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diff --git a/doc/usage/semihosting.rst b/doc/usage/semihosting.rst new file mode 100644 index 0000000000..ed16e4d582 --- /dev/null +++ b/doc/usage/semihosting.rst @@ -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. |