ACRN UOS (User Operating System)


This board configuration defines an ACRN User OS execution environment for running Zephyr RTOS applications.

ACRN is a flexible, lightweight reference hypervisor, built with real-time and safety-criticality in mind, optimized to streamline embedded development through an open source platform. Check out the Introduction to Project ACRN for more information.

This baseline configuration can be used as a starting point for creating demonstration ACRN UOS configurations. It currently supports the following devices:

  • I/O APIC

  • local APIC timer

  • NS16550 UARTs


This ACRN board configuration is for illustrative purposes only. Because of its reliance on virtualized hardware provided by ACRN, it is not suitable for production real-time applications. Real-time response under ACRN requires direct access to the underlying hardware, so production applications should be derived from the board configurations that describe that underlying hardware.

For example, if you wish to run an application under ACRN on an Up Squared, start with the Up Squared board configuration, not this one.

Serial Ports

The serial ports are assumed present at traditional COM1: and COM2: I/O-space addresses (based at 0x3f8 and 0x2f8, respectively). Only polled operation is supported in this baseline configuration, as IRQ assignments under ACRN are configurable (and frequently non-standard). Interrupt-driven and MMIO operation are also possible.

Building and Running

This details the process for building the Hello World sample and running it as an ACRN User OS.

On the Zephyr Build System

  1. The build process for the ACRN UOS target is similar to other boards. We will build the Hello World sample for ACRN with:

    # From the root of the zephyr repository
    west build -b acrn samples/hello_world

    This will build the application ELF binary in samples/hello_world/build/zephyr/zephyr.elf.

  2. Build GRUB2 boot loader image

    We can build the GRUB2 bootloader for Zephyr using boards/x86/common/scripts/

    $ ./boards/x86/common/scripts/ x86_64

    The EFI executable will be found at boards/x86/common/scripts/grub/bin/grub_x86_64.efi.

  3. Preparing the boot device

    $ dd if=/dev/zero of=zephyr.img bs=1M count=35
    $ mkfs.vfat -F 32 zephyr.img
    $ LOOP_DEV=`sudo losetup -f -P --show zephyr.img`
    $ sudo mount $LOOP_DEV /mnt
    $ sudo mkdir -p /mnt/efi/boot
    $ sudo cp boards/x86/common/scripts/grub/bin/grub_x86_64.efi /mnt/efi/boot/bootx64.efi
    $ sudo mkdir -p /mnt/kernel
    $ sudo cp samples/hello_world/build/zephyr/zephyr.elf /mnt/kernel

    Create /mnt/efi/boot/grub.cfg containing the following:

    set default=0
    set timeout=10
    menuentry "Zephyr Kernel" {
        multiboot /kernel/zephyr.elf

    And then unmount the image file:

    $ sudo umount /mnt

    You now have a virtual disk image with a bootable Zephyr in zephyr.img. If the Zephyr build system is not the ACRN SOS, then you will need to transfer this image to the ACRN SOS (via, e.g., a USB stick or network).


  1. If you are not already using the ACRN SOS, follow Getting Started Guide for ACRN Industry Scenario With Ubuntu Service VM to install and boot “The ACRN Service OS”.

  2. Boot Zephyr as User OS

    On the ACRN SOS, prepare a directory and populate it with Zephyr files.

    $ mkdir zephyr
    $ cd zephyr
    $ cp /usr/share/acrn/samples/nuc/ .
    $ cp /usr/share/acrn/bios/OVMF.fd .

    You will also need to copy the zephyr.img created in the first section into this directory. Then run script to launch the Zephyr as a UOS.

    $ sudo ./

    Then Zephyr will boot up automatically. You will see the banner:

    Hello World! acrn

    Which indicates that Zephyr is running successfully under ACRN!