Linux系统移植实战：从Bootloader到交叉工具链

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"《Linux系统移植》教程是针对嵌入式领域的书籍，专注于ARM架构下的Linux系统移植。书中详细介绍了从硬件环境到软件环境的设置，包括主机和目标板的硬件配置、各种必要的软件工具，如Windows和Linux操作系统，以及在Linux环境下进行交叉工具链的安装和配置。此外，还涵盖了tftp服务器的配置、minicom等工具的使用。书的作者团队对各个关键部分有深入的讲解，涉及ADS引导加载器、交叉工具、u-boot、内核、应用程序、网卡驱动和NandFlash驱动的移植。在系统启动部分，书中详细阐述了bootloader的编写，特别提到了ADS工具的使用，包括armasm、armcc、armcpp和armlink等命令行工具的介绍。深入讲解了可执行文件的内存映射、装载过程和启动流程，帮助读者理解从汇编到C语言的启动过程。AXD的使用方法也得到了详细介绍，包括如何配置仿真器和启动AXD以支持开发板。在GNU交叉工具链部分，读者将学习如何设置环境变量，准备各种源码包如binutils、gcc、glibc和linuxkernel，并应用相关补丁来构建适合ARM平台的交叉编译工具链。这一部分对于进行Linux系统移植至关重要，因为正确的工具链能够确保代码在目标硬件上正确编译和运行。《Linux系统移植》教程是一本全面且深入的指南，旨在帮助读者掌握在ARM平台上移植和定制Linux系统的技能，覆盖了从硬件准备到软件配置，再到系统组件的移植和调试的全过程。无论是对于初学者还是有经验的开发者，都能从中获得宝贵的知识和实践经验。"

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| .data | RW 段

+-------------+-----------

| .rodata |

| | 代码段 (RO 段 )

| .text |

+-------------+-----------

| ... |

装载前

当可执行文件装载后 , 在 RAM 中的分布如下：

| ... |

+-------------+-- ZI 段结束地址

| ZI 段 |

+-------------+-- ZI 段起始地址

| 保留区 2 |

+-------------+-- RW 段结束地址

| RW 段 |

+-------------+-- RW 段起始地址

| 保留区 1 |

+-------------+-- RO 段结束地址

| RO 段 |

+-------------+-- RO 段起始地址

| ... |

装载后

所以装载过程必须完成把执行文件的各个段从存储介质上搬到 RAM 指定的位置。而这个装载过程由谁来完

成呢？由我们的启动程序来完成 .

2 .

. 1.2

1.2

装载过程

在 ADS 中 , 可以通过两种方式来指定可执行代码各段在 RAM 中的位置 , 一个是用 armlink 来指定 , 一种是

用 scatter 文件来指定 .RAM 区的起始地址 :0x30000000.

1. armlink 指定代码段地址

我们通常的代码 , 只用指定两个段开始地址 , RO 段的起始地址和 RW 段的起始地址 , ZI 段紧接在 RW 段之

后 . 示例见该部分的 1.1.3.

2. scatter 指定代码段地址

我们也可以通过 scatter 文件指定可执行文件各段的详细地址 . Scatter 文件如下 :

M YLOADER 0x30000000

; M Y LOADER: 为可执行文件的名称 , 可自定义

;0x3000000: 起始地址

{

RO 0x30000000

;RO 只读代码段的名称

;0x30000000: 只读代码段的起始地址

{

init.o ( Init, + F i r st)

; In i t 代码段为可执行文件的第一部分 .

* ( + RO) ; 所有其它的代码段和只读数据段放在该部分

}

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RW + 0

;R W : RW 段的名称

; + 0: 表示 RW 段紧接着 RO 段

{

* ( + R W ) ; 所有 RW 段放在该部分

}

ZI + 0

;ZI: ZI 段的名称

; + 0: 表示 ZI 段紧接着 RW 段

{

* ( + ZI) ; 所有 ZI 段放在该部分

}

3. ADS 产生的各代码段宏

|Im a g e $$RO$$B a s e | /* RO 代码段起始地址 */

|Im a g e $$RO$$Limit| / * R O 代码段结束地址 */

|Im a g e $$R W $$ B a s e | /* RW 代码段起始地址 */

|Im a g e $$R W $$ L i mit| /* RW 代码段结束地址 */

|Im a g e $$ZI$$B a s e | /* ZI 代码段起始地址 */

|Im a g e $$ZI$$Lim i t| /* ZI 代码段结束地址 */

注意 : 在两个 $$ 之间的名称 , 与 s c a tt e r 中指定的段的名称相同 .

