Armv8-R AArch64 Extras Layer (meta-armv8r64-extras)

Zephyr Sample Applications

This Software Stack supports four Zephyr sample applications:

  • zephyr-helloworld

  • zephyr-synchronization

  • zephyr-philosophers

  • zephyr-rpmsg-demo (Zephyr part of RPMsg Demo)

Recipes for zephyr-helloworld, zephyr-synchronization and zephyr-philosophers are provided by meta-zephyr. Source code for these three sample applications are provided by Zephyr, with extra configuration provided for zephyr-philosophers by file meta-armv8r64-extras/dynamic-layers/zephyrcore/recipes-kernel/zephyr-kernel/zephyr-philosophers.bbappend. These three applications can work in both the baremetal stack and the Virtualization stack.

The zephyr-rpmsg-demo application works in the Virtualization stack only. It comes from the recipe meta-armv8r64-extras/dynamic-layers/virtualization-layer/recipes-kernel/zephyr-kernel/ This application works as a RPMsg host (rpmsg-host) in the Zephyr domain, and co-works with the RPMsg remote application (rpmsg-remote) running in the Linux domain to implement the Inter-VM communication through the RPMsg protocol. Recipe for the rpmsg-remote application is provided by meta-armv8r64-extras/dynamic-layers/virtualization-layer/recipes-demo/rpmsg-demo/, which along with is provided by this Software Stack. The source code is also provided by this Software Stack and can be found in directory components/apps/rpmsg-demo. For more details, see RPMsg Demo under Demo Applications.

Running Zephyr applications is supported by the runfvp script from meta-arm. Section Build and Run has examples that uses this script.

Virtualization Stack

The Virtualization stack uses Xen as the Type-1 hypervisor to boot one or more domains independently. The meta-virtualization layer is used to provide Xen build support.

The Xen MPU implementation only supports “dom0less” mode (for more details see the Hypervisor (Xen) section), so the meta-armv8r64-extras layer provides logic to build the required dom0less artifacts, which are shown in the diagram below. For more information on how U-Boot detects and uses these artifacts at runtime, see the U-Boot Boot Sequence.

Arm v8r64 Xen stack

Domain Configuration

The default domain configuration is provided in a bbclass. For more information, see Customizing the Xen Domains.

Xen Configuration

Xen is configured through the .bb and .bbappend files in directory meta-armv8r64-extras/dynamic-layers/virtualization-layer/recipes-extended/xen, which define the branch and revision to build for the fvp-baser-aemv8r64 machine and also includes a machine-specific config file.

Linux Image Configuration

In projects based on OE-core, the Linux image recipe is responsible for creating the disk image, including the root filesystem partition. The boot partition, which is part of the same disk image, is populated by extending IMAGE_CLASSES (see Image Generation below).

No changes are made to the Linux kernel for the Virtualization use case.

Zephyr Application Configuration

Zephyr requires some specific configuration when running as a Xen domain on the fvp-baser-aemv8r64 machine. It is necessary to match the number of CPUs allocated, the DRAM address and the selected UART with the equivalent parameters in the domain configuration. This is achieved using Xen-specific overlay files (see Customizing the Zephyr Configuration).

Device Tree Generation

Xen domains in dom0less mode are configured using additions to the /chosen node in the device tree. To avoid modifying the firmware’s device tree for the Virtualization stack we instead dynamically generate a device tree overlay file which can be applied at runtime by U-Boot. Additionally, in order for Xen to access peripherals in dom0less mode, we must specify which peripherals to “pass through” to each domain using a domain-specific passthrough dtb file (see for more details).

All these device trees are created from templates, substituting placeholders with values defined in the domain configuration. The passthrough device tree template to use for each domain is selected in the domain configuration.

U-Boot Script Generation

The boot script is partially dynamically generated in order to load the configured domain binaries and passthrough device trees to the configured memory addresses prior to booting Xen.

Image Generation

The boot partition needs to be populated with the artifacts necessary to boot Xen and its domains so they can be loaded by U-Boot. This is achieved using a custom Wic image and a custom bbclass (xen_image_dom0less). This class can be added to IMAGE_CLASSES so that the desired Linux image recipe (e.g. core-image-minimal) includes the necessary configuration to populate the boot partition.