178 lines
5.2 KiB
ReStructuredText
178 lines
5.2 KiB
ReStructuredText
.. xenvm:
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ARMv8 Xen Virtual Machine Example
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#################################
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Overview
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********
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This board allows to run Zephyr as Xen guest on any ARMv8 board that supports
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ARM Virtualization Extensions. This is example configuration, as almost any VM
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configuration is unique in many aspects.
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.. figure:: xen_project_logo.png
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:align: center
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:alt: XenVM
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Xen virtual Guest (Credit: Xen Project)
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It provides minimal set of devices:
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* ARM Generic timer
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* GICv2
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Hardware
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********
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Supported Features
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==================
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The following hardware features are supported:
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+--------------+-------------+----------------------+
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| Interface | Controller | Driver/Component |
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+==============+=============+======================+
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| GIC | virtualized | interrupt controller |
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+--------------+-------------+----------------------+
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| ARM TIMER | virtualized | system clock |
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+--------------+-------------+----------------------+
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The kernel currently does not support other hardware features on this platform.
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Devices
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========
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System Clock
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------------
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This board configuration uses a system clock frequency of 8.32 MHz. This is the
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default value, which should be corrected for user's actual hardware.
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You can determine clock frequency of your ARM Generic Timer by inspecting Xen
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boot log:
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::
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(XEN) [ 0.147541] Generic Timer IRQ: phys=30 hyp=26 virt=27 Freq: 8320 KHz
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Interrupt Controller
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--------------------
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By default, GICv2 is selected. If your hardware is based on GICv3, you can
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configure Zephyr to use it, by amending device tree and Kconfig
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option in "xenvm" SoC as well as guest configuration file.
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CPU Core type
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-------------
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Default core in this configuration is Cortex A72. Depending on yours actual
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hardware you might want to change this option in the same way as Interrupt
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Controller configuration.
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Known Problems or Limitations
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==============================
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Xen configures guests in runtime by providing device tree that describes guest
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environment. On other hand, Zephyr uses static configuration that should be know
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at build time. So there are chances, that Zephyr image created with default
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configuration would not boot on your hardware. In this case you need to update
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configuration by altering device tree and Kconfig options. This will be covered
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in detail in next section.
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Most of Xen-specific features are not supported at the moment. This includes:
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* Xen Enlighten memory page (under development)
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* XenBus
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* Xen event channels (under development)
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* Xen grant tables
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* Xen PV drivers
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Now only following features are supported:
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* Xen PV console (UART-like driver with poll API, IRQ driven is under development)
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* Xen early console_io interface (mainly for debug purposes)
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Building and Running
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********************
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Use this configuration to run basic Zephyr applications and kernel tests as Xen
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guest, for example, with the :ref:`synchronization_sample`:
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.. code-block::
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$ west build -b xenvm samples/synchronization
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This will build an image with the synchronization sample app. Next, you need to
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create guest configuration file :code:`zephyr.conf`. There is example:
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.. code-block::
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kernel="zephyr.bin"
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name="zephyr"
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vcpus=1
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memory=16
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gic_version="v2"
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on_crash="preserve"
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You need to upload both :code:`zephyr.bin` and :code:`zephyr.conf` to your Dom0
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and then you can run Zephyr by issuing
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.. code-block::
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$ xl create zephyr.conf
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Next you need to attach to PV console:
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.. code-block::
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$ xl console zephyr
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Also this can be performed via single command:
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.. code-block::
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$ xl create -c zephyr.conf
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You will see Zephyr output:
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.. code-block:: console
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*** Booting Zephyr OS build zephyr-v2.4.0-1137-g5803ee1e8183 ***
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thread_a: Hello World from cpu 0 on xenvm!
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thread_b: Hello World from cpu 0 on xenvm!
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thread_a: Hello World from cpu 0 on xenvm!
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thread_b: Hello World from cpu 0 on xenvm!
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thread_a: Hello World from cpu 0 on xenvm!
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Exit xen virtual console by pressing :kbd:`CTRL+]`
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Updating configuration
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**********************
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As was said earlier, Xen describes hardware using device tree and expects that
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guest will parse device tree in runtime. On other hand, Zephyr supports only
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static, build time configuration. While provided configuration should work on
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almost any ARMv8 host running in aarch64 mode, there is no guarantee, that Xen
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will not change some values (like RAM base address) in the future.
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Also, frequency of system timer is board specific and should be updated when running
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Zephyr xenvm image on new hardware.
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One can make Xen to dump generated DTB by using :code:`LIBXL_DEBUG_DUMP_DTB`
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environment variable, like so:
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.. code-block::
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$ LIBXL_DEBUG_DUMP_DTB=domu-libxl.dtb xl create zephyr.conf
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Then, generated "domu-libxl.dtb" file can be de-compiled using "dtc" tool.
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Use information from de-compiled DTB file to update all related entries in
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provided "xenvm.dts" file. If memory layout is also changed, you may need to
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update :code:`CONFIG_SRAM_BASE_ADDRESS` as well.
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References
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**********
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`Xen ARM with Virtualization Extensions <https://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions>`_
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`xl.conf (guest configuration file) manual <https://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html>`_
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