Building NuttX with Applications Outside of the Source Tree

Q: Has anyone come up with a tidy way to build NuttX with board-specific pieces outside the source tree?

A: Here are three:

1. Make export

There is a make target called make export. It will build NuttX, then bundle all of the header files, libaries, startup objects, and other build components into a .zip file. You can can move that .zip file into any build environment you want. You even build NuttX under a DOS CMD window.

This make target is documented in the top level nuttx/README.txt.

2. Replace the apps/ Directory

You can replace the entire apps/ directory. It is not a critical part of the OS. The apps/ is simply provided for you to help with your application development. It should not dictate anything that that you do.

To use a different apps directory, simply execute make menuconfig in the top-level nuttx/ directory and redefine CONFIG_APPS_DIR in your .config file so that it points to a different, custom application directory. Note that CONFIG_APPS_DIR is a relative path from the top-level nuttx/ directory.

You can copy any pieces that you like from the old apps/directory to your custom apps directory as necessary. This is documented in nuttx/configs/README.txt, in the NuttX Porting Guide and Build options, and in the apps/README.txt file.

3. Extend the apps/ Directory

If you like the random collection of stuff in the apps/ directory but just want to expand the existing components with your own, external sub-directory then there is an easy way to that too: You just create a sympolic link in the apps/ directory that redirects to your application sub-directory (or copy your code into a sub-directory of apps/).

In order to be incorporated into the build, the directory that you link under the apps/ directory should contain (1) a Makefile that supports the clean and distclean targets (see other Makefiles for examples), and (2) a tiny Make.defs make file fragment that simply adds the build directories to the variable CONFIGURED_APPS like:

CONFIGURED_APPS += my_directory1 my_directory2

The apps/Makefile will always automatically check for the existence of subdirectories containing a Makefile and a Make.defsfile. The Makefile will be used only to support cleaning operations. The Make.defs file provides the set of relative pathes to directories to be built; these directories must also contain a Makefile. That Makefile that can build the sources and add the object files to apps/libapps.a archive (see other Makefiles for examples). It should support the all, install, context, and depend targets.

apps/Makefile does not depend on any hardcoded lists of directories. Instead, it does a wildcard search to find all appropriate directories. This means that to install a new application, you simply have to copy the directory (or link it) into the apps/ directory. If the new directory includes a Makefile and a Make.defs file, then it will be automatically discovered and included in the build at make time.

If the directory that you add also includes a Kconfig file, then it will automatically be included in the NuttX configuration system as well. apps/Makefile uses a tool at apps/tools/ that dynamically builds the apps/Kconfig file at pre-configuration time.

NOTE: The native Windows build is will use a corresponding tool called apps/tools/mkconfig.bat.

You could, for example, create a script called that installs a custom application, configuration, and board specific directory:

  • Copy MyBoard directory to configs/MyBoard.
  • Add a symbolic link to MyApplication at apps/external
  • Configure NuttX:
tools/ MyBoard/MyConfiguration

Use of the name apps/external is suggested because that name is included in the .gitignore file and will save you some nuisance when working with GIT.

Hooking External Applications into the Configuration System

Suppose you would also like to support configuration variables in your external application. No problem. Thanks to Sebastien Lorquet, any external application that you install into the apps/, whether via a symbolic link or via a directory copy, will be included into the NuttX configuration system.

The top-level Kconfig file in the apps/ directory is automatically generated based on the contents of each apps/ sub-directory. If your installed sub-directory contains, Kconfig, Makefile, and Make.defs files, then it will be incorporated into the NuttX configuration system when the top-level Kconfig file is generated.