查看“U-Boot overview”的源代码

== Das U-Boot ==
[https://en.wikipedia.org/wiki/Das_U-Boot Das U-Boot] (“通用引导加载程序”或U-Boot) 是一种开源引导加载程序，可用于ST板上以初始化平台并加载Linux<sup>&reg;</sup> 内核。

* 官方网站： [https://www.denx.de/wiki/U-Boot https://www.denx.de/wiki/U-Boot]
* 官方手册： [http://www.denx.de/wiki/U-Boot/Documentation|U-Boot project documentation] 和 [https://www.denx.de/wiki/DULG/Manual https://www.denx.de/wiki/DULG/Manual]
* 官方的[https://www.denx.de/wiki/U-Boot/SourceCode '''源代码'''] 可在 [https://git-scm.com/ git] 存储库下找到[https://gitlab.denx.de/u-boot/u-boot]
  {{PC$}} git clone https://gitlab.denx.de/u-boot/u-boot.git

在开始使用U-Boot之前，请阅读{{CodeSource | U-Boot | README | README file}}。它涵盖以下主题：
* 源文件树结构
* 配置定义说明
* 关于构建U-Boot的说明
* Hush外壳的简要说明
* 常用环境变量列表

== U-Boot overview ==
[[File: STM32MPU Embedded Software architecture overview.png|link=STM32MPU Embedded Software architecture overview|thumb|Zoom out to STM32MPU Embedded Software]]
同一个U-Boot源可以生成SPL和U-Boot中使用的两个固件 [[Boot_chains_overview#STM32MP boot chains|STM32 MPU boot chain]]:
* 受信任的引导链：TF-A作为FSBL，U-Boot作为SSBL
* 基本启动链：SPL作为FSBL，U-Boot作为SSBL

<br clear=all>

{{Warning | 基本启动链不能用于产品开发 (请参见[[Boot_chains_overview#Boot_chains_features_set|Boot chains 
overview]] 以获取详细信息).}} 
它仅作为最简单的SSBL的示例提供，并支持上游U-Boot开发。但是，当SPL与U-Boot中提供的用于基本引导链的最小安全监视器结合使用时，已经发现了几个已知的限制。它们适用于:
* 功率
* 安全访问寄存器
* 有限的功能(STM32CubeProgrammer / boot from NAND Flash memory). 
没有针对这些限制的修复计划。

=== SPL: FSBL for basic boot===
'''U-Boot SPL''' 或 '''SPL''' 是 [[Boot_chains_overview#STM32MP boot chains|the basic boot chain]]的第一阶段引导加载程序（FSBL）。<br/>它是从U-Boot源生成的小二进制文件（引导实用程序），并存储在内部有限大小的嵌入式RAM中。SPL的主要功能如下：
* 它由ROM代码加载。
* 它执行初始的CPU和板配置（时钟和DDR内存）。
* 它将SSBL(U-Boot)加载到DDR内存中。

=== U-Boot: SSBL ===
'''U-Boot''' 是STM32 MPU平台的默认第二阶段引导程序（SSBL）。它同时用于 [[Boot_chains_overview#STM32MP boot chains|trusted and basic]]引导链

SSBL的主要功能如下：
* 它是可配置和消耗的。
* 它具有一个简单的命令行界面（CLI），允许用户通过串行端口控制台进行交互。
* 它提供脚本功能
* 它将内核加载到RAM中并控制内核
* 它管理多个内部和外部设备，例如NAND和NOR闪存，以太网和USB。
* 它支持以下功能和命令：
** 文件系统：FAT, UBI/UBIFS, JFFS
** IP堆栈：FTP
** 显示： LCD, HDMI, BMP for splashcreen
** USB: host (mass storage) or device (DFU stack)

=== SPL phases ===
'''SPL''' 在SYSRAM中执行以下主要阶段：
* '''board_init_f()''': 驱动程序初始化，包括DDR初始化（最小堆栈和堆：CONFIG_SPL_STACK_R_MALLOC_SIMPLE_LEN）
* DDR内存中堆的配置(CONFIG_SPL_SYS_MALLOC_F_LEN)
* '''board_init_r()''': 初始化在SPL设备树中激活的其他驱动程序
* 加载并执行U-Boot(或Falcon模式下的内核<ref>https://www.denx.de/wiki/pub/U-Boot/MiniSummitELCE2013/2013-ELCE-U-Boot-Falcon-Boot.pdf</ref>: {{CodeSource | U-Boot | doc/README.falcon | README.falcon }}).

