启动程序过程：
1、系统硬件初始化
系统上电或复位后，程序从位于地址0x0的Reset Exception Vector处开始执行，因此需要在这里放置Bootloader的第一条指令:b ResetHandler，跳转到标号为ResetHandler处执行第一阶段的硬件初始化，主要内容为：关看门狗，关中断，初始化PLL和时钟，初始化存储器系统。执行完以上程序后，系统进行堆栈和存储器的初始化。系统堆栈初始化取决于用户使用了那些中断，以及系统需要处理那些错误类型。一般情况下，管理者堆栈必须设置，如果使用了IRQ中断，则IRQ堆栈也必须设置。如果系统使用了外设，则需要设置相关的寄存器，以确定其刷新频率、总线宽度等信息。
2、代码段复制到RAM中运行
因为嵌入式系统的代码通常都是固化在ROM或者Flash中，上电后开始运行。由于ROM和Flash的读取速度相对较慢，这样无疑会降低代码的执行速度和系统的运行效率。为此，需要把系统的代码复制到RAM中运行。使用SDT连接器ARMLink产生的定位信息，把RO的有效代码和数据段复制到RAM中。ARMLink将编译后的程序连接成ELF文件。映像文件爱女内部共有三种输出段：RO段，RW段和ZI段。这三种输出段分别包含了制度代码既包含了在代码段中的少量数据、可读写的数据、初始化为0的数据，ARMLink同时还产生了这三种输出段的起始和终止定位信息：Image$$RO$$Base、Image$$RO$$Limit、Image$$RW$$Base、Image$$RW$$Limit、Image$$ZI$$Linit和Image$$ZI$$Limit。可以在程序中使用这些定位信息。将ROM中的代码和数据搬移到RAM中。
3、建立二级中断向量表
在ARM系统中，中断向量表位于0x0开始的地址处，意味着无论运行什么样的上层软件，一旦发生中断，程序就得到Flash存储器中的中断向量表里去，降低系统的运行效率。因此在RAM中建立自己的二级中断向量表，当中断发生后，程序直接从RAM中去中断向量进入中断子程序。尤其是在中断频繁发生的系统里，这种方法可以大大提高系统的运行效率。
4、MMU的应用
MMU是存储器管理单元的缩写，是用来管理虚拟内存系统的器件。MMU通常是CPU的一部分，本身有少量存储空间存放从虚拟地址到物理地址的匹配表，此表称作TLB(转换旁置缓冲区)。所有数据请求都送往MMU，由MMU决定数据是在RAM内还是在大容量外部存储器设备内。如果数据不在存储空间内，MMU将产生页面错误中断。MMU存储器系统的结构允许对存储器系统的精细控制，大部分的控制细节由存在存储器中的转换表提供。这些表的入口定义了从1KB~1MB的各种存储器区域的属性。MMU完成的两个主要功能是：将虚拟地址换成物理地址，控制存储器存取允许。MMU关掉时，虚地址直接输出到物理地址总线。
启动代码完成的主要功能：
1、建立异常中断的入口向量
2、建立中断向量表
3、为ARM每种运行模式设置堆栈
4、初始化ARM的MPLL时钟
5、初始化MMU(内存管理单元)
6、初始化存储器控制器
7、关闭看门狗、关闭中断
8、判断IRQ中断的中断入口
9、将RW段的内容从Flash拷贝到SDRAM，初始化ZI段为0
10、跳转到应用程序（C代码）
***************************启动源码***************************
;=========================================
; NAME: 2410INIT.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,POWER_OFF mode
;=========================================
GET option.inc
GET memcfg.inc
GET 2410addr.inc
BIT_SELFREFRESH EQU (1<<22)
;Pre-defined constants
USERMODE EQU 0x10
FIQMODE EQU 0x11
IRQMODE EQU 0x12
SVCMODE EQU 0x13
ABORTMODE EQU 0x17
UNDEFMODE EQU 0x1b
MODEMASK EQU 0x1f
NOINT EQU 0xc0
;The location of stacks
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 1.0) is used.
GBLL THUMBCODE
[ {CONFIG} = 16
THUMBCODE SETL {TRUE}
CODE32
|
THUMBCODE SETL {FALSE}
]
MACRO
MOV_PC_LR
[ THUMBCODE
bx lr
|
mov pc,lr
]
MEND
MACRO
MOVEQ_PC_LR
[ THUMBCODE
bxeq lr
|
moveq pc,lr
]
MEND
MACRO
$HandlerLabel HANDLER $HandleLabel
$HandlerLabel
sub sp,sp,#4 ;decrement sp(to store jump address)
stmfd sp!,{r0} ;PUSH the work register to stack(lr does't push because it return to original address)
ldr r0,=$HandleLabel;load the address of HandleXXX to r0
ldr r0,[r0] ;load the contents(service routine start address) of HandleXXX
str r0,[sp,#4] ;store the contents(ISR) of HandleXXX to stack
ldmfd sp!,{r0,pc} ;POP the work register and pc(jump to ISR)
MEND
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
AREA SelfBoot, CODE, READONLY
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.
