As we saw, Poky metadata starts with the meta, meta-poky, and meta-yocto-bsp layers, and it can be expanded by using more layers.
An index of the available OpenEmbedded layers that are compatible with the Yocto Project is maintained at http://layers.openembedded.org/.
An embedded product's development usually starts with hardware evaluation using a manufacturer's reference board design. Unless you are working with one of the reference boards already supported by Poky, you will need to extend Poky to support your hardware by adding extra BSP layers.
The first thing to do is to select which base hardware your design is going to be based on. We will use a board that is based on a NXP i.MX6 System on Chip (SoC) as a starting point for our embedded product design.
This recipe gives an overview of the support for NXP hardware in the Yocto Project.
The SoC manufacturer (in this case, NXP) has a range of reference design boards for purchase, as well as official Yocto-based software releases. Similarly, other manufacturers that use NXP's SoCs offer reference design boards and their own Yocto-based BSP layers and even distributions.
Selecting the appropriate hardware to base your design on is one of the most important design decisions for an embedded product. Depending on your product needs, you will decide to either:
Most of the time, a production-ready board will not match the specific requirements of a professional embedded system, and the process of designing a complete carrier board using NXP's SoC would be too time consuming. So, using an appropriate module that already solves the most technically challenging design aspects is a common choice.
Some of the characteristics that are important to consider are:
- Industrial temperature ranges
- Power management
- Long-term availability
- Pre-certified wireless and Bluetooth (if applicable)
The Yocto community that support NXP-based boards is called the FSL community BSP and their main layers are called meta-freescale and meta-freescale-3rdparty. The Freescale brand was acquired by NXP with the purchase of Freescale. The selection of boards that are supported on meta-freescale is limited to NXP reference designs, which would be the starting point if you are considering designing your own carrier board around NXP's SoC. Boards from other vendors are maintained on the meta-freescale-3rdparty layer.
There are other embedded manufacturers that use meta-freescale, but they have not integrated their boards in the meta-freescale-3rdparty community layer. These manufacturers keep their own BSP layers, which depend on meta-freescale, with specific support for their hardware. An example of this is Digi International and its ConnectCore product range, with the Yocto layers available at https://github.com/digi-embedded/meta-digi. There is also a Yocto-based distribution available called Digi Embedded Yocto.
To understand NXP's Yocto ecosystem, we need to start with the FSL community BSP, comprising the meta-freescale layer with support for NXP's reference boards, and its companion, meta-freescale-3rdparty, with support for boards from other vendors, and its differences with the official NXP Yocto BSP releases that NXP offers for their reference designs.
There are some key differences between the community and NXP Yocto releases:
- NXP releases are developed internally by NXP without community involvement and are used for BSP validation on NXP reference boards.
- NXP releases go through an internal QA and validation test process, and they are maintained by NXP support.
- NXP releases for a specific platform reach a maturity point, after which they are no longer worked on. At this point, all the development work has been integrated into the community layer and the platforms are further maintained by the FSL BSP community.
- NXP Yocto releases are not Yocto compatible, while the community release is.
NXP's engineering works very closely with the FSL BSP community to make sure that all development in their official releases is integrated in the community layer in a reliable and quick manner.
The FSL BSP community is also very responsive and active, so problems can usually be worked on with them to benefit all parts.
The FSL community BSP extends Poky with the following layers:
meta-freescale: This is the community layer that supports NXP reference designs. It has a dependency on OpenEmbedded-Core. Machines in this layer will be maintained even after NXP stops active development on them. You can downloadmeta-freescalefrom its Git repository at http://git.yoctoproject.org/cgit/cgit.cgi/meta-freescale/.
Development discussions can be followed and contributed to by visiting the development mailing list at https://lists.yoctoproject.org/listinfo/meta-freescale.
The meta-freescale layer provides both the i.MX6 Linux kernel and the U-Boot source either from NXP's or from FSL community BSP maintained repositories using the following links:
- NXP's Linux kernel Git repository: http://git.freescale.com/git/cgit.cgi/imx/linux-imx.git/
- FSL community Linux kernel Git repository: https://github.com/Freescale/linux-fslc.git
- NXP's U-Boot Git repository: http://git.freescale.com/git/cgit.cgi/imx/uboot-imx.git/
- FSL community U-Boot Git repository: https://github.com/Freescale/u-boot-fslc.git
Other Linux kernel and U-Boot versions are available, but keeping the manufacturer's supported version is recommended.
The meta-freescale layer includes NXP's proprietary binaries to enable some hardware features—most notably its hardware graphics, multimedia, and encryption capabilities. To make use of these capabilities, the end user needs to accept the NXP End-User License Agreement (EULA), which is included in the meta-freescale layer.
meta-freescale-3rdparty: This layer adds support for other community-maintained boards, for example, the Wandboard. To download the layer's content, you may visit https://github.com/Freescale/meta-freescale-3rdparty/.
meta-freescale-distro: This layer adds a metadata layer for demonstration target images. To download the layer's content, you may visit https://github.com/Freescale/meta-freescale-distro.
This layer adds two different sets of distributions, one maintained by the FSL BSP community (fslc- distributions) and one maintained by NXP (fsl- distributions). They are a superset of Poky that allows you to easily choose the graphical backend to use between:
- framebuffer
- x11
- Wayland
- XWayland
We will learn more about the different graphical backends in Chapter 4, Application Development.
NXP uses another layer on top of the layers previously mentioned for their official software releases:
meta-fsl-bsp-release: This is an NXP-maintained layer that is used in the official NXP software releases. It contains modifications to bothmeta-freescaleandmeta-freescale-distro. It is not part of the community release but can be accessed at http://git.freescale.com/git/cgit.cgi/imx/meta-fsl-bsp-release.git/.
NXP-based platforms extended layers hierarchy
For more information, refer to the FSL community BSP web page available at http://freescale.github.io/
NXP's official support community can be accessed at https://community.nxp.com/