projects / u-boot.git / blame
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| 261d2760 DR |
1 | /* |
| 2 | * Copyright 2014 Broadcom Corporation. | |
| 3 | * | |
| 4 | * SPDX-License-Identifier: GPL-2.0+ | |
| 5 | */ | |
| 6 | ||
| 7 | Semihosting is ARM's way of having a real or virtual target communicate | |
| 8 | with a host or host debugger for basic operations such as file I/O, | |
| 9 | console I/O, etc. Please see | |
| 10 | http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0471c/Bgbjjgij.html for more information. | |
| 11 | ||
| 12 | For developing on armv8 virtual fastmodel platforms, semihosting is a | |
| 13 | valuable tool since it allows access to image/configuration files before | |
| 14 | eMMC or other NV media are available. | |
| 15 | ||
| 16 | There are two main ARM virtual Fixed Virtual Platform (FVP) models, | |
| 17 | Versatile Express (VE) FVP and BASE FVP (See | |
| 18 | http://www.arm.com/products/tools/models/fast-models/foundation-model.php) | |
| 19 | The initial vexpress64 u-boot board created here runs on the VE virtual | |
| 20 | platform using the license-free Foundation_v8 simulator. Fortunately, | |
| 21 | the Foundation_v8 simulator also supports the BASE_FVP model which | |
| 22 | companies can purchase licenses for and contain much more functionality. | |
| 23 | So we can, in u-boot, run either model by either using the VE FVP (default), | |
| 24 | or turning on CONFIG_BASE_FVP for the more full featured model. | |
| 25 | ||
| 26 | Rather than create a new armv8 board similar to armltd/vexpress64, add | |
| 27 | semihosting calls to the existing one, enabled with CONFIG_SEMIHOSTING | |
| 28 | and CONFIG_BASE_FVP both set. Also reuse the existing board config file | |
| 29 | vexpress_aemv8a.h but differentiate the two models by the presence or | |
| 30 | absence of CONFIG_BASE_FVP. This change is tested and works on both the | |
| 31 | Foundation and Base fastmodel simulators. | |
| 32 | ||
| 33 | The level of semihosting support is minimal, restricted to just what it | |
| 34 | takes to load images to memory. If more semihosting functionality is | |
| 35 | required, such as file seek, outputting strings, reading characters, etc, | |
| 36 | then it can be easily added later. | |
| 37 | ||
| 38 | We require that the board include file define these env variables: | |
| 39 | - kernel_name e.g. "uImage" | |
| 40 | - kernel_addr_r e.g. "0x80000000" | |
| 41 | - initrd_name e.g. "ramdisk.img" | |
| 42 | - initrd_addr_r e.g. "0x88000000" | |
| 43 | - fdt_name e.g. "devtree.dtb" | |
| 44 | - fdt_addr_r e.g. "0x83000000" | |
| 45 | ||
| 46 | Optionally, "fdt_high" and "initrd_high" can be specified as per | |
| 47 | their rules for allowing or preventing copying of these images. | |
| 48 | ||
| 49 | For the "fdt chosen" startup macro, this code will then define: | |
| 50 | - initrd_end (based on retrieving initrd_addr_r plus actual initrd_size) | |
| 51 | ||
| 52 | We will then load the kernel, initrd, and fdt into the specified | |
| 53 | locations in memory in a similar way that the ATF fastmodel code | |
| 54 | uses semihosting calls to load other boot stages and u-boot itself. |