.. comment SPDX-License-Identifier: CC-BY-SA-4.0
.. comment Copyright (c) 2018 Amaan Cheval <amaan.cheval@gmail.com>
.. comment Copyright (c) 2018 embedded brains GmbH

x86_64
******

amd64
=====

This BSP offers only one variant, ``amd64``. The BSP can run on UEFI-capable
systems by using FreeBSD's bootloader, which then loads the RTEMS executable (an
ELF image).

Currently only the console driver and context initialization and switching are
functional (to a bare minimum), but this is enough to run the ``hello.exe`` sample
in the RTEMS testsuite.

Build Configuration Options
---------------------------

There are no options available to ``configure`` at build time, at the moment.

Testing with QEMU
-----------------

To test with QEMU, we need to:

- Build / install QEMU (most distributions should have it available on the
  package manager).
- Build UEFI firmware that QEMU can use to simulate an x86-64 system capable of
  booting a UEFI-aware kernel, through the ``--bios`` flag.

Building TianoCore's UEFI firmware, OVMF
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Complete detailed instructions are available at `TianoCore's Github's wiki
<https://github.com/tianocore/tianocore.github.io/wiki/How-to-build-OVMF>`_.

Quick instructions (which may fall out of date) are:

.. code-block:: shell

    $ git clone git://github.com/tianocore/edk2.git
    $ cd edk2
    $ make -C BaseTools
    $ . edksetup.sh

Then edit ``Conf/target.txt`` to set:

::

    ACTIVE_PLATFORM       = OvmfPkg/OvmfPkgX64.dsc
    TARGET                = DEBUG
    TARGET_ARCH           = X64
    # You can use GCC46 as well, if you'd prefer
    TOOL_CHAIN_TAG        = GCC5

Then run ``build`` in the ``edk2`` directory - the output should list the
location of the ``OVMF.fd`` file, which can be used with QEMU to boot into a UEFI
shell.

You can find the ``OVMF.fd`` file like this as well in the edk2 directory:

.. code-block:: shell

    $ find . -name "*.fd"
    ./Build/OvmfX64/DEBUG_GCC5/FV/MEMFD.fd
    ./Build/OvmfX64/DEBUG_GCC5/FV/OVMF.fd <-- the file we're looking for
    ./Build/OvmfX64/DEBUG_GCC5/FV/OVMF_CODE.fd
    ./Build/OvmfX64/DEBUG_GCC5/FV/OVMF_VARS.fd

Boot RTEMS via FreeBSD's bootloader
-----------------------------------

The RTEMS executable produced (an ELF file) needs to be placed in the FreeBSD's
``/boot/kernel/kernel``'s place.

To do that, we first need a hard-disk image with FreeBSD installed on
it. `Download FreeBSD's installer "memstick" image for amd64
<https://www.freebsd.org/where.html>`_ and then run the following commands,
replacing paths as appropriate.

.. code-block:: shell

   $ qemu-img create freebsd.img 8G
   $ OVMF_LOCATION=/path/to/ovmf/OVMF.fd
   $ FREEBSD_MEMSTICK=/path/to/FreeBSD-11.2-amd64-memstick.img
   $ qemu-system-x86_64 -m 1024 -serial stdio --bios $OVMF_LOCATION \
       -drive format=raw,file=freebsd.img \
       -drive format=raw,file=$FREEBSD_MEMSTICK

The first time you do this, continue through and install FreeBSD. `FreeBSD's
installation guide may prove useful
<https://www.freebsd.org/doc/handbook/bsdinstall-start.html>`_ if required.

Once installed, build your RTEMS executable (an ELF file), for
eg. ``hello.exe``. We need to transfer this executable into ``freebsd.img``'s
filesystem, at either ``/boot/kernel/kernel`` or ``/boot/kernel.old/kernel`` (or
elsewhere, if you don't mind user FreeBSD's ``loader``'s prompt to boot your
custom kernel).

If your host system supports mounting UFS filesystems as read-write
(eg. FreeBSD), go ahead and:

1. Mount ``freebsd.img`` as read-write
2. Within the filesystem, back the existing FreeBSD kernel up (i.e. effectively
   ``cp -r /boot/kernel /boot/kernel.old``).
3. Place your RTEMS executable at ``/boot/kernel/kernel``

If your host doesn't support mounting UFS filesystems (eg. most Linux kernels),
do something to the effect of the following.

On the host

.. code-block:: shell

   # Upload hello.exe anywhere accessible within the host
   $ curl --upload-file hello.exe https://transfer.sh/rtems

Then on the guest (FreeBSD), login with ``root`` and

.. code-block:: shell

   # Back the FreeBSD kernel up
   $ cp -r /boot/kernel/ /boot/kernel.old
   # Bring networking online if it isn't already
   $ dhclient em0
   # You may need to add the --no-verify-peer depending on your server
   $ fetch https://host.com/path/to/rtems/hello.exe
   # Replace default kernel
   $ cp hello.exe /boot/kernel/kernel
   $ reboot

After rebooting, the RTEMS kernel should run after the UEFI firmware and
FreeBSD's bootloader. The ``-serial stdio`` QEMU flag will let the RTEMS console
send its output to the host's ``stdio`` stream.

Clock Driver
------------

The clock driver currently uses the idle thread clock driver.

Console Driver
--------------

The console driver defaults to using the ``COM1`` UART port (at I/O port
``0x3F8``), using the ``NS16550`` polled driver.