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IoT Reference OS Kit for Intel(r) Architecture Introduction

IoT Reference OS Kit for Intel(r) Architecture (The Reference Kit) is a new set of Yocto Project metadata layers and infrastructure geared towards IoT development. The Reference Kit is a preconfigured Yocto Project based platform that is easy to take in use and customize further.

The Reference Kit introduces the concept of a "profile" - an image configuration that demonstrates certain key IoT usage. Examples of planned profiles are industrial, gateway and computer vision, but others could be included.

Each profile is defined in its own, self-contained layer. Each layer defines which other layers it depends on, both in the README.rst (for humans) and in the layer.conf (for tools like the layer index and Toaster).

The Reference Kit repository is built such that it integrates selected Yocto Project layers together and ensures that the content works seamlessly together. All external layers get imported as git submodules, using a revision that is known to work. Run :command:`git ls-tree HEAD | grep " commit "` in the intel-iot-refkit repository to get the exact revision of each subcomponent that is used.

By default the Reference Kit runs on Intel's meta-intel BSP platforms.

The Yocto Project extensible software development kit (eSDK) is comes pre-configured and pre-tested in Reference Kit repository but the users of it must build the SDK installer themselves. By default, the eSDK type is "minimal" which implies at least the SSTATE_MIRROR setting must be adjusted when building distributable eSDKs. For more documentation on how to customize and re-configure the eSDK, see the "Appendig B. Customizing the Extensible SDK" in the Yocto Project extensible software development kit manual.

The Reference kit follows the Yocto Project release cadence, keeps the content in the Yocto Project git and uses the Yocto Project Bugzilla for feature and bug tracking.

Layer Overview and Reuse

Layers

IoT Reference OS Kit supports using its layers also in other projects without using the Reference Kit distribution. Each layer is "Yocto Compatible 2.0", which guarantees that merely adding it to a build configuration does not change the build unless explicitly requested (for example, in local.conf, distro configurations, or image recipes).

Some of the content may depend on specific distribution configuration options. For specific usage instructions, see :file:`profiles.rst`.

Another caveat is that obviously not all combinations can be tested exhaustively. What gets tested is that each individual layer can be added to the Poky Yocto Project reference distribution and that they do not break a world build.

Full testing of features only happens on the refkit distribution itself, so that is the recommended starting point for someone who wants to try out something.

The intel-iot-refkit repository contains the following layers:

meta-refkit
The distribution layer. Depends on all other layers.
meta-refkit-extra
Demos that run on top of the Reference Kit distribution and thus depends on meta-refkit.
meta-refkit-core
Common utility classes and miscellaneous recipes which are not profile-specific. The only hard dependency of this layer is openembedded-core. :file:`meta-refkit-core/conf/layer.conf` automatically detects available layers and enables content based on that. When providing recipes via some other layer, override the HAVE_... variables from that :file:`layer.conf`. For example, the dm-verity support depends on cryptsetup, which could be provided either by adding meta-security or copying the recipe into a distro-specific layer. In the latter case, HAVE_CRYPTSETUP has to be set.
meta-refkit-computervision/gateway/...
Profile layers. See also :file:`profiles.rst`.

Note that meta-<something> is the directory containing the layer called <something>, although in practice meta-<something> and "the <something> layer" are often used interchangeably.

Common Features

The reusable part of the distro configuration (package configuration, default distro features, etc.) is made available to other distros via :file:`meta-refkit-core/conf/distro/include/refkit-config.inc`.

To reuse the distro configuration in addition to the layer content:

  • Add require "conf/distro/include/refkit-config.inc", and
  • use enable same distro features as the refkit distro (in particular, systemd) with require "conf/distro/include/enable-refkit-config.inc,
  • or choose individual distro features to match your needs.

These changes can go into file:local.conf or a custom distro configuration file.

See file:refkit-config.inc for a description of the currently supported special distro features.

Supported Recipes

The Reference Kit distribution uses supported-recipes.bbclass to control which recipes are part of the distribution. It uses explicit, complete lists of recipes that are part of a project and thus is easier to review and maintain. Accidentally pulling in additional content triggers a warning or error (depending on the configuration) which explains the dependency that pulled in the content.

For example, although several layers from meta-openembedded are required for a build, only a well-chosen and tested subset of it is really needed. The rest will not be part of a bitbake world build either.

This mechanism is completely optional. The individual layers do not track the recipes that they need, only the refkit distro layer and its refkit-extra add-on layer have such a list in :file:`meta-refkit/conf/distro/include/refkit-supported-recipes.txt` and :file:`meta-refkit-extra/conf/distro/include/refkit-extra-supported-recipes.txt`.

Projects which want to use the same mechanism can do so via their distro or local configuration, similar to how :file:`refkit.conf` in meta-refkit does it.

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