=== U-Boot phases ===
'''U-Boot''' 在DDR内存中执行以下主要阶段：
* '''Pre-relocation''' 初始化 (common/board_f.c): 在CONFIG_SYS_TEXT_BASE加载地址上运行的最小初始化（例如CPU，时钟，重置，DDR和控制台）
* '''Relocation''': 将代码复制到DDR内存的末尾。
* '''Post-relocation initialization''':(common/board_r.c): 初始化所有驱动程序。
* '''Command execution''' 通过自动引导(CONFIG_AUTOBOOT)或控制台shell
** 启动命令的执行（默认情况下[[#bootcmd | bootcmd=CONFIG_BOOTCOMMAND]]）：<br/>例如，将命令<code>bootm</code>执行到：
*** 加载并检查映像（例如内核，设备树和ramdisk）
*** 修复内核设备树
*** 安装安全监视器（可选）或
*** 将控制权传递给Linux内核(或另一个目标应用程序)

== U-Boot configuration ==
U-Boot二进制配置基于
* '''Kbuild infrastructure''' (与[[Menuconfig_or_how_to_configure_kernel|Linux Kernel]], 您可以在U-Boot中使用<code>make menuconfig</code> )<br/>配置基于以下各项：
** 在 Kconfig 文件中定义的选项(CONFIG _ compilation 标志)
** 所选配置文件：{{CodeSource | U-Boot | configs/ | configs/stm32mp*_defconfig}}<br/>
* '''other compilation flags''' 定义于{{CodeSource | U-Boot | include/configs/ | include/configs/stm32mp*.h}}  (这些标志将逐步迁移到Kconfig)<br/>文件名通过CONFIG_SYS_CONFIG_NAME配置。<br/>对于 {{MicroprocessorDevice | device=15}}, 使用了{{CodeSource | U-Boot | include/configs/stm32mp1.h | include/configs/stm32mp1.h}}文件。

* '''[[Device_tree|DeviceTree]]''': U-Boot和SPL二进制文件包括在运行时解析的设备树blob
所有的配置标志(前缀为 CONFIG_)都在源代码中描述， 或者在 {{CodeSource | U-Boot | README | README}} 文件中，或者在{{CodeSource | U-Boot | doc/ | documentation directory}}目录中。<br/>例如，CONFIG_SPL激活SPL编译<br />
因此，为了选择一个预定义的配置，需要为主板编译 U-Boot，[[#Kbuild|select the <target>]] 和 [[#Device_tree|the device tree]] 。<br/>
有关示例，请参阅[[#U-Boot_build]]。

=== Kbuild ===

与内核一样，U-Boot构建系统也基于 [[Menuconfig_or_how_to_configure_kernel|configuration symbols]] (在Kconfig文件中定义). 选定的值存储在build目录的'''.config'''文件中，具有相同的Makefile目标。 <br/>
按照以下步骤进行:
* 选择预定义的配置({{CodeSource | U-Boot | configs/ | configs directory }}中的defconfig文件) 并生成第一个 '''.config''':
  {{PC$}} make <config>_defconfig.

* 使用以下五个<code>make</code> 命令之一更改U-Boot编译配置(修改.config)：
  {{PC$}} '''make menuconfig''' {{Highlight|--> menu based program}}
  {{PC$}} make config  {{Highlight|--> line-oriented configuration}}
  {{PC$}} make xconfig {{Highlight|--> QT program<ref>https://en.wikipedia.org/wiki/Xconfig</ref>}}
  {{PC$}} make gconfig {{Highlight|--> GTK program}}
  {{PC$}} make nconfig {{Highlight|--> ncurse menu based program}}
然后，您可以使用更新的.config编译U-Boot。

Warning: 修改是在构建目录的本地执行的。在<code> make distclean 之后它将丢失</code>.

保存您的配置以将其用作defconfig文件：
   {{PC$}} make savedefconfig
此目标将当前配置保存为build目录中的defconfig文件。 然后可以将其与预定义的配置进行比较(configs/stm32mp*defconfig).

