RDK adopted Yocto build framework over legacy build systems after considering many of its advantages such as:

• Easy migration to different hardware platform
• Reduces the build time
• Supports major embedded architectures
• Provides a layered mechanism
• Easy to extend the configuration
• Reduce the cost of development
• RDK wanted to have a common infrastructure which supports multiple architectures
• Standard Distribution and tools
• Focus on specific product features and development.
• Its looking for a scalable system to meet the RDK community needs.
• Collaborate on open source infrastructure.

RDK Yocto Layer Structure

The below diagram shows the Yocto layer structure designed to build RDK stack. Layer definition is present in build/conf/bblayers.conf

MSO specific recipes and configuration to be placed in

• meta-rdk-<mso-name>

OEM specific recipes and configuration to be placed in

• meta-rdk-oem-<oem-name>

SoC specific recipes and configuration to be placed in

• meta-rdk-soc-<soc-name> 

BSP layer and associated recipes:

• meta-rdk-bsp-<soc-bsp-layer> - example: meta-rdk-broadcom
• meta-rdk-bsp--<oem-bsp-layer> - example: meta-rdk-pace
• meta-rdk-bsp-skeleton - This is a sample BSP layer implementation

1. recipes-bsp : Contains board specific recipes, for example OpenGL, Driver Specific on Board
2. recipes-kernel : Contains recipes for machine specific kernel and drivers
3. recipes-core : Contains recipes for modules like busybox, mtdtools, jpeg, etc.
4. recipes-devtools : Machine specific developments tools like bison etc.
5. recipes-extended : Machine specific RDK components, ex: iarmmgrs, mediaplayer, dshalapp etc.
6. recipes-multimedia : Machine specific multimedia components like gstplayer, framebufffer etc.
7. recipes-qt : Recipes related to SoC provided Qt and its components like Qt google browser, etc.
8. recipes-support : Board specific support components like remote control libs etc.

Generic Yocto layers

The generic yocto layers are needed along with the BSP layer for the build. They are:

• meta-openembedded
• meta-rdk
• meta-java
• meta-virtualization
• openembedded-core
• meta-linaro (for toolchain cross compilation – ARM only)
• meta-qt5 (generic qt layer)

RDK Meta-layers

meta-rdk:

• Distribution policies(modeled from Poky)
• Common RDK component recipes

meta-cmf:

• Common RDK component recipe append files & patches
• Overrides the meta-rdk recipes

meta-rdk-bsp-emulator:

• Boards support layer
• Contains qemux86hyb and qemux86mc machines
• Reference for porting
• Create meta-rdk-bsp delta layers for existing BSPs

meta-cmf-bsp-emulator:

• Contains RDK component recipe append files & patches, which are required for RDK PC emulator

SoC Layer

Contents of SoC layer shall be

• recipes (.bb) to build Kernel
• recipes(.bb)  to build SDK
• Kernel patches (SoC specific - if any)
• SDK patches (SoC specific - if any)
• Any SoC specific scripts or files which need to be installed in RFS

• Same SoC layer can be integrated with different OEM layers

OEM Layer

Contents of OEM layer shall be

• recipes(.bbappend) to build Kernel if there is any OEM specific configuration or patch is required. It shall be a .bbappend file of corresponding recipe file in SoC layer
• recipes(.bbappend) to build SDK if there is any OEM specific configuration or patch is required.. It shall be a .bbappend file of corresponding recipe file in SoC layer
• recipes(.bb) for packaging the images
• Kernel patches (OEM specific - if any)
• SDK patches (OEM specific - if any)
• Any OEM specific scripts or files which need to be installed in RFS
• Device(machine) configuration file(.conf)

Separate layers must be available for an OEM, if different SoCs are used
"meta-rdk-oem-OEM-X-SOC-Y","meta-rdk-oem-OEM-X-SOC-Z“, etc.

The SoC / OEM layer shall NOT contain

• Source code
• Binaries
• Tools
• Tar balls (of any of the above)

Bitbake work-flow

• All the components are built using individual recipes. There shall be a main image recipe (example , rdk-generic-image) which includes all other required recipe and create the final RFS
• Package groups recipe is one support a image recipe to select the set of packages
• The recipes will be called in sequence
  (1) opensource components
  (2) Kernel
  (3) SDK
  (4) RDK
  (5) MSO
  (6) Packaging and create final image.
• The final linux and RFS  image will be created under build_folder/tmp/deploy/images

RDK Package Groups

• packagegroup-rdk-baserootfs - contains common generic RDK OSS components.
• packagegroup-rdk-oss-mediaserver - contains OSS components specific to media server
• packagegroup-rdk-oss-mediaclient - contains OSS components specific to mediaclient
• packagegroup-rdk-media-common - contains common RDK (non-OSS) components for mediaclient, mediaserver build types.
• packagegroup-rdk-generic-mediaserver - contains mediaserver specific RDK components
• packagegroup-rdk-generic-mediaclient - contains mediaclient specific RDK components

RDK Yocto Images

Yocto build Image target names roughly look like  <RDK vendor>-<profile>-<build-type>-<developer>-image