带你看u-boot源码里的README-第一部分

学习嵌入式中的bootloader时，最常用的就是u-boot了，u-boot一般都是稍微修改或者不改就能用。

但是作为一个非常非常优秀的单片机程序，我认为还是有必要深入学习u-boot。

读一读源码中的README，受益匪浅，部分英语不好的朋友，可以跟着我的文章一起看看README。

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Summary:简介:
========

This directory contains the source code for U-Boot, a boot loader for
Embedded boards based on PowerPC, ARM, MIPS and several other
processors, which can be installed in a boot ROM and used to
initialize and test the hardware or to download and run application
code.该目录包含U-Boot的源代码，U-Boot是基于PowerPC、ARM、MIPS和其他几个处理器的嵌入式板的引导加载程序，可以安装在引导ROM中，用于初始化和测试硬件，或下载和运行应用程序代码。

The development of U-Boot is closely related to Linux: some parts of
the source code originate in the Linux source tree, we have some
header files in common, and special provision has been made to
support booting of Linux images.U-Boot的开发与Linux密切相关:部分源代码来源于Linux源代码树，我们有一些共同的头文件，并且做了专门的规定来支持Linux映像的引导。

Some attention has been paid to make this software easily
configurable and extendable. For instance, all monitor commands are
implemented with the same call interface, so that it's very easy to
add new commands. Also, instead of permanently adding rarely used
code (for instance hardware test utilities) to the monitor, you can
load and run it dynamically.为了使该软件易于配置和扩展，本文做了一些工作。例如，所有监视器命令都使用相同的调用接口实现，因此很容易添加新命令。另外，您可以动态加载并运行它，而不是永久地向监视器添加很少使用的代码(例如硬件测试实用程序)。

Status:状态:
=======

In general, all boards for which a configuration option exists in the
Makefile have been tested to some extent and can be considered
"working". In fact, many of them are used in production systems.一般来说，所有在Makefile中存在配置选项的板子都经过了某种程度的测试，可以认为是“工作”的。事实上，它们中的许多被用于生产系统。

In case of problems see the CHANGELOG and CREDITS files to find out
who contributed the specific port.如果出现问题，请查看CHANGELOG和CREDITS文件，以找出谁贡献了特定的端口。

Where to get help:从哪里获得帮助:
==================

In case you have questions about, problems with or contributions for
U-Boot you should send a message to the U-Boot mailing list at
<[e-mail]>. There is also an archive of
previous traffic on the mailing list - please search the archive
before asking FAQ's. Please see
http://lists.sourceforge.net/lists/listinfo/u-boot-users/

如果你对U-Boot有疑问、问题或贡献，你应该向U-Boot邮件列表<[e-mail]>发送消息。在邮件列表中也有一个以前的流量存档-请在问FAQ(常问的问题)之前搜索存档。请参见http://lists.sourceforge.net/lists/listinfo/u-boot-users/

Where we come from:我们来自哪里:
===================

- start from 8xxrom sources-从8xxrom源开始创建
- create PPCBoot project (http://sourceforge.net/projects/ppcboot)PPCBoot项目(http://sourceforge.net/projects/ppcboot)
- clean up code清理代码
- make it easier to add custom boards-使它更容易添加定制板
- make it possible to add other [PowerPC] CPUs
- extend functions, especially:-允许添加其他[PowerPC] cpu扩展功能，特别是:
  * Provide extended interface to Linux boot loader*提供Linux引导加载程序的扩展接口
  * S-Record downloadS-Record​​​​​​​文件的下载
  * network boot网络引导
  * PCMCIA / CompactFLash / ATA disk / SCSI ... bootPCMCIA / CompactFLash / ATA磁盘/ SCSI…引导
- create ARMBoot project (http://sourceforge.net/projects/armboot)创建ARMBoot项目
- add other CPU families (starting with ARM)添加其他CPU系列(从ARM开始)
- create U-Boot project (http://sourceforge.net/projects/u-boot)创建U-Boot项目

Names and Spelling:名称和拼写:
===================

The "official" name of this project is "Das U-Boot". The spelling
"U-Boot" shall be used in all written text (documentation, comments
in source files etc.). Example:这个项目的“官方”名称是“Das U-Boot”。拼写“U-Boot”应使用在所有书面文本(文档，源文件中的注释等)。例子:

    This is the README file for the U-Boot project.

File names etc. shall be based on the string "u-boot". Examples:这是U-Boot项目的README文件。文件名等应基于字符串“u-boot”。例：

    include/asm-ppc/u-boot.h

    #include <asm/u-boot.h>

Variable names, preprocessor constants etc. shall be either based on
the string "u_boot" or on "U_BOOT". Example:变量名、预处理器常量等必须基于字符串“u_boot”或“u_boot”。例子:

    U_BOOT_VERSION        u_boot_logo
    IH_OS_U_BOOT        u_boot_hush_start

Versioning:版本控制:
===========

U-Boot uses a 3 level version number containing a version, a
sub-version, and a patchlevel: "U-Boot-2.34.5" means version "2",
sub-version "34", and patchlevel "4".U-Boot使用3级版本号，包括版本号、子版本号和补丁级别:“U-Boot-2.34.5”表示版本2、子版本34、补丁级别4。

