====== Introduction to Yocto/OpenEmbedded ======

[[https://www.yoctoproject.org/ | yocto]] and [[https://www.openembedded.org/wiki/Main_Page | OpenEmbedded]] provide the tools necessary to create small customised linux distributions aimed at embedded systems.


===== yocto, OpenEmbedded, bitbake and poky =====

When dealing with this ecosystem there are a number of terms to be aware of:

**OpenEmbedded** maintains a build environment and cross-compile environment to build linux.
The **yocto** project uses OpenEmbedded to provide a framework to create repeatable custom linux distributions and images.
Yocto includes a reference distribution called **poky** as a starting point for customisation.
Poky encompasses everything needed to boot to a shell prompt and most of the typical posix command line tools (as provided by [[https://busybox.net/ | busybox]]).
The build system used by yocto (from OpenEmbedded) is called **bitbake**. Bitbake uses the notions of recipes organised into layers to organise its builds.

===== bitbake =====

Bitbake is the build system used by yocto and OpenEmbedded.

===== Recipes =====
Rather than defining all parts of the build in a single file (like make or cmake), bitbake separates each component that needs to be built into its own file.
This file is that component's recipe.
Each recipe can either provide one or more packages (for example, libraries will often provide a lib and lib-dev package), or modify an existing recipe.
The latter is useful when the package you want to modify is not under your control.
Whether a file represents a new recipe or changes to an existing one is controlled by its file extension: files for new recipes end in ''.bb'' while those modifying existing recipes end in ''.bbappend''.

Check the [[ .:recipes | Recipes ]] page for more information.

===== Layers =====

Groups of recipes that belong together are grouped into layers.
For example [[.:meta-ost | meta-ost]] is the layer that contains all the things we need in our images. Some repositories are named after layers. They typically contain a collection of associated layers.
''meta-openembedded'' is such a collection.
It contains various programs split into layers such as ''meta-connectivity'' and ''meta-python''.
Note that in such cases you need to add each layer in the repository separately (e.g. ''meta-openembedded/meta-connectivity'' rather than ''meta-openembedded'').
See also: [[ .:setup |Setting up the Build Environment ]]


Check the [[ .:layer | Layer ]] page for more information.

==== BSP ====

The BSP (board support package) is just a layer that provides a bootloader and kernel specific to the hardware that the BSP is for. 

==== Machines ====

Machines are bitbake's way of managing harware specific settings.
Machines are defined in ''<layer-name>/conf/machine/<machine-name>.conf''.
This is the place to set machine specific configurations such as the kernel provider.

See also: [[.:layer | Layers]]

===== Kernel Development =====

See [[ .:kernel | Kernel ]]