add usage & tests

Makefile

@@ -7,7 +7,20 @@ export TARGET
 
 
 default:
-	echo "TODO"
+	@echo "Usage"
+	@echo "  test:     run tests, use TEST=test_name specify test folder in tests, default test all tests"
+	@echo "  uftb:     build uFTB DUT module"
+	@echo "  tage_sc:  build TAGE_SC DUT module"
+	@echo "  ftb:      build FTB DUT module"
+	@echo "  ras:      build RAS DUT module"
+	@echo "  ittage:   build ITTAGE DUT module"
+	@echo "  all:      build all DUTs"
+	@echo "Make examples:"
+	@echo "  make test TEST=uFTB-raw"
+	@echo "  make uftb"
+
+test:
+	make -f tests/Makefile
 
 uftb:
 	make -f ./mk/uFTB.mk uftb