The patchlevel is used to indicate certain stages of development
between released versions, i. e. officially released versions of
U-Boot will always have a patchlevel of "0".补丁级别用来表示发布版本之间的某个开发阶段，即U-Boot的官方发布版本总是会有一个“0”的补丁级别。

Directory Hierarchy:目录层次结构:
====================

- board        Board dependent files单板依赖文件
- common    Misc architecture independent functions通用异构架构独立功能
- cpu        CPU specific filesCPU专用文件
  - 74xx_7xx    Files specific to Freescale MPC74xx and 7xx CPUs飞思卡尔MPC74xx和7xx CPUsarm720t ARM 720专用文件
  - arm720t    Files specific to ARM 720 CPUs
  - arm920t    Files specific to ARM 920 CPUs
    - at91rm9200 Files specific to Atmel AT91RM9200 CPU
    - imx    Files specific to Freescale MC9328 i.MX CPUs
    - s3c24x0    Files specific to Samsung S3C24X0 CPUs
  - arm925t    Files specific to ARM 925 CPUs
  - arm926ejs    Files specific to ARM 926 CPUs
  - arm1136    Files specific to ARM 1136 CPUs
  - at32ap    Files specific to Atmel AVR32 AP CPUs
  - i386    Files specific to i386 CPUs
  - ixp        Files specific to Intel XScale IXP CPUs
  - mcf52x2    Files specific to Freescale ColdFire MCF52x2 CPUs
  - mips    Files specific to MIPS CPUs
  - mpc5xx    Files specific to Freescale MPC5xx  CPUs
  - mpc5xxx    Files specific to Freescale MPC5xxx CPUs
  - mpc8xx    Files specific to Freescale MPC8xx  CPUs
  - mpc8220    Files specific to Freescale MPC8220 CPUs
  - mpc824x    Files specific to Freescale MPC824x CPUs
  - mpc8260    Files specific to Freescale MPC8260 CPUs
  - mpc85xx    Files specific to Freescale MPC85xx CPUs
  - nios    Files specific to Altera NIOS CPUs
  - nios2    Files specific to Altera Nios-II CPUs
  - ppc4xx    Files specific to AMCC PowerPC 4xx CPUs
  - pxa        Files specific to Intel XScale PXA CPUs
  - s3c44b0    Files specific to Samsung S3C44B0 CPUs
  - sa1100    Files specific to Intel StrongARM SA1100 CPUs
- disk        Code for disk drive partition handling磁盘驱动器分区处理代码
- doc        Documentation (don't expect too much)文档(不要期望太多)
- drivers    Commonly used device drivers常用的设备驱动程序
- dtt        Digital Thermometer and Thermostat drivers数字温度计和温控器驱动器
- examples    Example code for standalone applications, etc.独立应用程序的示例代码，等
- include    Header Files包含头文件
- lib_arm    Files generic to ARM     architectureARM架构通用文件
- lib_avr32    Files generic to AVR32     architectureVR32架构通用文件
- lib_generic    Files generic to all     architectures
- lib_i386    Files generic to i386     architecture
- lib_m68k    Files generic to m68k     architecture
- lib_mips    Files generic to MIPS     architecture
- lib_nios    Files generic to NIOS     architecture
- lib_ppc    Files generic to PowerPC architecture
- net        Networking code网络代码-
- post        Power On Self Test上电自检
- rtc        Real Time Clock drivers实时时钟驱动程序
- tools        Tools to build S-Record or U-Boot images, etc.建立S-Record或U-Boot映像的工具

Software Configuration:软件配置:
=======================

Configuration is usually done using C preprocessor defines; the
rationale behind that is to avoid dead code whenever possible.配置通常使用C预处理器定义完成;其背后的基本原理是尽可能避免死代码。

There are two classes of configuration variables:有两类配置变量:

* Configuration _OPTIONS_:
  These are selectable by the user and have names beginning with
  "CONFIG_".用户可以选择它们，名称以“CONFIG”开头。

* Configuration _SETTINGS_:
  These depend on the hardware etc. and should not be meddled with if
  you don't know what you're doing; they have names beginning with
  "CFG_".这些取决于硬件等，如果你不知道自己在做什么，就不应该干预;它们的名字以“CFG_”开头。

Later we will add a configuration tool - probably similar to or even
identical to what's used for the Linux kernel. Right now, we have to
do the configuration by hand, which means creating some symbolic
links and editing some configuration files. We use the TQM8xxL boards
as an example here.稍后我们将添加一个配置工具—可能与Linux内核使用的配置工具类似，甚至相同。现在，我们必须这么做手动进行配置，这意味着创建一些符号链接和编辑一些配置文件。这里我们以TQM8xxL板为例。

Selection of Processor Architecture and Board Type:处理器架构和单板类型的选择:
---------------------------------------------------

For all supported boards there are ready-to-use default
configurations available; just type "make <board_name>_config".对于所有支持的板，都有现成的默认配置可用;只需输入“make <board_name>_config”。

Example: For a TQM823L module type:示例:对于TQM823L模块类型:

    cd u-boot
    make TQM823L_config

For the Cogent platform, you need to specify the cpu type as well;
e.g. "make cogent_mpc8xx_config". And also configure the cogent
directory according to the instructions in cogent/README.对于Cogent平台，您还需要指定cpu类型;如。“使cogent_mpc8xx_config”。并根据cogent/README中的说明配置cogent目录。