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doc: Convert semihosting readme to rST

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This converts the semihosting readme to rST. I have tried to make only
cosmetic changes, but I did fix up the first link (which was broken).

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
This commit is contained in:
Sean Anderson 2022-03-22 16:59:09 -04:00 • committed by Tom Rini
parent 8d78a6b674
commit d0ed9b1081
2 changed files with 21 additions and 15 deletions
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doc/usage/index.rst
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@ -11,6 +11,7 @@ Use U-Boot
netconsole
partitions
cmdline
semihosting
Shell commands
--------------

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doc/usage/semihosting.rst Normal file
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@ -0,0 +1,43 @@
.. SPDX-License-Identifier: GPL-2.0+
.. Copyright 2014 Broadcom Corporation.
Semihosting
===========
Semihosting is ARM's way of having a real or virtual target communicate
with a host or host debugger for basic operations such as file I/O,
console I/O, etc. Please see `Arm's semihosting documentation
<https://developer.arm.com/documentation/100863/latest/>`_ for more
information.
For developing on armv8 virtual fastmodel platforms, semihosting is a
valuable tool since it allows access to image/configuration files before
eMMC or other NV media are available.
There are two main ARM virtual Fixed Virtual Platform (FVP) models,
`Versatile Express (VE) FVP and BASE FVP
<http://www.arm.com/products/tools/models/fast-models/foundation-model.php>`_.
The initial vexpress64 u-boot board created here runs on the VE virtual
platform using the license-free Foundation_v8 simulator. Fortunately,
the Foundation_v8 simulator also supports the BASE_FVP model which
companies can purchase licenses for and contain much more functionality.
So we can, in U-Boot, run either model by either using the VE FVP (default),
or turning on ``CONFIG_BASE_FVP`` for the more full featured model.
Rather than create a new armv8 board similar to ``armltd/vexpress64``, add
semihosting calls to the existing one, enabled with ``CONFIG_SEMIHOSTING``
and ``CONFIG_BASE_FVP`` both set. Also reuse the existing board config file
vexpress_aemv8.h but differentiate the two models by the presence or
absence of ``CONFIG_BASE_FVP``. This change is tested and works on both the
Foundation and Base fastmodel simulators.
Loading files
-------------
The semihosting code adds a "hostfs"::
smhload <image> <address> [env var]
That will load an image from the host filesystem into RAM at the specified
address and optionally store the load end address in the specified
environment variable.