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标题: bootloader的启动代码（汇编） [打印本页]

作者: m1_ljp 时间: 2013-3-15 14:15 标题: bootloader的启动代码（汇编）

bootloader理论上被分成了stage1(boot code)和stage2(main code)两部分，而boot code部分代码比较难看懂，都是汇编，我也是弄了好些天才搞懂的，真是不易，拿出来大家分享下吧！
我用的是三星的一款开发板，s3c2440，基于arm9的处理器，由于字数限制，一下我只列出了比较难懂的部分。

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

; 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 mode

; 2003.03.14

onGo: Modified for 2440.

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

GET option.inc

GET memcfg.inc ;nand flash config

GET 2440addr.inc;定义内部寄存器地址对应的变量

BIT_SELFREFRESH EQU (1<<22)

re-defined constants

;对arm处理器模式寄存器对应值的常数定义，arm处理器中有一个CPSR程序状态寄存器，它的后五位决定目前处理器模式

USERMODEEQU 0x10

FIQMODEEQU 0x11

IRQMODEEQU 0x12

SVCMODEEQU 0x13

ABORTMODEEQU 0x17

UNDEFMODEEQU 0x1b

MODEMASKEQU 0x1f

NOINTEQU 0xc0

;The location of stacks

;定义各模式下SDRAM中堆栈起始地址，均是物理地址值

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 ~

;Check if tasm.exe(armasm -16 ...@ADS 1.0) is used.

;这一段是为了统一处理器工作状态和软件编译方式（16位编译环境使用tasm.exe编译）

;arm有两种工作状态1.32位，该状态执行字对准的arm指令；2.16位，该状态执行半字对准的Thumb指令

;不同的工作状态，编译器编译方式也不同

GBLLTHUMBCODE

[ {CONFIG} = 16 ;if config

THUMBCODE SETL{TRUE}

CODE32 ;转入32位编译模式

| ;else

THUMBCODE SETL{FALSE} ;设置为FALSE

]

MACRO

MOV_PC_LR

[ THUMBCODE

bx lr

|

mov pc,lr

]

MEND

MACRO

MOVEQ_PC_LR

[ THUMBCODE

bxeq lr

|

moveq pc,lr

]

MEND

;下面这个宏用于把中断服务程序的首地址装载到pc中，加载程序，属于向量中断模式

MACRO ;声明一个宏

$HandlerLabel HANDLER $HandleLabel

$HandlerLabel ;中断服务入口地址

sub sp,sp,#4 ;decrement sp(to store jump address)

;将要使用的r0寄存器入栈

stmfd sp!,{r0}

USH the work register to stack(lr does't push because it return to original address)

;间接寻址方式获得中断函数入口地址

ldrr0,=$HandleLabel;load the address of HandleXXX to r0

ldrr0,[r0] ;load the contents(service routine start address) of HandleXXX

;将对应的中断向量首地址入栈

strr0,[sp,#4];store the contents(ISR) of HandleXXX to stack

;将中断函数首地址出栈，放入程序指针中，系统将跳转到对应中断处理函数

ldmfdsp!,{r0,pc}

OP the work register and pc(jump to ISR)

MEND ;宏结束

;对于arm由RO,RW,ZI三个段组成其中RO为代码段 RW是已经初始化的全局变量 ZI是未初始化的全局变量

;bootloader要将RW段复制到RAM中并将ZI段清零

;编译器使用下列段来记录各段的起始和结束地址

IMPORT|Image$$RO$$Base| ; Base of ROM code

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 MMU_SetAsyncBusMode

IMPORT MMU_SetFastBusMode ;hzh

IMPORTMain; The main entry of mon program引入外部函数

;定义arm汇编程序段，段名Init,程序段为只读代码段

AREAInit,CODE,READONLY

;程序入口

;异常中断向量表（每个表项占4个字节）

;一旦系统运行时有中断发生处理器已经把控制权交给了操作系统处理器还是会跳转到从0x0开始执行中断向量表中某个中断表项

;板子上电和复位后程序开始从位于0x0处开始执行即从这里开始执行跳转到标号为ResetHandler处执行

ENTRY

EXPORT __ENTRY

__ENTRY

ResetEntry

;1)The code, which converts to Big-endian, should be in little endian code.

