esp-idf/components/bootloader/Makefile.projbuild

#
# Bootloader component
#
# The bootloader is not a real component that gets linked into the project.
# Instead it is an entire standalone project ( in src/) that gets built in 
# the upper projects build directory. This Makefile.projbuild provides the 
# glue to  build the bootloader project from the original project. It 
# basically runs Make in the src/ directory but it needs to zero some variables
# the ESP-IDF project.mk makefile exports first, to not let them interfere.
#
ifeq ("$(IS_BOOTLOADER_BUILD)","")

BOOTLOADER_COMPONENT_PATH := $(COMPONENT_PATH)
BOOTLOADER_BUILD_DIR=$(BUILD_DIR_BASE)/bootloader
BOOTLOADER_BIN=$(BOOTLOADER_BUILD_DIR)/bootloader.bin

.PHONY: bootloader-clean bootloader-flash bootloader $(BOOTLOADER_BIN)

$(BOOTLOADER_BIN): $(COMPONENT_PATH)/src/sdkconfig
	$(Q) PROJECT_PATH= \
	BUILD_DIR_BASE=$(BOOTLOADER_BUILD_DIR) \
	$(MAKE) -C $(BOOTLOADER_COMPONENT_PATH)/src MAKEFLAGS= V=$(V) TARGET_BIN_LAYOUT="$(BOOTLOADER_TARGET_BIN_LAYOUT)" $(BOOTLOADER_BIN)

bootloader-clean:
	$(Q) PROJECT_PATH= \
	BUILD_DIR_BASE=$(BOOTLOADER_BUILD_DIR) \
	$(MAKE) -C $(BOOTLOADER_COMPONENT_PATH)/src app-clean MAKEFLAGS= V=$(V)

clean: bootloader-clean

bootloader: $(BOOTLOADER_BIN)
	@echo "Bootloader built. Default flash command is:"
	@echo "$(ESPTOOLPY_WRITE_FLASH) 0x1000 $(BOOTLOADER_BIN)"

all_binaries: $(BOOTLOADER_BIN)

ESPTOOL_ALL_FLASH_ARGS += 0x1000 $(BOOTLOADER_BIN)

# synchronise the project level config to the component's
# config
$(COMPONENT_PATH)/src/sdkconfig: $(PROJECT_PATH)/sdkconfig
	$(Q) cp $< $@

# bootloader-flash calls flash in the bootloader dummy project
bootloader-flash: $(BOOTLOADER_BIN)
	$(MAKE) -C $(BOOTLOADER_COMPONENT_PATH)/src flash MAKEFLAGS= V=$(V)

else
CFLAGS += -D BOOTLOADER_BUILD=1 -I $(IDF_PATH)/components/esp32/include 

endif