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user: Add x86_64 BSP chapter
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Amaan Cheval
Joel Sherrill
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.. comment SPDX-License-Identifier: CC-BY-SA-4.0
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.. comment Copyright (c) 2018 Amaan Cheval <amaan.cheval@gmail.com>
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.. comment Copyright (c) 2018 embedded brains GmbH
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x86_64
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******
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There are no x86_64 BSPs yet.
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amd64
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=====
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This BSP offers only one variant, ``amd64``. The BSP can run on UEFI-capable
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systems by using FreeBSD's bootloader, which then loads the RTEMS executable (an
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ELF image).
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Currently only the console driver and context initialization and switching are
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functional (to a bare minimum), but this is enough to run the ``hello.exe`` sample
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in the RTEMS testsuite.
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Build Configuration Options
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---------------------------
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There are no options available to ``configure`` at build time, at the moment.
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Testing with QEMU
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-----------------
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To test with QEMU, we need to:
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- Build / install QEMU (most distributions should have it available on the
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package manager).
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- Build UEFI firmware that QEMU can use to simulate an x86-64 system capable of
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booting a UEFI-aware kernel, through the ``--bios`` flag.
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Building TianoCore's UEFI firmware, OVMF
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Complete detailed instructions are available at `TianoCore's Github's wiki
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<https://github.com/tianocore/tianocore.github.io/wiki/How-to-build-OVMF>`_.
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Quick instructions (which may fall out of date) are:
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.. code-block:: shell
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$ git clone git://github.com/tianocore/edk2.git
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$ cd edk2
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$ make -C BaseTools
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$ . edksetup.sh
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Then edit ``Conf/target.txt`` to set:
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::
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ACTIVE_PLATFORM = OvmfPkg/OvmfPkgX64.dsc
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TARGET = DEBUG
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TARGET_ARCH = X64
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# You can use GCC46 as well, if you'd prefer
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TOOL_CHAIN_TAG = GCC5
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Then run ``build`` in the ``edk2`` directory - the output should list the
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location of the ``OVMF.fd`` file, which can be used with QEMU to boot into a UEFI
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shell.
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You can find the ``OVMF.fd`` file like this as well in the edk2 directory:
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.. code-block:: shell
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$ find . -name "*.fd"
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./Build/OvmfX64/DEBUG_GCC5/FV/MEMFD.fd
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./Build/OvmfX64/DEBUG_GCC5/FV/OVMF.fd <-- the file we're looking for
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./Build/OvmfX64/DEBUG_GCC5/FV/OVMF_CODE.fd
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./Build/OvmfX64/DEBUG_GCC5/FV/OVMF_VARS.fd
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Boot RTEMS via FreeBSD's bootloader
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-----------------------------------
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The RTEMS executable produced (an ELF file) needs to be placed in the FreeBSD's
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``/boot/kernel/kernel``'s place.
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To do that, we first need a hard-disk image with FreeBSD installed on
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it. `Download FreeBSD's installer "memstick" image for amd64
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<https://www.freebsd.org/where.html>`_ and then run the following commands,
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replacing paths as appropriate.
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.. code-block:: shell
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$ qemu-img create freebsd.img 8G
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$ OVMF_LOCATION=/path/to/ovmf/OVMF.fd
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$ FREEBSD_MEMSTICK=/path/to/FreeBSD-11.2-amd64-memstick.img
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$ qemu-system-x86_64 -m 1024 -serial stdio --bios $OVMF_LOCATION \
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-drive format=raw,file=freebsd.img \
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-drive format=raw,file=$FREEBSD_MEMSTICK
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The first time you do this, continue through and install FreeBSD. `FreeBSD's
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installation guide may prove useful
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<https://www.freebsd.org/doc/handbook/bsdinstall-start.html>`_ if required.
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Once installed, build your RTEMS executable (an ELF file), for
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eg. ``hello.exe``. We need to transfer this executable into ``freebsd.img``'s
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filesystem, at either ``/boot/kernel/kernel`` or ``/boot/kernel.old/kernel`` (or
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elsewhere, if you don't mind user FreeBSD's ``loader``'s prompt to boot your
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custom kernel).
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If your host system supports mounting UFS filesystems as read-write
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(eg. FreeBSD), go ahead and:
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1. Mount ``freebsd.img`` as read-write
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2. Within the filesystem, back the existing FreeBSD kernel up (i.e. effectively
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``cp -r /boot/kernel /boot/kernel.old``).
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3. Place your RTEMS executable at ``/boot/kernel/kernel``
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If your host doesn't support mounting UFS filesystems (eg. most Linux kernels),
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do something to the effect of the following.
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On the host
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.. code-block:: shell
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# Upload hello.exe anywhere accessible within the host
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$ curl --upload-file hello.exe https://transfer.sh/rtems
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Then on the guest (FreeBSD), login with ``root`` and
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.. code-block:: shell
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# Back the FreeBSD kernel up
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$ cp -r /boot/kernel/ /boot/kernel.old
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# Bring networking online if it isn't already
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$ dhclient em0
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# You may need to add the --no-verify-peer depending on your server
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$ fetch https://host.com/path/to/rtems/hello.exe
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# Replace default kernel
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$ cp hello.exe /boot/kernel/kernel
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$ reboot
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After rebooting, the RTEMS kernel should run after the UEFI firmware and
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FreeBSD's bootloader. The ``-serial stdio`` QEMU flag will let the RTEMS console
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send its output to the host's ``stdio`` stream.
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Clock Driver
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------------
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The clock driver currently uses the idle thread clock driver.
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Console Driver
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--------------
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The console driver defaults to using the ``COM1`` UART port (at I/O port
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``0x3F8``), using the ``NS16550`` polled driver.
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