4. 装载过程说明

当从 No r F l a sh 启动时 , 要把 f l a sh 芯片的首地址映射到 0x00000000 位置 , 系统启动后 , 启动程序本身把自己从

f l a sh 中搬到 RAM 中运行 . 搬移后的各段起始地址 , 由以上宏来确定 .

当从 N a nd F l a sh 启动时 , S 3 C 2410 会自动把前 N a nd F l a sh 的前 4k 搬到 S 3 C 2410 的内部 R A M 中 , 并把内部

R A M 的首地址设为 0x00000000 ， C PU 从 0x00000000 开始执行 . 所以 , 在 n a nd F l a sh 的前 4k 程序中 , 必须包含从

N a nd F l a sh 把 BootLo a d e r 的其余部分装入 R A M 的程序 .

2 .

. 1.3

1.3

启动过程的汇编部分

当系统启动时 , A R M C PU 会跳到 0x00000000 去执行。一般 BootLo a d e r 都包括如下几个部分：

1. 建立中断向量异常表

2. 显示的切换到 S VC 且 32 指令模式

3. 关闭 S 3 C 2410 的内部看门狗

4. 禁止所有的中断

5. 配置系统时钟频率和总线频率

6. 设置内存区的控制寄存器

7. 初始化中断

8. 安装中断向表量

9. 把可执行文件的各个段搬到运行态的各个位置

10. 跳到 C 代码部分执行

2 .

. 1.4

1.4

启动过程的

部分

1. 初始化 M M U

2. 初始化外部端口

3. 中断处理程序表初始化

4. 串口初始化

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微软 ARM 联合认证嵌入式合作伙伴

5. 其它部分初始化 ( 可选 )

6. 主程序循环

3 A

A X

X D

的使用以及源代码说明

3.1

3.1 源代码说明

3 .

. 1.1

1.1

汇编源代码说明

; = === = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = =

; 引用头文件

; = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = =

g et b di n i t .h

; = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = =

; 引用标准变量

; = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = =

IMPORT |Ima

e$$RO$$Base| ; Base address

f RO sec

i o n

IMPORT |Ima

e$$RO$$Limi

| ;

n d address

f RO sec

i o n

IMPORT |Ima

e$$RW$$Base| ; Base address

f RW sec

i o n

IMPORT |Ima

e$$RW$$Limi

| ;

n d address

f RW sec

i o n

IMPORT |Ima

e$$ZI$$Base| ; Base address

f ZI sec

i o n

IMPORT |Ima

e$$ZI$$Limi

| ;

n d addresss

f ZI sec

i o n

IMPORT

dmain ; T

e e

t ry fu

c t i o n o f C pr

g ram

; = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = =

; 宏定义

; = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = =

; macro HA

DL E R

MACRO

$Ha

dlerLa

el HA

DL E R $Ha

dleLa

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ldr r0,=$Ha

dleLa

el;L

h e address

f Ha

dleXXX

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; = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = =

; 汇编语言的入口代码

; = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = == = = = = = == = = = =

AR E A I

i t ,COD

,R E ADO

COD

EN TRY

;=====================

; 建立中断向量表

;=====================

sub

sp,sp,#4

;Decreme

t sp (

o s t o re jump address)

s t mfd

sp!,

{

r0}

;PU

H t h e w o rk re

is t er

o s t ack

ldr

r0,[r0]

h e c

nt e nt s(service r

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dleXXX

s t r

r0,[sp,#4]

;

to re

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ldmfd

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{

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;POP

h e w o rk re

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o I S R)

M E N D

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