mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-11-19 11:18:28 +00:00
55 lines
2.5 KiB
Text
55 lines
2.5 KiB
Text
|
/*
|
||
|
|
* 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.
|