..
 # Copyright (c) 2021-2022, Arm Limited.
 #
 # SPDX-License-Identifier: MIT

############
Yocto Layers
############

The ``meta-ewaol`` repository provides three layers compatible with the Yocto
Project, in the following sub-directories:

  * ``meta-ewaol-distro``

    Yocto distribution layer providing top-level and general policies for the
    EWAOL distribution images.

  * ``meta-ewaol-tests``

    Yocto software layer with recipes that include run-time tests to validate
    EWAOL functionalities.

  * ``meta-ewaol-bsp``

    Yocto BSP layer with target platform specific extensions for particular
    EWAOL distribution images.

    * For the N1SDP hardware target platform, this layer currently extends the
      ``n1sdp`` machine definition from the ``meta-arm-bsp`` layer for EWAOL
      virtualization distribution images.. The ``meta-ewaol-bsp`` layer contains
      an additional grub configuration file with Xen boot entry and a custom
      kickstart ``ewaol-virtualization-n1sdp-efidisk.wks.in`` file. There is
      also a ``xen-devicetree.bb`` recipe, to generate a devicetree with extra
      modules nodes required by Xen to start the Control VM (Dom0). In addition,
      the Xen devicetree together with a Xen efi binary are included into the
      final wic image in the ``boot`` partition.

    * For the AVA hardware target platform, this layer provides additional
      ``systemd`` configuration for ethernet interfaces based on the ``i40e`` as
      used on the AVA Developer Platform.

.. _manual_yocto_layers_layer_dependency_overview:

*************************
Layer Dependency Overview
*************************

The following diagram illustrates the layers which are integrated by the EWAOL
project, which are further expanded on below. |layer dependency statement|

|

.. image:: ../images/ewaol_layers_deps_diagram.png
   :align: center

|

EWAOL depends on the following layer dependency sources:

  .. code-block:: yaml
    :substitutions:

    URL: https://git.yoctoproject.org/git/poky
    layers: meta, meta-poky
    branch: |poky branch|
    revision: |poky revision|

    URL: https://git.openembedded.org/meta-openembedded
    layers: meta-filesystems, meta-networking, meta-oe, meta-python
    branch: |meta-openembedded branch|
    revision: |meta-openembedded revision|

    URL: https://git.yoctoproject.org/git/meta-virtualization
    layers: meta-virtualization
    branch: |meta-virtualization branch|
    revision: |meta-virtualization revision|

    URL: https://gitlab.arm.com/cassini/meta-cassini
    layer: meta-cassini-distro
    branch: |meta-cassini branch|
    revision: |meta-cassini revision|

Additional layer dependency sources may be conditionally required, depending on
the specific EWAOL distribution image being built.

The first additional layer dependency source is the ``meta-arm`` repository,
which provides three Yocto layers:

  .. code-block:: yaml
    :substitutions:

    URL: https://git.yoctoproject.org/git/meta-arm
    layers: meta-arm, meta-arm-bsp, meta-arm-toolchain
    branch: |meta-arm branch|
    revision: |meta-arm revision|

The layers required from ``meta-arm`` depend on the EWAOL distribution image:

  * EWAOL SDK distribution images require ``meta-arm`` and
    ``meta-arm-toolchain``, as the ``gator-daemon`` package is installed on the
    rootfs.

  * An EWAOL virtualization distribution image requires ``meta-arm`` and
    ``meta-arm-toolchain``, as by default a bundled Guest VM image based on the
    ``generic-arm64`` ``MACHINE`` is built.

  * An EWAOL distribution image built for the N1SDP hardware target platform
    requires ``meta-arm``, ``meta-arm-bsp``, and ``meta-arm-toolchain``.

These layers are described as follows:

  * ``meta-arm``:

    * URL: https://git.yoctoproject.org/cgit/cgit.cgi/meta-arm/tree/meta-arm.
    * Clean separation between Firmware and OS.
    * The canonical source for SystemReady firmware.

  * ``meta-arm-bsp``:

    * URL: https://git.yoctoproject.org/cgit/cgit.cgi/meta-arm/tree/meta-arm-bsp.
    * Board specific components for Arm target platforms.

  * ``meta-arm-toolchain``:

    * URL: https://git.yoctoproject.org/meta-arm/tree/meta-arm-toolchain.
    * Provides toolchain for Arm target platforms

The second additional layer dependency source is the ``meta-adlink-ampere``
repository, which provides a single Yocto layer:

  .. code-block:: yaml
    :substitutions:

    URL: https://github.com/ADLINK/meta-adlink-ampere.git
    layers: meta-adlink-ampere
    branch: |meta-adlink-ampere branch|
    revision: |meta-adlink-ampere revision|

This Yocto layer provides BSP components required when building an EWAOL
distribution image for the AVA hardware target platform.