make Makefile-{SIM,AVR,common} more generic

Allow stock makefile variables to be overridden by 'make' caller
so the user's 'Makefile' can be authoritative.

See Makefile-example for usage.

Makefile-AVR

@@ -40,17 +40,17 @@
 #                                                                            #
 ##############################################################################
 
-# MCU_TARGET = atmega168
-# MCU_TARGET = atmega328p
-MCU_TARGET = atmega644p
-# MCU_TARGET = atmega1280
-# MCU_TARGET = atmega2560
-# MCU_TARGET = at90usb1287
-# MCU_TARGET = atmega32u4
+# MCU_TARGET ?= atmega168
+# MCU_TARGET ?= atmega328p
+MCU_TARGET ?= atmega644p
+# MCU_TARGET ?= atmega1280
+# MCU_TARGET ?= atmega2560
+# MCU_TARGET ?= at90usb1287
+# MCU_TARGET ?= atmega32u4
 
 # CPU clock rate
-F_CPU = 16000000L
-# F_CPU = 8000000L
+F_CPU ?= 16000000L
+# F_CPU ?= 8000000L
 
 ##############################################################################
 #                                                                            #
@@ -79,9 +79,10 @@ TOOLCHAIN = avr-
 #   -P <port>                 Serial port the electronics is connected to.
 #   -C <config file>          Optional, default is /etc/avrdude.conf.
 
-UPLOADER = avrdude
+UPLOADER ?= avrdude
 # UPLOADER = <path-to-arduino-folder>/hardware/tools/avrdude
 
+ifndef UPLOADER_FLAGS
 UPLOADER_FLAGS  = -c stk500v2
 # UPLOADER_FLAGS += -b 19200
 # UPLOADER_FLAGS += -b 57600
@@ -91,6 +92,7 @@ UPLOADER_FLAGS += -p $(MCU_TARGET)
 # UPLOADER_FLAGS += -P /dev/ttyACM0
 UPLOADER_FLAGS += -P /dev/ttyUSB0
 # UPLOADER_FLAGS += -C <path-to-arduino-folder>/hardware/tools/avrdude.conf
+endif
 
 
 ##############################################################################
@@ -108,7 +110,7 @@ TARGET = $(PROGRAM).hex
 # to keep this working and can take a shortcut:
 SOURCES = $(wildcard *.c)
 
-CFLAGS  = -DF_CPU=$(F_CPU)
+CFLAGS += -DF_CPU=$(F_CPU)
 CFLAGS += -mmcu=$(MCU_TARGET)
 CFLAGS += -g
 CFLAGS += -Wall

Makefile-SIM

@@ -44,7 +44,7 @@ SIM_SOURCES = $(subst $(SIM_PATH)/,,$(wildcard $(SIM_PATH)/*.c))
 SOURCES := $(filter-out $(subst _sim.c,.c,$(SIM_SOURCES)),$(SOURCES)) $(SIM_SOURCES)
 
 OBJ = $(patsubst %.c,$(BUILDDIR)/%.sim.o,$(SOURCES))
-CFLAGS  = -g -Wall -Wstrict-prototypes -Wno-format -Os $(DEFS) -std=gnu99
+CFLAGS += -g -Wall -Wstrict-prototypes -Wno-format -Os $(DEFS) -std=gnu99
 CFLAGS += -funsigned-char -funsigned-bitfields -fshort-enums -I.. -I.
 CFLAGS += -DSIMULATOR
 

Makefile-example

@@ -0,0 +1,36 @@
+################################################################################
+#
+## Example Makefile
+#
+# For convenience, copy this file to "Makefile" and customize it to fit your
+# needs.
+#
+# Then you can type 'make avr' or simply 'make' to build for your printer.
+#
+################################################################################
+.PHONY: sim avr clean all default
+
+# Override variables in the stock makefiles
+export F_CPU = 20000000L
+export MCU_TARGET = atmega644p
+
+default: avr
+
+all: sim avr
+
+# Build the simulator
+sim:
+	@echo "----[ Simulator ]----"
+	@make -sf Makefile-SIM
+
+# Build Teacup for an Atmel processor
+avr:
+	@echo "----[ $(MCU_TARGET) ]----"
+	@make -sf Makefile-AVR
+
+clean:
+	@echo "----[ Clean ]----"
+	@make -sf Makefile-SIM clean
+	@make -sf Makefile-AVR clean
+	# Add any more cleanup steps you want here. Example,
+	# rm -f *.png