其他makefile目标如下：

   {{PC$}} make help
  ....
  Configuration targets:
    config	  - Update current config utilising a line-oriented program
    nconfig         - Update current config utilising a ncurses menu based
                      program
    menuconfig	  - Update current config utilising a menu based program
    xconfig	  - Update current config utilising a Qt based front-end
    gconfig	  - Update current config utilising a GTK+ based front-end
    oldconfig	  - Update current config utilising a provided .config as base
    localmodconfig  - Update current config disabling modules not loaded
    localyesconfig  - Update current config converting local mods to core
    defconfig	  - New config with default from ARCH supplied defconfig
    savedefconfig   - Save current config as ./defconfig (minimal config)
    allnoconfig	  - New config where all options are answered with no
    allyesconfig	  - New config where all options are accepted with yes
    allmodconfig	  - New config selecting modules when possible
    alldefconfig    - New config with all symbols set to default
    randconfig	  - New config with random answer to all options
    listnewconfig   - List new options
    olddefconfig	  - Same as oldconfig but sets new symbols to their
                     default value without prompting

=== Device tree ===
Refer to {{CodeSource | U-Boot | doc/README.fdt-control | doc/README.fdt-control}} for details.

The board device tree has the same binding as the kernel. It is integrated within the SPL and U-Boot binaries:
* By default, it is appended at the end of the code  (CONFIG_OF_SEPARATE).
* It is embedded in the U-Boot binary (CONFIG_OF_EMBED). This is useful for debugging since it enables easy .elf file loading.

A default device tree is available in the defconfig file (by setting CONFIG_DEFAULT_DEVICE_TREE).

You can either select another supported device tree using the DEVICE_TREE make flag. For stm32mp boards, the corresponding file is: {{CodeSource | U-Boot | arch/arm/dts/ | arch/arm/dts/stm32mp*.dts}}.
   {{PC$}} make DEVICE_TREE=<dts-file-name>

or provide a precompiled device tree blob (using EXT_DTB option):
   {{PC$}} make EXT_DTB=boot/<dts-file-name>.dtb

The SPL device tree is also generated from this device tree. However to reduce its size, the U-Boot makefile uses the fdtgrep tool to parse the full U-Boot DTB and identify all the drivers required by SPL.

To do this, U-Boot uses specific device-tree flags to define if the associated driver is initialized prior to U-Boot relocation and/or if the associated node is present in SPL :
* '''u-boot,dm-pre-reloc''' => present in SPL, initialized before relocation in U-Boot
* '''u-boot,dm-pre-proper''' => initialized before relocation in U-Boot
* '''u-boot,dm-spl''' => present in SPL

In the device tree used by U-Boot, these flags '''need to be added in each node''' used in SPL or in U-Boot before relocation and for each used handle (clock, reset, pincontrol).

== U-Boot command line interface (CLI) ==
Refer to [http://www.denx.de/wiki/view/DULG/UBootCommandLineInterface U-Boot Command Line Interface].

If CONFIG_AUTOBOOT is activated, you have CONFIG_BOOTDELAY seconds (2s by default) to enter the console by pressing any key, after the line below is displayed and [[#bootcmd|bootcmd]] is executed (CONFIG_BOOTCOMMAND):
  Hit any key to stop autoboot:  2

=== Commands ===
The commands are defined in {{CodeSource | U-Boot | cmd/ | cmd/*.c}}. They are activated through the corresponding '''CONFIG_CMD_*''' configuration flag.

Use the <code>help</code> command in the U-Boot shell to list the commands available on your device:
  {{Board$}} help