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 ResetHandler
]
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
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
;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.
;void EnterPWDN(int CLKCON);
EnterPWDN
mov r2,r0 ;r2=rCLKCON
tst r0,#0x8 ;POWER_OFF mode?
bne ENTER_POWER_OFF
ENTER_STOP
ldr r0,=REFRESH
ldr r3,[r0] ;r3=rREFRESH
mov r1, r3
orr r1, r1, #BIT_SELFREFRESH
str r1, [r0] ;Enable SDRAM self-refresh
mov r1,#16 ;wait until self-refresh is issued. may not be needed.
0 subs r1,r1,#1
bne %B0
ldr r0,=CLKCON ;enter STOP mode.
str r2,[r0]
mov r1,#32
0 subs r1,r1,#1 ;1) wait until the STOP mode is in effect.
bne %B0 ;2) Or wait here until the CPU&Peripherals will be turned-off
; Entering POWER_OFF mode, only the reset by wake-up is available.
ldr r0,=REFRESH ;exit from SDRAM self refresh mode.
str r3,[r0]
MOV_PC_LR
ENTER_POWER_OFF
;NOTE.
;1) rGSTATUS3 should have the return address after wake-up from POWER_OFF mode.
ldr r0,=REFRESH
ldr r1,[r0] ;r1=rREFRESH
orr r1, r1, #BIT_SELFREFRESH
str r1, [r0] ;Enable SDRAM self-refresh
mov r1,#16 ;Wait until self-refresh is issued,which may not be needed.
0 subs r1,r1,#1
bne %B0
ldr r1,=MISCCR
ldr r0,[r1]
orr r0,r0,#(7<<17) ;Make sure that SCLK0:SCLK->0, SCLK1:SCLK->0, SCKE=L during boot-up
str r0,[r1]
ldr r0,=CLKCON
str r2,[r0]
b . ;CPU will die here.
WAKEUP_POWER_OFF
;Release SCLKn after wake-up from the POWER_OFF mode.
ldr r1,=MISCCR
ldr r0,[r1]
bic r0,r0,#(7<<17) ;SCLK0:0->SCLK, SCLK1:0->SCLK, SCKE:L->H
str r0,[r1]
;Set memory control registers
ldr r0,=SMRDATA
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
mov r1,#256
0 subs r1,r1,#1 ;1) wait until the SelfRefresh is released.
bne %B0
ldr r1,=GSTATUS3 ;GSTATUS3 has the start address just after POWER_OFF wake-up
ldr r0,[r1]
mov pc,r0
LTORG
HandlerFIQ HANDLER HandleFIQ
HandlerIRQ HANDLER HandleIRQ
HandlerUndef HANDLER HandleUndef
HandlerSWI HANDLER HandleSWI
HandlerDabort HANDLER HandleDabort
HandlerPabort HANDLER HandlePabort
IsrIRQ
sub sp,sp,#4 ;reserved for PC
stmfd sp!,{r8-r9}
ldr r9,=INTOFFSET
ldr r9,[r9]
ldr r8,=HandleEINT0
add r8,r8,r9,lsl #2
ldr r8,[r8]
str r8,[sp,#8]
ldmfd sp!,{r8-r9,pc}
;======================================================
; ENTRY
;======================================================
ResetHandler
ldr r0,=WTCON ;watch dog disable
ldr r1,=0x0
str r1,[r0]
;1 ldr r0, =0x300
; ldr r1, [r0]
; b %B1
ldr r0,=INTMSK
ldr r1,=0xffffffff ;all interrupt disable
str r1,[r0]
ldr r0,=INTSUBMSK
ldr r1,=0x3ff ;all sub interrupt disable
str r1,[r0]
[ {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]
]
;To reduce PLL lock time, adjust the LOCKTIME register.
ldr r0,=LOCKTIME
ldr r1,=0xffffff
str r1,[r0]
[ PLL_ON_START
;Configure MPLL
ldr r0,=MPLLCON
ldr r1,=((M_MDIV<<12)+(M_PDIV<<4)+M_SDIV) ;Fin=12MHz,Fout=50MHz
str r1,[r0]
]
;Check if the boot is caused by the wake-up from POWER_OFF mode.