;2)The following little endian code will be compiled in Big-Endian mode.

;The code byte order should be changed as the memory bus width.

;3)The pseudo instruction,DCD can't be used here because the linker generates error.

;总线宽度判断

;条件编译,在编译成机器码前就设定好

ASSERT

EF:ENDIAN_CHANGE ;判断ENDIAN_CHANGE是否已定义

[ ENDIAN_CHANGE

ASSERT

EF:ENTRY_BUS_WIDTH

[ ENTRY_BUS_WIDTH=32

b ChangeBigEndian;DCD 0xea000007

]

[ ENTRY_BUS_WIDTH=16

andeq r14,r7,r0,lsl #20;DCD 0x0007ea00也是b ChangeBigEndian指令，只是由于总线不一样而取机器码顺序不同罢了

]

[ ENTRY_BUS_WIDTH=8

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

]

|

b ResetHandler

]

;跳转指令，异常中断处理向量

b HandlerUndef ;handler for Undefined mode

b HandlerSWI ;handler for SWI interrupt

b HandlerPabort ;handler for PAbort

b HandlerDabort ;handler for DAbort

b . ;reserved

b HandlerIRQ ;handler for IRQ interrupt

b HandlerFIQ ;handler for FIQ interrupt

;@0x20

b EnterPWDN ; Must be @0x20.

;大小端判断

ChangeBigEndian

;@0x24

[ 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=16

DCD 0x0f10ee11

DCD 0x0080e380

DCD 0x0f10ee01

]

[ 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

DCD 0xffffffff

b ResetHandler

;下面是具体的中断处理函数跳转的宏

;通过上面的$HandlerLabel宏定义展开后跳转到对应的中断处理函数

HandlerFIQHANDLER HandleFIQ

HandlerIRQHANDLER HandleIRQ

HandlerUndefHANDLER HandleUndef

HandlerSWIHANDLER HandleSWI

HandlerDabortHANDLER HandleDabort

HandlerPabortHANDLER HandlePabort

;下面这段程序是用来处理非向量中断

;具体判断I_ISPR中个位是否置1，置1表示等待

;采用INTOFFSET寄存器判定IRQ中断源

IsrIRQ

sub sp,sp,#4;reserved for PC

stmfd sp!,{r8-r9}

ldr r9,=INTOFFSET

ldr r9,[r9] ;载入I_ISR

ldr r8,=HandleEINT0

add r8,r8,r9,lsl #2 ;r8=r8+(r9<<2)

ldr r8,[r8]

str r8,[sp,#8]

ldmfd sp!,{r8-r9,pc}

LTORG

;=======

; ENTRY

;=======

;板子上电和复位后程序开始从位于0x0执行 b ResetHandler程序处跳转到这里执行

ResetHandler

;1.禁止看门狗屏蔽所有中断

ldr r0,=WTCON;watch dog disable

ldr r1,=0x0

str r1,[r0]

ldr r0,=INTMSK

ldr r1,=0xffffffff;all interrupt disable

str r1,[r0]

ldr r0,=INTSUBMSK

ldr r1,=0x7fff ;all sub interrupt disable

str r1,[r0]

;系统启动指示灯显示

[ {FALSE}

; rGPFDAT = (rGPFDAT & ~(0xf<<4)) | ((~data & 0xf)<<4);

; Led_Display

ldr r0,=GPFCON

ldr r1,=0x5500

str r1,[r0]

ldr r0,=GPFDAT

ldr r1,=0x10

str r1,[r0]

]

;2.根据工作频率设置PLL

;mpll=(2*m*Fin)/(p*2~s)m=M_MDIV+8p=M_PDIV+2 s="M"_SDIV

;m=92+8p=1+2s=1mpll=400M

;CLKDIV_VAL = 1:4:8hclk=100Mpclk=50M

;To reduce PLL lock time, adjust the LOCKTIME register.

ldr r0,=LOCKTIME

ldr r1,=0xffffff

str r1,[r0]

[ PLL_ON_START

; Added for confirm clock divide. for 2440.