Below the list of all commands extracted from [http://www.denx.de/wiki/view/DULG/Manual U-Boot Manual] ('''not-exhaustive'''):
* [http://www.denx.de/wiki/view/DULG/UBootCmdGroupInfo Information Commands]
** bdinfo - prints Board Info structure
** coninfo - prints console devices and information
** flinfo - prints Flash memory information
** iminfo - prints header information for application image
** help - prints online help
* [http://www.denx.de/wiki/view/DULG/UBootCmdGroupMemory Memory Commands]
** base - prints or sets the address offset
** crc32 - checksum calculation
** cmp - memory compare
** cp - memory copy
** md - memory display
** mm - memory modify (auto-incrementing)
** mtest - simple RAM test
** mw - memory write (fill)
** nm - memory modify (constant address)
** loop - infinite loop on address range
* [http://www.denx.de/wiki/view/DULG/UBootCmdGroupFlash Flash Memory Commands]
** cp - memory copy
** flinfo - prints Flash memory information
** erase - erases Flash memory
** protect - enables or disables Flash memory write protection
** mtdparts - defines a Linux compatible MTD partition scheme
* [http://www.denx.de/wiki/view/DULG/UBootCmdGroupExec Execution Control Commands]
** source - runs a script from memory
** bootm - boots application image from memory
** go - starts application at address 'addr'
* [http://www.denx.de/wiki/view/DULG/UBootCmdGroupDownload Download Commands]
** bootp - boots image via network using BOOTP/TFTP protocol
** dhcp - invokes DHCP client to obtain IP/boot params
** loadb - loads binary file over serial line (kermit mode)
** loads - loads S-Record file over serial line
** rarpboot- boots image via network using RARP/TFTP protocol
** tftpboot- boots image via network using TFTP protocol
* [http://www.denx.de/wiki/view/DULG/UBootCmdGroupEnvironment Environment Variables Commands]
** printenv- prints environment variables
** saveenv - saves environment variables to persistent storage
** setenv - sets environment variables
** run - runs commands in an environment variable
** bootd - boots default, i.e., run 'bootcmd'
* [http://www.denx.de/wiki/view/DULG/UBootCmdFDT Flattened Device Tree support]
** fdt addr - selects the FDT to work on
** fdt list - prints one level
** fdt print - recursive printing
** fdt mknode - creates new nodes
** fdt set - sets node properties
** fdt rm - removes nodes or properties
** fdt move - moves FDT blob to new address
** fdt chosen - fixup dynamic information
* [http://www.denx.de/wiki/view/DULG/UBootCmdGroupSpecial Special Commands]
** i2c - I2C sub-system
* [http://www.denx.de/wiki/view/DULG/UBootStorageDevices Storage devices]
* [http://www.denx.de/wiki/view/DULG/UBootCmdGroupMisc Miscellaneous Commands]
** echo - echoes args to console
** reset - Performs a CPU reset  
** sleep - delays the execution for a predefined time 
** version - prints the monitor version

To add a new command, refer to {{CodeSource | U-Boot | doc/README.commands }}.

=== U-Boot environment variables ===

The U-Boot behavior is configured through environment variables.

Refer to [http://www.denx.de/wiki/view/DULG/UBootEnvVariables Manual] and {{CodeSource | U-Boot | README | README}} / Environment Variables.

On the first boot, U-Boot uses a default environment embedded in the U-Boot binary. You can modify it by changing the content of CONFIG_EXTRA_ENV_SETTINGS in your configuration file (for example ./include/configs/stm32mp1.h) (see {{CodeSource | U-Boot | README | README}} / - Default Environment).

This environment can be modified and saved in the boot device. When it is present, it is loaded during U-Boot initialization:
* for ''e''•MMC/SD card boot (CONFIG_ENV_IS_IN_EXT4), in the bootable ext4 partition "bootfs" in <br/>in file CONFIG_ENV_EXT4_FILE="uboot.env".
* for NAND boot (CONFIG_ENV_IS_IN_UBI), in the two UBI volumes "config" (CONFIG_ENV_UBI_VOLUME) and "config_r"  (CONFIG_ENV_UBI_VOLUME_REDUND).
* for NOR boot (CONFIG_ENV_IS_IN_SPI_FLASH), in the u-boot_env mtd parttion (at offset CONFIG_ENV_OFFSET).

==== env command ====

The <code>env</code> command allows displaying, modifying and saving the environment in U-Boot console.

  {{Board$}} help env
  env - environment handling commands
  
  Usage:
  env default [-f] -a - [forcibly] reset default environment
  env default [-f] var [...] - [forcibly] reset variable(s) to their default values
  env delete [-f] var [...] - [forcibly] delete variable(s)
  env edit name - edit environment variable
  env exists name - tests for existence of variable
  env print [-a | name ...] - print environment
  env print -e [name ...] - print UEFI environment
  env run var [...] - run commands in an environment variable
  env save - save environment
  env set -e name [arg ...] - set UEFI variable; unset if 'arg' not specified
  env set [-f] name [arg ...]

Example: proceed as follows to restore the default environment and save it. This is useful after a U-Boot upgrade:

  {{Board$}} env default -a
  {{Board$}} env save

==== bootcmd ====
"bootcmd" variable is the autoboot command. It defines the command executed when U-Boot starts (CONFIG_BOOTCOMMAND).

