+# Sanity check user supplied values
+$(foreach MANDATORY_VAR, $(LUFA_BUILD_MANDATORY_VARS), $(call ERROR_IF_UNSET, $(MANDATORY_VAR)))
+$(call ERROR_IF_EMPTY, MCU)
+$(call ERROR_IF_EMPTY, TARGET)
+$(call ERROR_IF_EMPTY, ARCH)
+$(call ERROR_IF_EMPTY, F_USB)
+$(call ERROR_IF_EMPTY, LUFA_PATH)
+$(call ERROR_IF_EMPTY, BOARD)
+$(call ERROR_IF_EMPTY, OPTIMIZATION)
+$(call ERROR_IF_EMPTY, C_STANDARD)
+$(call ERROR_IF_EMPTY, CPP_STANDARD)
+