Current versions of OpenEmbedded are based on OpenEmbedded-Core (OE-Core). OE-Core has evolved from collaboration efforts with the Yocto Project as well as a recognition that the model previously being used in OpenEmbedded was unsustainable.
The original OpenEmbedded repository (also known as "OE-Classic" or "oe-dev") has grown organically over the years to more than 7500 recipes, covering approximately 300 machines and 20 distros. Trying to maintain this amount of metadata with machine and distro overrides scattered throughout is very difficult, and near to impossible to support commercially. Like many other OE forks that have been created to solve the same kinds of issues, Poky was forked as a cleaner and more supportable version of OE in 2006. Fast forwarding to the present, Poky is now maintained as a reference distribution under the Yocto Project with the support of the Linux Foundation. OE-Core was split out from Poky in 2011 to allow collaboration around a relatively small and easily supportable base, with real machines, distros and other items removed - more on this below.
Apart from the 2011.3-maintenance branch which is preserved for existing projects, OE-Classic is no longer maintained. New efforts should be built on top of OE-Core. The new OE layer ecosystem provides full support for building typical embedded Linux systems, support for many target machines and additional software packages. Some recipes and machine support has yet to be ported over from OE classic, however recipes and configuration can be easily brought over, tidied up and placed into the appropriate layer over time.
Differences to OE-classic
The most significant change is that metadata is now split into multiple layers rather than being in one repository. OE-Core sits at the bottom, and machine / application / distro layers are added on top. Users are free to select support for whatever applications or platforms they wish in their configuration simply by including the appropriate layer in their bblayers.conf file.
Machine and distro-specific overrides should no longer be spread over the entire set of recipes - instead they should be concentrated in appropriate machine support layers (often referred to as BSP (Board Support Package) layers) and distro layers respectively. BitBake's .bbappend feature allows overriding almost any element of a recipe without too much duplication across multiple layers.
Additionally, OE-Core moves changes to a pull model rather than the push model of OE-classic - instead of all developers having direct commit access, patches are sent to the mailing list for review and if/when satisfactory they are merged by the maintainer. Other layers may choose to use either the push or pull model for contributions.
The scope of OE-Core is as follows:
- Support for five architectures: ARM, x86, x86-64, PowerPC and MIPS
- Only QEMU emulated machines
- Distro-less (DISTRO = "" and default values are used)
- Only one X-based GUI environment (Sato) intended for testing purposes. (This may be substituted out in future if a suitable replacement testing framework can be created.)
- Only the recipes that are needed by almost everyone, needed for LSB support (optional) or are needed for testing other parts of OE-Core
- Attempt to keep only one version of each recipe except for GPLv2 / v3 versions
Anything not in OE-Core can easily be provided by another layer; other layers can also be used to support older versions that have been removed from OE-Core.
For items shared amongst multiple layers that do not fit into OE-Core or any other existing layer, there is the meta-oe layer. This exists in a repository, also called meta-openembedded, which contains a number of other more focused layers (meta-efl, meta-gnome, etc.). This layer will need to be managed carefully over time to avoid it turning into just a newer version of OE-classic.
See Getting started.
OpenEmbedded maintains an list of layers that can be used with OE-Core - see the layer index.
See Creating a new Layer.