93c3d32970
This adds support for booting entirely from JTAG while using a
hard-coded RCW. With these steps, it is not necessary to program a
"good" RCW using CodeWarrior. The method here can be performed with any
JTAG adapter supported by OpenOCD, including the on-board CMSIS-DAP
(albeit very slowly).
These steps require LS1046A support in OpenOCD, which was added in [1].
[1] 5b70c1f679/
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
[trini: Add reference to doc/board/nxp/ls1046ardb.rst]
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.. SPDX-License-Identifier: GPL-2.0+
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.. Copyright 2014 Broadcom Corporation.
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Semihosting
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===========
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Semihosting is ARM's way of having a real or virtual target communicate
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with a host or host debugger for basic operations such as file I/O,
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console I/O, etc. Please see `Arm's semihosting documentation
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<https://developer.arm.com/documentation/100863/latest/>`_ for more
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information.
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Platform Support
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----------------
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Versatile Express
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^^^^^^^^^^^^^^^^^
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For developing on armv8 virtual fastmodel platforms, semihosting is a
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valuable tool since it allows access to image/configuration files before
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eMMC or other NV media are available.
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There are two main ARM virtual Fixed Virtual Platform (FVP) models,
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`Versatile Express (VE) FVP and BASE FVP
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<http://www.arm.com/products/tools/models/fast-models/foundation-model.php>`_.
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The initial vexpress64 u-boot board created here runs on the VE virtual
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platform using the license-free Foundation_v8 simulator. Fortunately,
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the Foundation_v8 simulator also supports the BASE_FVP model which
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companies can purchase licenses for and contain much more functionality.
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So we can, in U-Boot, run either model by either using the VE FVP (default),
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or turning on ``CONFIG_BASE_FVP`` for the more full featured model.
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Rather than create a new armv8 board similar to ``armltd/vexpress64``, add
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semihosting calls to the existing one, enabled with ``CONFIG_SEMIHOSTING``
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and ``CONFIG_BASE_FVP`` both set. Also reuse the existing board config file
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vexpress_aemv8.h but differentiate the two models by the presence or
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absence of ``CONFIG_BASE_FVP``. This change is tested and works on both the
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Foundation and Base fastmodel simulators.
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QEMU
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^^^^
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Another ARM emulator which supports semihosting is `QEMU
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<https://www.qemu.org/>`_. To enable semihosting, enable
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``CONFIG_SERIAL_PROBE_ALL`` when configuring U-Boot, and use
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``-semihosting`` when invoking QEMU. Adding ``-nographic`` can also be
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helpful. When using a semihosted serial console, QEMU will block waiting
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for input. This will cause the GUI to become unresponsive. To mitigate
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this, try adding ``-nographic``. For more information about building and
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running QEMU, refer to the :doc:`board documentation
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<../board/emulation/qemu-arm>`.
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OpenOCD
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^^^^^^^
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Any ARM platform can use semihosting with an attached debugger. One such
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debugger with good support for a variety of boards and JTAG adapters is
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`OpenOCD <https://openocd.org/>`_. Semihosting is not enabled by default,
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so you will need to enable it::
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$ openocd -f <your board config> -c init -c halt -c \
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'arm semihosting enable' -c resume
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Note that enabling semihosting can only be done after attaching to the
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board with ``init``, and must be done while the CPU is halted. For a more
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extended example, refer to the :ref:`LS1046ARDB docs <ls1046ardb_jtag>`.
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Loading files
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-------------
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The semihosting code adds a "semihosting filesystem"::
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load hostfs - <address> <image>
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That will load an image from the host filesystem into RAM at the specified
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address. If you are using U-Boot SPL, you can also use ``BOOT_DEVICE_SMH``
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which will load ``CONFIG_SPL_FS_LOAD_PAYLOAD_NAME``.
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Host console
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------------
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U-Boot can use the host's console instead of a physical serial device by
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enabling ``CONFIG_SERIAL_SEMIHOSTING``. If you don't have
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``CONFIG_DM_SERIAL`` enabled, make sure you disable any other serial
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drivers.
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Migrating from ``smhload``
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--------------------------
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If you were using the ``smhload`` command, you can migrate commands like::
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smhload <file> <address> [<end var>]
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to a generic load command like::
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load hostfs - <address> <file>
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The ``load`` command will set the ``filesize`` variable with the size of
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the file. The ``fdt chosen`` command has been updated to take a size
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instead of an end address. If you were adding the initramfs to your device
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tree like::
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fdt chosen <address> <end var>
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you can now run::
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fdt chosen <address> $filesize
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