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This guide is intended to help developers understand the Yocto framework in RDK so they can extend the existing functionality. 

BitBake Main Tasks

Bitbake executes all the layers starting with a prefix ‘meta’. It parses the build classes, configuration files, and recipes and executes each task by creating a shell script on-the-fly.

TASK

DESCRIPTION

FUNCTION

Build

Default task for a recipe - depends on all other normal tasks required to 'build' a recipe

do_build

Init RAMFS

Combines an initial ramdisk image and kernel together to form a single image

do_bundle_initramfs

Check URI

Validates the SRC_URI value

do_checkuri

Clean

Removes all output files for a target

do_clean

Clean all

Removes all output files, shared state cache, and downloaded source files for a target

do_cleanall

Clean SSTATE

Removes all output files and shared state cache for a target

do_cleansstate

Compile

Compiles the source in the compilation directory

do_compile

Configure

Configures the source by enabling and disabling any build-time and configuration options for the software being built

do_configure

Dev Shell

Starts a shell with the environment set up for development/debugging

do_devshell

Fetch

Fetches the source code

do_fetch

Install

Copies files from the compilation directory to a holding area

do_install

List Tasks

Lists all defined tasks for a target

do_listtasks

Package

Analyzes the content of the holding area and splits it into subsets based on available packages and files

do_package

Package QA

Runs QA checks on packaged files

do_package_qa

Write IPK

Creates the actual IPK packages and places them in the Package Feed area

do_package_write_ipk

Patch

Locates patch files and applies them to the source code

do_patch

Populate License

Writes license information for the recipe that is collected later when the image is constructed

do_populate_lic

Populate SDK

Creates the file and directory structure for an installable SDK

do_populate_sdk

Populate SYSROOT

Copies a subset of files installed by do_install into the sysroot in order to make them available to other recipes

do_populate_sysroot

Root FS

Creates the root filesystem (file and directory structure) for an image

do_rootfs

Unpack

Unpacks the source code into a working directory

do_unpack


Configuration

Configuration (*.conf) comprises of global definition of variables. There are two types of configurations:

  • User configuration
  • Machine configuration(BSP)

User Configuration

build directory

Machine/BSP Configuration

BSPs are layers that add machine settings and recipes. It contains extensions and customizations to base system. They are added to the BBLAYERS variable in build/conf/bblayers.conf
Machine settings are specified in a layer's conf/machine/xxx.conffile(s)
For Example:

../meta-rdk-bsp-emulator/conf/machine/qemux86hyb.conf

For Device:

../meta-rdk-oem-<OEM Name>-<SoCName>/conf/machine/<configuration_file_name>.conf

RDK Recipes

Recipes are the most basic metadata files which are denoted by the file extension*.bb. Recipes can build one or more packages from source code.

They provide:

  • Descriptive information about the package
  • Existing dependencies (both build and runtime dependencies)
  • DEPENDS & RDEPENDS variables holds the build & runtime dependencies e.g.
  • DEPENDS = "closedcaption-hal-headers"
  • RDEPENDS = "libcrypto"
  • Where the source code resides and how to fetch it,
  • SRC_URI variable holds the URL path to fetch
  • SRC_URI = "${RDK_GENERIC_ROOT_GIT}/devicesettings/generic;protocol=${RDK_GIT_PROTOCOL};branch=${RDK_GIT_BRANCH}"
  • The version of the recipe
  • SRCREV= "${AUTOREV}" /
  • SRCREV= "6c492f7452a6b4b240f1b572dbda2f2bcc4faf2d"
  • Whether the source code requires any patches, where to find them, and how to apply them
  • How to configure and compile the source code
  • Where on the target machine to install the package or packages created

Recipe Append files

Append files are identified by the extension *.bbappend. They are used to extend or override information in an existing recipe file. BitBake expects every append file to have a corresponding recipe (*.bb) file. A missing .bb file will be shown as an warning by the BitBake parser. The append file and corresponding recipe file must use the same root filename.
Example:  devicesettings_git.bb & devicesettings_git.bbappend

Bitbake variables/meta data

These are set automatically by bitbake. 

  • TOPDIR – The build directory
  • LAYERDIR – Current layer directory
  • FILE – Path and filename of file being processed

Build time meta-data

  • PN – Pakage name (“myrecipe”)
  • PV – Package version (1.0)
  • PR – Package Release (r0)
  • P = “${PN}-${PV}”
  • PF = “${PN}-${PV}-${PR}”
  • FILE_DIRNAME – Directory for FILE
  • FILESPATH = "${FILE_DIRNAME}/${PF}:\
  • TOPDIR – The build directory
  • TMPDIR = “${TOPDIR}/tmp”
  • WORKDIR = ${TMPDIR}/work/${PF}”
  • S = “${WORKDIR}/${P}” (Source dir)
  • B = “${S}” (Build dir)
  • D = “${WORKDIR}/${image}” (Destination dir)
  • DEPLOY_DIR = “${TMPDIR}/deploy”
  • DEPLOY_DIR_IMAGE = “${DEPLOY_DIR}/images”

Dependency meta-data

Build time package variables

  • DEPENDS – Build time package dependencies
  • PROVIDES = “${P} ${PF} ${PN}”

Runtime package variables

  • RDEPENDS – Runtime package dependencies
  • RRECOMMENDS – Runtime recommended packages
  • RSUGGESTS – Runtime suggested packages
  • RPROVIDES – Runtime provides
  • RCONFLICTS – Runtime package conflicts
  • RREPLACES – Runtime package replaces

Common meta-data

Variables you commonly set

  • SUMMARY – Short description of package/recipe
  • HOMEPAGE – Upstream web page
  • LICENSE – Licenses of included source code
  • LIC_FILES_CHKSUM – Checksums of license files at time of packaging (checked for change by build)
  • SRC_URI – URI of source code, patches and extra files to be used to build packages. Uses different fetchers based on the URI.
  • FILES – Files to be included in binary packages

Patching

Patches can be applied to recipe files. Patch files extension *.patch. Place the patch file in subdirectory of recipe named (component) folder. The subdirectory should be preferably named as that of component or as ‘files’. Add the below line to the recipe file
SRC_URI += "file://temp.patch"

More information on patches can be found here

Prebuilts with Yocto

SSTATE ( shared state ) is the way OE speeds up builds. A much detailed conceptual description please read http://www.yoctoproject.org/docs/current/ref-manual/ref-manual.html#shared-state-cache 

OE/Yocto has a feature called SSTATE(shared state) to deliver prebuilts amongst users. Shared state is currently configured with OE/Yocto projects.




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