zephyr/doc/guides/west/why.rst

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.. _west-history:
History and Motivation
######################
West was added to the Zephyr project to fulfill two fundamental requirements:
* The ability to work with multiple Git repositories
* The ability to provide a user-friendly command-line interface to the Zephyr
build system and debug mechanisms
Additionally, it was desired that west be easily extensible by
downstream users.
During the development of west, a set of :ref:`west-design-constraints` were
identified to avoid the common pitfalls of tools of this kind.
Multiple Git Repositories
*************************
Zephyr intends to provide all required building blocks needed to deploy complex
IoT applications. This in turn means that the Zephyr project is much more than
an RTOS kernel, and is instead a collection of components that work together.
In this context, there are a few reasons to work with multiple Git
repositories in a standardized manner within the project:
* Clean separation of Zephyr original code and imported projects and libraries
* Avoidance of license incompatibilities between original and imported code
* Reduction in size and scope of the core Zephyr codebase, with additional
repositories containing optional components instead of being imported
directly into the tree
* Safety and security certifications
* Enforcement of modularization of the components
* Out-of-tree development based on subsets of the supported boards and SoCs
See :ref:`west-multi-repo` for a detailed explanation of west's handling of
multiple repository management.
.. _west-design-constraints:
Design Constraints
******************
West is:
- **Optional**: it is always *possible* to drop back to "raw"
command-line tools, i.e. use Zephyr without using west (although west itself
might need to be installed and accessible to the build system). It may not
always be *convenient* to do so, however. (If all of west's features
were already conveniently available, there would be no reason to
develop it.)
- **Compatible with CMake**: building, flashing and debugging, and
emulator support will always remain compatible with direct use of
CMake.
- **Cross-platform**: West is written in Python 3, and works on all
platforms supported by Zephyr.
- **Usable as a Library**: whenever possible, west features are
implemented as libraries that can be used standalone in other
programs, along with separate command line interfaces that wrap
them. West itself is a Python package named ``west``; its libraries
are implemented as subpackages.
- **Conservative about features**: no features will be accepted without
strong and compelling motivation.
- **Clearly specified**: West's behavior in cases where it wraps other
commands is clearly specified and documented. This enables
interoperability with third party tools, and means Zephyr developers
can always find out what is happening "under the hood" when using west.
See `Zephyr issue #6205`_ and for more details and discussion.
.. _Zephyr issue #6205:
https://github.com/zephyrproject-rtos/zephyr/issues/6205