; Setting value Fclk:Hclk

clk

ldr r0,=CLKDIVN

ldr r1,=CLKDIV_VAL ; 0=1:1:1, 1=1:1:2, 2=1:2:2, 3=1:2:4, 4=1:4:4, 5=1:4:8, 6=1:3:3, 7=1:3:6.

str r1,[r0]

; MMU_SetAsyncBusMode and MMU_SetFastBusMode over 4K, so dont' call here

; call it after copy, hzh

; [ CLKDIV_VAL>1 ; means Fclk:Hclk is not 1:1.

; bl MMU_SetAsyncBusMode

; |

; bl MMU_SetFastBusMode ; default value.

; ]

;program has not been copied, so use these directly, hzh

[ CLKDIV_VAL>1 ; means Fclk:Hclk is not 1:1.

mrc p15,0,r0,c1,c0,0

orr r0,r0,#0xc0000000;R1_nF:OR:R1_iA

mcr p15,0,r0,c1,c0,0

|

mrc p15,0,r0,c1,c0,0

bic r0,r0,#0xc0000000;R1_iA:OR:R1_nF

mcr p15,0,r0,c1,c0,0

]

;Configure UPLL

ldr r0,=UPLLCON

ldr r1,=((U_MDIV<<12)+(U_PDIV<<4)+U_SDIV)

str r1,[r0]

nop ; Caution: After UPLL setting, at least 7-clocks delay must be inserted for setting hardware be completed.

nop

nop

nop

nop

nop

nop

;Configure MPLL

ldr r0,=MPLLCON

ldr r1,=((M_MDIV<<12)+(M_PDIV<<4)+M_SDIV);Fin=16.9344MHz

str r1,[r0]

]

;Check if the boot is caused by the wake-up from SLEEP mode.

ldr r1,=GSTATUS2

ldr r0,[r1]

tst r0,#0x2

;In case of the wake-up from SLEEP mode, go to SLEEP_WAKEUP handler.

bne WAKEUP_SLEEP

EXPORT StartPointAfterSleepWakeUp

StartPointAfterSleepWakeUp

;3.设置存储相关寄存器的程序

;SDRAM,FLASH存储器连接和工作时序的程序，片选定义的程序

;SMRDATA map在下面的程序中定义，另外参考memcfg.s程序

;Set memory control registers

;ldr r0,=SMRDATA

adrl r0, SMRDATA ;be careful!, hzh

ldr r1,=BWSCON ;BWSCON Address

add r2, r0, #52 ;End address of SMRDATA

0

ldr r3, [r0], #4

str r3, [r1], #4

cmp r2, r0

bne %B0

;===delay, hzh

mov r0, #&1000

1

subs r0, r0, #1

bne %B1

;===

;5.设置缺省中断处理函数

; Setup IRQ handler

ldr r0,=HandleIRQ;This routine is needed

ldr r1,=IsrIRQ;if there isn't 'subs pc,lr,#4' at 0x18, 0x1c

str r1,[r0]

; ;Copy and paste RW data/zero initialized data

; ldr r0, =|Image$$RO$$Limit| ; Get pointer to ROM data

; ldr r1, =|Image$$RW$$Base|; and RAM copy

; ldr r3, =|Image$$ZI$$Base|

;

;6.将数据段拷贝到RAM中将零初始化数据段清零跳入C语言的main函数执行

;到这步结束bootloader 的stage1引导

; ;Zero init base => top of initialised data

; cmp r0, r1; Check that they are different

; beq %F2

;1

; cmp r1, r3; Copy init data

; ldrcc r2, [r0], #4;--> LDRCC r2, [r0] + ADD r0, r0, #4

; strcc r2, [r1], #4;--> STRCC r2, [r1] + ADD r1, r1, #4

; bcc %B1

;2

; ldr r1, =|Image$$ZI$$Limit| ; Top of zero init segment

; mov r2, #0

;3

; cmp r3, r1; Zero init

; strcc r2, [r3], #4

; bcc %B3

[

NOT:THUMBCODE

bl Main ;Don't use main() because ......

