123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354 |
- /*
- * Copyright 2014 Broadcom Corporation.
- *
- * SPDX-License-Identifier: GPL-2.0+
- */
- 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
- http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0471c/Bgbjjgij.html 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 (See
- 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_aemv8a.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.
- The level of semihosting support is minimal, restricted to just what it
- takes to load images to memory. If more semihosting functionality is
- required, such as file seek, outputting strings, reading characters, etc,
- then it can be easily added later.
- We require that the board include file define these env variables:
- - kernel_name e.g. "uImage"
- - kernel_addr_r e.g. "0x80000000"
- - initrd_name e.g. "ramdisk.img"
- - initrd_addr_r e.g. "0x88000000"
- - fdt_name e.g. "devtree.dtb"
- - fdt_addr_r e.g. "0x83000000"
- Optionally, "fdt_high" and "initrd_high" can be specified as per
- their rules for allowing or preventing copying of these images.
- For the "fdt chosen" startup macro, this code will then define:
- - initrd_end (based on retrieving initrd_addr_r plus actual initrd_size)
- We will then load the kernel, initrd, and fdt into the specified
- locations in memory in a similar way that the ATF fastmodel code
- uses semihosting calls to load other boot stages and u-boot itself.
|