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bootloader的启动代码（汇编）

已有 112 次阅读  2013-03-15 14:14

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:DonGo: 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)


;Pre-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} ;PUSH 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};POP 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 :DEF:ENDIAN_CHANGE ;判断ENDIAN_CHANGE是否已定义

[ 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:Pclk

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



[ :LNOT: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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