Out of tree build

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:

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

Overriding in-tree headers

If you need to override a header that lives inside the main firmware tree (for example to tweak the PID gains or physical constants in platform_defaults_cf2.h for your build, without editing the in-tree file), place your replacement in an overrides folder next to your OOT Makefile. $(OOT)/overrides is searched before every other include path, so a file placed there is picked up instead of its in-tree namesake, for the whole firmware build — not just your own OOT sources.

This only works for a header that is #included (with quotes) from a file outside the directory the header itself lives in — the C preprocessor always checks the includer’s own directory first, before any -I path, so a header included by a neighbour in the same directory can never be shadowed this way.

platform_defaults_cf2.h (and its sibling platform headers) is not directly shadowable by this rule: it’s only ever included from platform_defaults.h, which lives right next to it in src/platform/interface. Overriding it therefore requires overriding both files together:

your_oot_folder/
├── Makefile
├── overrides/
│   ├── platform_defaults.h        # unmodified copy of the in-tree file
│   └── platform_defaults_cf2.h    # your changes go here
└── ...

platform_defaults.h itself is directly shadowable, since it’s included from files spread across src/hal, src/drivers, src/modules, etc. — none of which live in src/platform/interface. Once your copy of it is the one being compiled, its own #include "platform_defaults_cf2.h" resolves relative to its location (overrides/), which is what lets your copy of platform_defaults_cf2.h be found in turn.

OOT builds can be configured with Kbuild using terminal interfaces like make menuconfig or by loading a default configuration, such as with make cf2_defconfig. Any definitions in $(OOT_CONFIG) will override conflicting settings.

Note: If you are using macOS you may encounter errors when trying to build your app, such as:

readlink: illegal option -- m
sed: invalid command code .
cp: illegal option -- T

This happens because the app-layer build expects the GNU versions of readlink, sed and cp. To fix the errors, install and use the GNU utilities:

brew install coreutils gnu-sed

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.