdl -a --std=08 ${DESIGN_SRC} ${TESTBENCH}.vhd
 	ghdl -e --std=08 ${TESTBENCH}
-	ghdl -r --std=08 ${TESTBENCH} --vcd=${TESTBENCH}.vcd --wave=$@
+
+.PHONY: sim
+sim: ${TESTBENCH}.ghw
+
+ ${TESTBENCH}.ghw: ${TESTBENCH}
+	ghdl -r --std=08 ${TESTBENCH} --ieee-asserts=disable-at-0 --vcd=${TESTBENCH}.vcd --wave=$@
+
+.PHONY: syn
+syn: $(DESIGN).json
+
+$(DESIGN).o: $(DESIGN_SRC)
+	ghdl -a --std=08 $(DESIGN_SRC)
+
+$(DESIGN).json: $(DESIGN).o
+	yosys -m ghdl -p 'ghdl --std=08 --no-formal ${DESIGN}; synth_ice40 -json $@'
 
 .PHONY: clean
 clean:
-	rm ${TESTBENCH} ${TESTBENCH}.ghw ${TESTBENCH}.vcd work* *.o
+	rm -f ${TESTBENCH} ${TESTBENCH}.ghw ${TESTBENCH}.vcd work* *.o *.json