ARM啟動(dòng)過(guò)程(Cortex-M3 NXP LPC1768為例)

; Stack Configuration

; Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>

;

Stack_Size EQU 0x00000200

AREA STACK, NOINIT, READWRITE, ALIGN=3

//指明8字節(jié)對(duì)齊（ALIGN=3）

Stack_Mem SPACE Stack_Size

__initial_sp //此標(biāo)號(hào)有一層隱含的意思那就是在M3中堆棧是滿遞減堆 //棧，因?yàn)樗付?strong>堆棧指針位于堆棧的高地址（在 //Stack_Mem之后）

; Heap Configuration

; Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>

;

Heap_Size EQU 0x00000000

AREA HEAP, NOINIT, READWRITE, ALIGN=3

__heap_base

Heap_Mem SPACE Heap_Size

__heap_limit

PRESERVE8

//PRESERVE8指定了以下的代碼位8字節(jié)對(duì)齊

THUMB

; Vector Table Mapped to Address 0 at Reset

AREA RESET, DATA, READONLY

//此語(yǔ)句聲明RESET數(shù)據(jù)段

EXPORT __Vectors

//導(dǎo)出向量表標(biāo)號(hào)，EXPORT作用類似于C語(yǔ)言中的extern

__Vectors

DCD __initial_sp ; Top of Stack

DCD Reset_Handler ; Reset Handler

DCD NMI_Handler ; NMI Handler

DCD HardFault_Handler ; Hard Fault Handler

DCD MemManage_Handler ; MPU Fault Handler

DCD BusFault_Handler ; Bus Fault Handler

DCD UsageFault_Handler ; Usage Fault Handler

DCD 0 ; Reserved

DCD 0 ; Reserved

DCD 0 ; Reserved

DCD 0 ; Reserved

DCD SVC_Handler ; SVCall Handler

DCD DebugMon_Handler ; Debug Monitor Handler

DCD 0 ; Reserved

DCD PendSV_Handler ; PendSV Handler

DCD SysTick_Handler ; SysTick Handler

; External Interrupts

DCD WDT_IRQHandler ; 16: Watchdog Timer

DCD TIMER0_IRQHandler ; 17: Timer0

DCD TIMER1_IRQHandler ; 18: Timer1

DCD TIMER2_IRQHandler ; 19: Timer2

DCD TIMER3_IRQHandler ; 20: Timer3

DCD UART0_IRQHandler ; 21: UART0

（……省略）

; Reset Handler

Reset_Handler

PROC

EXPORT Reset_Handler [WEAK]

IMPORT SystemInit

IMPORT __main

LDR R0, =SystemInit

BLX R0

LDR R0, =__main

BX R0

ENDP

這段代碼是NXP公司的LPC1700系列的MCU特有的一段代碼，其他公司的Cortex-M3 MCU的啟動(dòng)程序是沒有這段代碼的。

這段代碼是指定LPC1700的CRP加密級(jí)別的代碼段，芯片上電后會(huì)自動(dòng)讀取這一地址的值以確定加密方式，其中CRP_Key = 0xffffffff為不加密（0級(jí)加密），CRP_Key = 0x12345678為1級(jí)加密，CRP_Key = 0x87654321為2級(jí)加密，CRP_Key = 0x43218765為3級(jí)加密（最高級(jí)加密），3級(jí)加密將會(huì)禁止所有的ISP指令，也就是說(shuō)，芯片將不能讀寫、不能擦除。

IF :LNOT::DEF:NO_CRP

AREA |.ARM.__at_0x02FC|, CODE, READONLY

CRP_Key

DCD 0xFFFFFFFF

ENDIF

AREA |.text|, CODE, READONLY

; User Initial Stack & Heap

IF :DEF:__MICROLIB

EXPORT __initial_sp

EXPORT __heap_base

EXPORT __heap_limit

ELSE

IMPORT __use_two_region_memory

EXPORT __user_initial_stackheap

__user_initial_stackheap

LDR R0, = Heap_Mem

LDR R1, = (Stack_Mem + Stack_Size)

LDR R2, = (Heap_Mem + Heap_Size)

LDR R3, = Stack_Mem

BX LR