-ifeq ($(TARGET),)\r
- $(error Makefile TARGET value not set.)\r
-endif\r
-ifeq ($(ARCH),)\r
- $(error Makefile ARCH value not set.)\r
-endif\r
-ifeq ($(MCU),)\r
- $(error Makefile MCU value not set.)\r
-endif\r
-ifeq ($(SRC),)\r
- $(error Makefile SRC value not set.)\r
-endif\r
-ifeq ($(F_USB),)\r
- $(error Makefile F_USB value not set.)\r
-endif\r
-ifeq ($(LUFA_PATH),)\r
- $(error Makefile LUFA_PATH value not set.)\r
-endif\r
+MCU ?= $(error Makefile MCU value not set.)\r
+TARGET ?= $(error Makefile TARGET value not set.)\r
+ARCH ?= $(error Makefile ARCH value not set.)\r
+SRC ?= $(error Makefile SRC value not set.)\r
+F_USB ?= $(error Makefile F_USB value not set.)\r
+LUFA_PATH ?= $(error Makefile LUFA_PATH value not set.)\r