It is possible to have an out-of-tree build of parts of the crazyflie firmware. This enables developers to work on elements without worrying about merging it with the full code base.

General out-of-tree build process

In a separate folder create a Makefile which contain the following content:

CRAZYFLIE_BASE := [LOCATION OF THE CRAZYFLIE FIRMWARE]

#
# We override the default OOT_CONFIG here, we could also name our config
# to oot-config and that would be the default.
#
OOT_CONFIG := $(PWD)/config

include $(CRAZYFLIE_BASE)/tools/make/oot.mk

This will make the crazyflie-firmware build system look for a Kbuild file in your folder.

The following variables are understood by oot.mk:

Variable	Function	Default
`OOT`	Specify where your code (`Kbuild file`) is located.	`$(PWD)` (Your current directory)
`OOT_CONFIG`	Location of your OOT specific `Kconfig` file, will be merged with the default config.	`$(OOT)/oot-config`
`EXTRA_CFLAGS`	Extra CFLAGS needed by your app	Empty.

And oot.mk also expects $(CRAZYFLIE_BASE) to be set to the path to the crazyflie-firmware repository.

The Kbuild file in the $(OOT) folder should point out your source files:

obj-y += your_estimator_out_of_tree.o

It can also point out another folder where the code resides:

obj-y += src/

If you have header files in another folder, use EXTRA_CFLAGS in the Makefile to let the compiler know where to find them:

EXTRA_CFLAGS += -I$(PWD)/src/inc

And since you are providing a config file by way of $(OOT_CONFIG) you do not need to run any make command to create a config like make menuconfig or make defconfig. Just a simple make will suffice.

OOT estimators

The config file needs to enable ESTIMATOR_OOT, and can also set other config options:

CONFIG_ESTIMATOR_OOT=y

in [your_estimator_out_of_tree].c in the src folder you will just need to make sure that the following functions are implemented:

init = estimatorOutOfTreeInit
test = estimatorOutOfTreeTest
update = estimatorOutOfTree

OOT Controllers

The config file needs to enable CONTROLLER_OOT, and can also set other config options:

CONFIG_CONTROLLER_OOT=y

in [your_controller_out_of_tree].c in the src folder you will just need to make sure that the following functions are implemented:

init = controllerOutOfTreeInit
test = controllerOutOfTreeTest
update = controllerOutOfTree

App layer

Technically the app layer is an example of an out of tree build. Follow the app layer instructions for this.