In the
general Yocto Project Development Environment figure,
the output labeled "Application Development SDK" represents an
SDK.
The SDK generation process differs depending on whether you build
a standard SDK
(e.g. bitbake -c populate_sdk imagename)
or an extensible SDK
(e.g. bitbake -c populate_sdk_ext imagename).
This section is going to take a closer look at this output:
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The specific form of this output is a self-extracting
SDK installer (*.sh) that, when run,
installs the SDK, which consists of a cross-development
toolchain, a set of libraries and headers, and an SDK
environment setup script.
Running this installer essentially sets up your
cross-development environment.
You can think of the cross-toolchain as the "host"
part because it runs on the SDK machine.
You can think of the libraries and headers as the "target"
part because they are built for the target hardware.
The environment setup script is added so that you can initialize
the environment before using the tools.
Notes
The Yocto Project supports several methods by which you can set up this cross-development environment. These methods include downloading pre-built SDK installers or building and installing your own SDK installer.
For background information on cross-development toolchains in the Yocto Project development environment, see the "Cross-Development Toolchain Generation" section.
For information on setting up a cross-development environment, see the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual.
Once built, the SDK installers are written out to the
deploy/sdk folder inside the
Build Directory
as shown in the figure at the beginning of this section.
Depending on the type of SDK, several variables exist that help
configure these files.
The following list shows the variables associated with a standard
SDK:
DEPLOY_DIR: Points to thedeploydirectory.SDKMACHINE: Specifies the architecture of the machine on which the cross-development tools are run to create packages for the target hardware.SDKIMAGE_FEATURES: Lists the features to include in the "target" part of the SDK.TOOLCHAIN_HOST_TASK: Lists packages that make up the host part of the SDK (i.e. the part that runs on theSDKMACHINE). When you usebitbake -c populate_sdkto create the SDK, a set of default packages apply. This variable allows you to add more packages.imagenameTOOLCHAIN_TARGET_TASK: Lists packages that make up the target part of the SDK (i.e. the part built for the target hardware).SDKPATH: Defines the default SDK installation path offered by the installation script.
This next list, shows the variables associated with an extensible SDK:
DEPLOY_DIR: Points to thedeploydirectory.SDK_EXT_TYPE: Controls whether or not shared state artifacts are copied into the extensible SDK. By default, all required shared state artifacts are copied into the SDK.SDK_INCLUDE_PKGDATA: Specifies whether or not packagedata will be included in the extensible SDK for all recipes in the "world" target.SDK_INCLUDE_TOOLCHAIN: Specifies whether or not the toolchain will be included when building the extensible SDK.SDK_LOCAL_CONF_WHITELIST: A list of variables allowed through from the build system configuration into the extensible SDK configuration.SDK_LOCAL_CONF_BLACKLIST: A list of variables not allowed through from the build system configuration into the extensible SDK configuration.SDK_INHERIT_BLACKLIST: A list of classes to remove from theINHERITvalue globally within the extensible SDK configuration.