makefile

# Compiler
CC := arm-none-eabi-gcc
AS := arm-none-eabi-as

# Targets
TARGET_NAME := gps_time
BUILDPREFIX := build/
SOURCEPREFIX := sources/
SOURCES += $(SOURCEPREFIX)main.c \
           $(SOURCEPREFIX)start.c
ASM_SOURCES += $(SOURCEPREFIX)gcc_startup.s

# Primary output target is elf
TARGETS := $(BUILDPREFIX)$(TARGET_NAME).elf
TARGETS += $(BUILDPREFIX)$(TARGET_NAME).hex

# Linker
LDSCRIPT := gcc_nrf51822_gpstime.ld
LDFLAGS := -Wl,--gc-sections

# Initialize compiler flags to empty
CFLAGS :=

# Include paths
CMSIS_PATH := $(SOURCEPREFIX)cmsis/

# Compiler paths
CFLAGS += -Wall -std=gnu99 -mthumb -ggdb -Os -ffunction-sections -fdata-sections
CFLAGS += -Werror -lnosys -lgcc --specs=nano.specs -nostartfiles
CFLAGS += -mcpu=cortex-m0 -DARM_MATH_CM0
ASMFLAGS := $(CFLAGS) -x assembler-with-cpp

# Include all subdir makefiles
include $(SOURCEPREFIX)makefile

CFLAGS += -I$(CMSIS_PATH)

# must escape quotes for echo to work
ESCAPED_FLAGS := $(subst ",\",$(CFLAGS))

# Generate object file names and add source and build path prefixes.
OBJECTS := $(patsubst $(SOURCEPREFIX)%,                         \
                      $(BUILDPREFIX)%,                          \
                      $(patsubst *.S,*.o,$(ASM_SOURCES:.s=.o))  \
                      $(SOURCES:.c=.o) $(SYSLIBSOURCES:.c=.o))
           
define BUILD_HEX_FILE
    echo "Converting $(2) -> $(1)"
    arm-none-eabi-objcopy $(2) -O ihex $(1)
endef

define LINK
	echo "  Linking $(1)"
	$(CC) $(CFLAGS) $(LDFLAGS) -o $(1) $(2) \
	      -Wl,-Map,$(patsubst %.elf,%.map,$(1)) \
	      -Wl,-T,$(LDSCRIPT)
endef

define COMPILE
	echo "  CC $(2) $(ESCAPED_FLAGS)"
	mkdir -p $(dir $(1))
	$(CC) $(CFLAGS) -c -o $(1) $(2) -MMD -MF $(1:.o=.d)
endef

define COMPILE_ASM
	echo "  AS $(2) $(ESCAPED_FLAGS)"
	mkdir -p $(dir $(1))
	$(CC) $(ASMFLAGS) -c -o $(1) $(2) -MMD -MF $(1:.o=.d)
endef

define CLEAN
	$(RM) $(TARGETS) $(OBJECTS) $(AUTODEPS) \
	$(patsubst %.elf,%.map,$(filter %.elf,$(TARGETS)))
endef

# Use dependency files automatically generated by GCC.
# First collect all C source files
AUTODEPS := $(patsubst $(SOURCEPREFIX)%.c, $(BUILDPREFIX)%.d, $(SOURCES))
# And then add the asm source files
AUTODEPS := $(patsubst $(SOURCEPREFIX)%.s, $(BUILDPREFIX)%.d, \
            $(patsubst $(SOURCEPREFIX)%.S, $(BUILDPREFIX)%.d, \
            $(AUTODEPS) $(ASM_SOURCES)))

.SILENT:

.PHONY: all
all: $(TARGETS)

.PHONY: clean
clean:
	$(call CLEAN)

$(BUILDPREFIX)$(TARGET_NAME).elf: $(OBJECTS)
	$(call LINK,$@,$^)
	
%.hex: %.elf
	$(call BUILD_HEX_FILE,$@,$<)

$(BUILDPREFIX)%.o: $(SOURCEPREFIX)%.c
	$(call COMPILE,$@,$<)

$(BUILDPREFIX)%.o: $(SOURCEPREFIX)%.s
	$(call COMPILE_ASM,$@,$<)

-include $(AUTODEPS)