For stm32mp,  CONFIG_BOOTCOMMAND="run bootcmd_stm32mp":

  {{Board$}} env print bootcmd    
   bootcmd=run bootcmd_stm32mp

"bootcmd_stm32mp" is a script that selects the command to be executed for each boot device (see ./include/configs/stm32mp1.h), based on [[#Generic Distro configuration|generic distro scripts]]:
* for serial/usb: execute the <code>stm32prog</code> command.
* for mmc boot (''e''•MMC, SD card), boot only on the same device (bootcmd_mmc...).
* for nand boot, boot with on ubifs partition on nand (bootcmd_ubi0).
* for nor boot, use the default order ''e''•MMC (SDMMC 1)/ NAND / SD card (SDMMC 0) / SDMMC2 (the default bootcmd: distro_bootcmd).

  {{Board$}} env print bootcmd_stm32mp

You can then change this configuration:
* either permanently in your board file (default environment by CONFIG_EXTRA_ENV_SETTINGS or change CONFIG_BOOTCOMMAND value) or
* temporarily in the saved environment:

  {{Board$}} env set bootcmd run bootcmd_mmc0 
  {{Board$}} env save

Note: To reset the environment to its default value: 

  {{Board$}} env default bootcmd
  {{Board$}} env save

=== Generic Distro configuration ===

Refer to {{CodeSource | U-Boot | doc/README.distro | doc/README.distro}} for details.

This feature is activated by default on ST boards (CONFIG_DISTRO_DEFAULTS):
* one boot command (bootmcd_xxx) exists for each bootable device.
* U-Boot is independent of the Linux distribution used.
* bootcmd is defined in {{CodeSource | U-Boot | ./include/config_distro_bootcmd.h }}

When DISTRO is enabled, the command that is executed by default is {{CodeSource | U-Boot | include/config_distro_bootcmd.h}}:
  bootcmd=run distro_bootcmd

This script tries any device found in the 'boot_targets' variable and executes the associated bootcmd.

Example for mmc0, mmc1, mmc2, pxe and ubifs devices:
  bootcmd_mmc0=setenv devnum 0; run mmc_boot
  bootcmd_mmc1=setenv devnum 1; run mmc_boot
  bootcmd_mmc2=setenv devnum 2; run mmc_boot
  bootcmd_pxe=run boot_net_usb_start; dhcp; if pxe get; then pxe boot; fi
  bootcmd_ubifs0=setenv devnum 0; run ubifs_boot

U-Boot searches for a '''extlinux.conf''' configuration file for each bootable device. This file defines the kernel configuration to be used: 
* bootargs
* kernel + device tree + ramdisk files (optional)
* FIT image

=== U-Boot scripting capabilities ===

"Script files" are command sequences that are executed by the U-Boot command interpreter. This feature is particularly useful to configure U-Boot to use a real shell (hush) as command interpreter.

See [http://www.denx.de/wiki/view/DULG/UBootScripts| U-Boot script manual] for an example.

== U-Boot build ==
=== Prerequisites ===

* a PC with Linux and tools: 
** see [[PC_prerequisites]]
** [[#ARM cross compiler]]
* U-Boot source code
** the latest STMicroelectronics U-Boot version
*** tar.xz file from Developer Package (for example [[STM32MP1_Developer_Package#Installing_the_U-Boot|STM32MP1]])
*** from GITHUB<ref>https://github.com/STMicroelectronics/u-boot</ref>, with <code>git</code> command
  {{PC$}} git clone https://github.com/STMicroelectronics/u-boot
:* from the Mainline U-Boot in official GIT repository <ref>https://gitlab.denx.de/u-boot/u-boot.git or https://github.com/u-boot/u-boot</ref>
  {{PC$}} git clone https://gitlab.denx.de/u-boot/u-boot.git

==== ARM cross compiler ====

A cross compiler <ref>https://en.wikipedia.org/wiki/Cross_compiler</ref> must be installed on your Host (X86_64, i686, ...) for the ARM targeted Device architecture. In addition, the $PATH and $CROSS_COMPILE environment variables must be configured in your shell.