ldr r1,=GSTATUS2
ldr r0,[r1]
tst r0,#0x2
;In case of the wake-up from POWER_OFF mode, go to POWER_OFF_WAKEUP handler.
nop;bne WAKEUP_POWER_OFF
EXPORT StartPointAfterPowerOffWakeUp
StartPointAfterPowerOffWakeUp
;Set memory control registers
adr r0, SMRDATA
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
;禁止Icache和Dcache，禁止MMU
;IMPORT MMU_DisableICache
;bl MMU_DisableICache ;
;IMPORT MMU_DisableDCache
;bl MMU_DisableDCache ;
;IMPORT MMU_InvalidateICache
;bl MMU_InvalidateICache ;
;IMPORT MMU_DisableMMU
;bl MMU_DisableMMU ;
;Initialize stacks
bl InitStacks
; 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]
;===========================================================
adr r0, ResetEntry
ldr r2, BaseOfROM
cmp r0, r2
ldreq r0, TopOfROM
beq InitRam
ldr r3, TopOfROM
0
ldmia r0!, {r4-r7}
stmia r2!, {r4-r7}
cmp r2, r3
bcc %B0
sub r2, r2, r3
sub r0, r0, r2
InitRam
ldr r2, BaseOfBSS
ldr r3, BaseOfZero
0
cmp r2, r3
ldrcc r1, [r0], #4
strcc r1, [r2], #4
bcc %B0
mov r0, #0
ldr r3, EndOfBSS
1
cmp r2, r3
strcc r0, [r2], #4
bcc %B1
[ :LNOT:THUMBCODE
ldr pc, GotoMain ;bl Main ;Don't use main() because ......
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
]
;function initializing stacks
InitStacks
;Don't use DRAM,such as stmfd,ldmfd......
;SVCstack is initialized before
;Under toolkit ver 2.5, 'msr cpsr,r1' can be used instead of 'msr cpsr_cxsf,r1'
mrs r0,cpsr
bic r0,r0,#MODEMASK
orr r1,r0,#UNDEFMODE|NOINT
msr cpsr_cxsf,r1 ;UndefMode
ldr sp,=UndefStack
orr r1,r0,#ABORTMODE|NOINT
msr cpsr_cxsf,r1 ;AbortMode
ldr sp,=AbortStack
orr r1,r0,#IRQMODE|NOINT
msr cpsr_cxsf,r1 ;IRQMode
ldr sp,=IRQStack
orr r1,r0,#FIQMODE|NOINT
msr cpsr_cxsf,r1 ;FIQMode
ldr sp,=FIQStack
bic r0,r0,#MODEMASK|NOINT
orr r1,r0,#SVCMODE
msr cpsr_cxsf,r1 ;SVCMode
ldr sp,=SVCStack
;USER mode has not be initialized.
mov pc,lr
;The LR register won't be valid if the current mode is not SVC mode.
LTORG
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 is safe 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 0x1f7c;((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)+(Trc<<18)+(Tchr<<16)+REFCNT)
DCD 0x32 ;SCLK power saving mode, BANKSIZE 128M/128M
DCD 0x30 ;MRSR6 CL=3clk
DCD 0x30 ;MRSR7
; DCD 0x20 ;MRSR6 CL=2clk
; DCD 0x20 ;MRSR7
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|
GBLS main_entry
main_entry SETS "Main"
IMPORT $main_entry
GotoMain DCD $main_entry
ALIGN
AREA RamData, DATA, READWRITE
^ _ISR_STARTADDRESS
HandleReset # 4
HandleUndef # 4
HandleSWI # 4
HandlePabort # 4
HandleDabort # 4
HandleReserved # 4
HandleIRQ # 4
HandleFIQ # 4
;Don't use the label 'IntVectorTable',
;The value of IntVectorTable is different with the address you think it may be.
;IntVectorTable
HandleEINT0 # 4
HandleEINT1 # 4
HandleEINT2 # 4
HandleEINT3 # 4
HandleEINT4_7 # 4
HandleEINT8_23 # 4
HandleRSV6 # 4
HandleBATFLT # 4
HandleTICK # 4
HandleWDT # 4
HandleTIMER0 # 4
HandleTIMER1 # 4
HandleTIMER2 # 4
HandleTIMER3 # 4
HandleTIMER4 # 4
HandleUART2 # 4
HandleLCD # 4
HandleDMA0 # 4
HandleDMA1 # 4
HandleDMA2 # 4
HandleDMA3 # 4
HandleMMC # 4
HandleSPI0 # 4
HandleUART1 # 4
HandleRSV24 # 4
HandleUSBD # 4
HandleUSBH # 4
HandleIIC # 4
HandleUART0 # 4
HandleSPI1 # 4
HandleRTC # 4
HandleADC # 4
END
