| .. 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. |