You can use gcc for ARM, available in:
* the SDK toolchain (see [[Cross-compile with OpenSTLinux SDK]])<br/>PATH and CROSS_COMPILE are automatically updated.
* an existing package<br/>For example, install gcc-arm-linux-gnueabihf on Ubuntu/Debian: ({{PC$}} sudo apt-get.
* an existing toolchain:
** latest gcc toolchain provided by arm (https://developer.arm.com/open-source/gnu-toolchain/gnu-a/downloads/)
** gcc v7 toolchain provided by linaro: (https://www.linaro.org/downloads/)

For example, to use ''gcc-arm-9.2-2019.12-x86_64-arm-none-linux-gnueabihf.tar.xz'' from arm, extract the toolchain in $HOME and update your environment with:
  {{PC$}} export PATH=$HOME/gcc-arm-9.2-2019.12-x86_64-arm-none-linux-gnueabihf/bin:$PATH
  {{PC$}} export CROSS_COMPILE=arm-none-linux-gnueabihf-

For example, to use '''gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabi.tar.xz'''<br/>from https://releases.linaro.org/components/toolchain/binaries/7.2-2017.11/arm-linux-gnueabi/<br/>
Unzip the toolchain in $HOME and update your environment with:
  {{PC$}} export PATH=$HOME/gcc-linaro-7.2.1-2017.11-x86_64_arm-linux-gnueabi/bin:$PATH
  {{PC$}} export CROSS_COMPILE=arm-linux-gnueabi-

=== Compilation  ===
In the U-Boot source directory, select the <target> and the <device tree> for your configuration and then execute the <code>make all</code> command:

  {{PC$}} make <target>_defconfig
  {{PC$}} make DEVICE_TREE=<device-tree> all

Optionally '''KBUILD_OUTPUT''' can be used to change the output directory to compile several targets or not to compile in the source directory. For example:
  {{PC$}} export KBUILD_OUTPUT=../build/basic

'''DEVICE_TREE''' can also be exported to your environment when only one board is supported. For example:
  {{PC$}} export DEVICE_TREE=stm32mp157c-ev1

Examples from [[STM32MP15 U-Boot]]:

Three configurations are supported for  {{MicroprocessorDevice | device=15}}:
* {{Highlight|stm32mp15_trusted_defconfig}}: [[Boot_chains_overview#STM32MP boot chains|trusted boot chain]], U-Boot (without SPL) is unsecure and uses Secure monitor from TF-A
* {{Highlight|stm32mp15_optee_defconfig}}: [[Boot_chains_overview#STM32MP boot chains|trusted boot chain]], U-Boot (without SPL) is unsecure and uses Secure monitor from SecureOS = [[OP-TEE overview|OP-TEE]]
* stm32mp15_basic_defconfig: [[Boot_chains_overview#STM32MP boot chains|basic boot chain]], with an SPL as FSBL, U-BOOT is secure and installs monitor with PSCI

The board diversity is only managed with the device tree.

  {{PC$}} export KBUILD_OUTPUT=../build/trusted
  {{PC$}} make stm32mp15_trusted_defconfig
  {{PC$}} make DEVICE_TREE=stm32mp157c-<board> all

  {{PC$}} export KBUILD_OUTPUT=../build/optee
  {{PC$}} export DEVICE_TREE=stm32mp157c-<board>
  {{PC$}} make stm32mp15_optee_defconfig
  {{PC$}} make all

  {{PC$}} make stm32mp15_basic_defconfig
  {{PC$}} make DEVICE_TREE=stm32mp157c-<board>  all

Use help to list other targets:
  {{PC$}} make help

=== Output files ===
The resulting U-Boot files are located in your build directory (U-Boot or KBUILD_OUTPUT).

Two binary formats are used for stm32mp devices:
* STM32 image format (*.stm32),  managed by mkimage U-Boot tools and [[Signing_tool]]. It is requested by ROM code and TF-A (see [[STM32 header for binary files]] for details).
* uImage (*.img) format, file including a U-Boot header, managed by SPL and U-Boot (for kernel load)

The U-Boot generated files are the following
* For {{Highlight|'''Trusted boot chain'''}} (TF-A is used as FSBL, with or without OP-TEE)
** {{Highlight|'''u-boot.stm32'''}} : U-Boot binary with STM32 image header, loaded by TF-A

* For '''Basic boot chain''' (SPL is used as FSBL)
** '''u-boot-spl.stm32''' : SPL binary with STM32 image header, loaded by ROM code
** '''u-boot.img''' : U-Boot binary with uImage header, loaded by SPL

The files used to debug with gdb are
* u-boot : elf file for U-Boot
* spl/u-boot-spl : elf file for SPL

== References ==
<references/>

<noinclude>
[[Category:U-Boot]]
{{PublicationRequestId | 12893 | 2019-08-01}}
</noinclude>