-DEFS = -D$(call uc, $(MCU_TARGET))
-FLASHCMD = avrdude -p $(MCU_TARGET) -P /dev/ttyUSB0 -c $(PROGRAMMER) -U flash:w:# no space at the end
+PROG_PORT = /dev/ttyUSB0
+DEFS = -D$(call uc, $(MCU_TARGET)) -DF_CPU=$(F_CPU)
+FLASHCMD = avrdude -p $(MCU_TARGET) -P $(PROG_PORT) -c $(PROGRAMMER) -U flash:w:# no space at the end