ARM 启动代码分析

 ;=========================================

; NAME: 2440INIT.S

; DESC: C start up codes

; Configure memory, ISR ,stacks

;Initialize C-variables

; HISTORY:

; 2002.02.25:kwtark: ver 0.0

; 2002.03.20:purnnamu: Add some functions for testing STOP,Sleep

GET option.inc ;芯片相关配置定义

GET memcfg.inc ;存储器配置定义

GET 2440addr.inc ;寄存器地址定义

;用于节电模式中，SDRAM 自动刷新, REFRESH 寄存器[22]bit : 0- auto

refresh; 1 - self refresh

BIT_SELFREFRESH EQU(1<<22)



; 处理器模式常量: CPSR 寄存器的后 5 位决定目前处理器模式 M[4:0]

USERMODE EQU 0x10

FIQMODE EQU 0x11



;定义处理器各模式下堆栈地址常量,_STACK_BASEADDRESS 定义在

option.inc 中

UserStack EQU(_STACK_BASEADDRESS-0x3800);0x33ff4800 ~

SVCStack EQU(_STACK_BASEADDRESS-0x2800);0x33ff5800 ~

UndefStack EQU(_STACK_BASEADDRESS-0x2400);0x33ff5c00 ~

AbortStack EQU(_STACK_BASEADDRESS-0x2000);0x33ff6000 ~

IRQStack EQU(_STACK_BASEADDRESS-0x1000) ;0x33ff7000 ~

FIQStack EQU(_STACK_BASEADDRESS-0x0);0x33ff8000 ~



; 因为存在 ARM 态和 Thumb 态两种工作模式，下一段伪代码用于根据处理器工

作状态确定编译器编译方式

[ {CONFIG} = 16  ; 判断是不是 thumb 状态

THUMBCODE SETL {TRUE}  ; 把 THUMBCODE 设置为 TURE

CODE32  ; 把处理器设置成为 ARM 模式

|

THUMBCODE SETL {FALSE} ; 把 THUMBCODE 设置为 FALSE

 ]







; 下面这段定义了关于在 arm 态和 thumb 态发生跳转时如何保存 LR 的宏,

 movpc,lr ; 目标地址也是 ARM 指令，采用这种方式跳转

]

MEND

MACRO

MOVEQ_PC_LR

[ THUMBCODE ; 同上

 bxeq lr

|

 moveq pc,lr ; 同上

]

MEND

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

; 第二个中断表是 IRQ 中断的子表, 后续会提到

; HANDLER 宏的实现原理如下图:

; H|------| |------|  |------|  |------| |------|

; |/ / / |  |/ / / | |/ / / |  |/ / / |  |/ / / |

; |------|<-sp |------||------|  |------|  |------|<-sp

; |------| |------|<-sp |------| |-isr--|  |------| isr==>pc

; L|------||------| |--r0--|<-sp |--r0--|<-sp |------| r0==>r0

; (0) (1)  (2)  (3)  (4)

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

===============================

ldr r0,[r0] ;读取中断服务程序地址到 r0

str r0,[sp,#4] ;r0 入栈, 中断服务程序地址, 同时 sp-=4, 即保持 sp 不变

ldmfd sp!,{r0,pc} ;出栈, r0 恢复原值, pc 实现跳转

MEND



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

================================

; 2440init.s 采用简单加载方式, 因此这里用 IMPORT 引入变量|Image$$RO$

$Base|等...

; 它们是简单加载方式下由编译器生成的 RO/RW/ZI 段相关参数。

================================

IMPORT |Image$$RO$$Limit| ; End of ROM code (=start of ROM data)

IMPORT |Image$$RW$$Base| ; Base of RAM to initialise

IMPORT |Image$$ZI$$Base| ; Base and limit of area

IMPORT |Image$$ZI$$Limit| ; to zero initialise

;IMPORT OS_CPU_IRQ_ISR ;uCOS_II IrqISR

EXPORT HandleEINT0 ;for os_cpu_a.s



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

================================

; 这里是正真的代码入口，地址 0 代码由此开始

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

================================

EXPORT __ENTRY ; 导出符号_ENTRY，在 ADS 中可作为编译器

参数使用

AREA Init, CODE, READONLY ; 定义名为 Init 的代码段

ENTRY

__ENTRY

ResetEntry

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

ASSERT:DEF:ENDIAN_CHANGE

[ ENDIAN_CHANGE

 ASSERT :DEF:ENTRY_BUS_WIDTH

 [ ENTRY_BUS_WIDTH=32

bChangeBigEndian ;DCD 0xea000007

 ]

 [ ENTRY_BUS_WIDTH=16

andeqr14,r7,r0,lsl #20 ;DCD 0x0007ea00

 ]

 [ ENTRY_BUS_WIDTH=8

streqr0,[r0,-r10,ror #1] ;DCD 0x070000ea

|

 ]

bHandlerUndef ; handler for Undefined mode, 0x04

bHandlerSWI ; handler for SWI interrupt , 0x08

bHandlerPabort ; handler for PAbort , 0x0c

bHandlerDabort ; handler for DAbort , 0x10

b. ; reserved , 0x14

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

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

=============

ChangeBigEndian

[ ENTRY_BUS_WIDTH=32

 DCD0xee110f10;0xee110f10 => mrc p15,0,r0,c1,c0,0

 DCD0xe3800080;0xe3800080 => orr r0,r0,#0x80; //Big-endian

 DCD0xee010f10;0xee010f10 => mcr p15,0,r0,c1,c0,0

]

[ ENTRY_BUS_WIDTH=8

 DCD 0x100f11ee

 DCD 0x800080e3

 DCD 0x100f01ee

 ]

DCD 0xffffffff ;swinv 0xffffff is similar with NOP and run well in both

endian mode.

DCD 0xffffffff

DCD 0xffffffff

DCD 0xffffffff