;ldr pc, =Main ;hzh

b .

]

[ THUMBCODE ;for start-up code for Thumb mode

orr lr,pc,#1

bx lr

CODE16

bl Main ;Don't use main() because ......

b .

CODE32

]

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

LTORG ;声明一个数据缓冲池的开始

;GCS0->SST39VF1601

;GCS1->16c550

;GCS2->IDE

;GCS3->CS8900

;GCS4->DM9000

;GCS5->CF Card

;GCS6->SDRAM

;GCS7->unused

;这是上面提到的对存储器初始化的数据map

SMRDATA DATA

; Memory configuration should be optimized for best performance

; The following parameter is not optimized.

; Memory access cycle parameter strategy

; 1) The memory settings issafe parameters even at HCLK="75Mhz".

; 2) SDRAM refresh period is for HCLK<=75Mhz.

DCD (0+(B1_BWSCON<<4)+(B2_BWSCON<<8)+(B3_BWSCON<<12)+(B4_BWSCON<<16)+(B5_BWSCON<<20)+(B6_BWSCON<<24)+(B7_BWSCON<<28))

DCD ((B0_Tacs<<13)+(B0_Tcos<<11)+(B0_Tacc<<8)+(B0_Tcoh<<6)+(B0_Tah<<4)+(B0_Tacp<<2)+(B0_PMC));GCS0

DCD ((B1_Tacs<<13)+(B1_Tcos<<11)+(B1_Tacc<<8)+(B1_Tcoh<<6)+(B1_Tah<<4)+(B1_Tacp<<2)+(B1_PMC));GCS1

DCD ((B2_Tacs<<13)+(B2_Tcos<<11)+(B2_Tacc<<8)+(B2_Tcoh<<6)+(B2_Tah<<4)+(B2_Tacp<<2)+(B2_PMC));GCS2

DCD ((B3_Tacs<<13)+(B3_Tcos<<11)+(B3_Tacc<<8)+(B3_Tcoh<<6)+(B3_Tah<<4)+(B3_Tacp<<2)+(B3_PMC));GCS3

DCD ((B4_Tacs<<13)+(B4_Tcos<<11)+(B4_Tacc<<8)+(B4_Tcoh<<6)+(B4_Tah<<4)+(B4_Tacp<<2)+(B4_PMC));GCS4

DCD ((B5_Tacs<<13)+(B5_Tcos<<11)+(B5_Tacc<<8)+(B5_Tcoh<<6)+(B5_Tah<<4)+(B5_Tacp<<2)+(B5_PMC));GCS5

DCD ((B6_MT<<15)+(B6_Trcd<<2)+(B6_SCAN));GCS6

DCD ((B7_MT<<15)+(B7_Trcd<<2)+(B7_SCAN));GCS7

DCD ((REFEN<<23)+(TREFMD<<22)+(Trp<<20)+(Tsrc<<18)+(Tchr<<16)+REFCNT)

DCD 0x32;SCLK power saving mode, BANKSIZE 128M/128M

;DCD 0x02;SCLK power saving disable, BANKSIZE 128M/128M

DCD 0x30;MRSR6 CL="3clk"

DCD 0x30;MRSR7 CL="3clk"

BaseOfROM DCD |Image$$RO$$Base|

TopOfROM DCD |Image$$RO$$Limit|

BaseOfBSS DCD |Image$$RW$$Base|

BaseOfZero DCD |Image$$ZI$$Base|

EndOfBSS DCD |Image$$ZI$$Limit|

ALIGN ;通过添加补丁字节使当前位置满足一定的对齐方式

;Function for entering power down mode

; 1. SDRAM should be in self-refresh mode.

; 2. All interrupt should be maksked for SDRAM/DRAM self-refresh.

; 3. LCD controller should be disabled for SDRAM/DRAM self-refresh.

; 4. The I-cache may have to be turned on.

; 5. The location of the following code may have not to be changed.

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