STM32 keil mdk启动代码发分析 .

学习STM32,看了一堆乱七八糟的文档，准备写程序了，先分析了下STM32的启动代码，看着这堆鬼鬼的汇编代码，挺吓人的，看看帮助，查查网路，还是不那么难懂。

 ;// <h> Stack Configuration
 ;//   <o> Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
 ;// </h>
 Stack_Size      EQU     0x00000200                           ;//定义堆栈大小
                 AREA    STACK, NOINIT, READWRITE, ALIGN=3    ;//定义一个数据段 按8字节对齐
 Stack_Mem       SPACE   Stack_Size                           ;//保留Stack_Size大小的堆栈空间
 __initial_sp                                                 ;//标号，代表堆栈顶部地址，后面有用

 ;// <h> Heap Configuration
 ;//   <o>  Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
 ;// </h>
 Heap_Size       EQU     0x00000020                            ;//定义堆空间大小
                 AREA    HEAP, NOINIT, READWRITE, ALIGN=3      ;//定义一个数据段，8字节对齐
 __heap_base
 Heap_Mem        SPACE   Heap_Size                             ;//保留Heap_Size的堆空间
 __heap_limit                                                  ;//标号，代表堆末尾地址，后面有用

                 PRESERVE8                                     ;//指示编译器8字节对齐
                 THUMB                                         ;//指示编译器为THUMB指令

 ; Vector Table Mapped to Address 0 at Reset
                 AREA    RESET, DATA, READONLY                  ;//定义只读数据段，其实放在CODE区，位于0地址

                 EXTERN  NMIException
                 EXTERN  HardFaultException
                 EXTERN  MemManageException
                 EXTERN  BusFaultException
                 EXTERN  UsageFaultException
                 EXTERN  SVCHandler
                 EXTERN  DebugMonitor
                 EXTERN  PendSVC
                 EXTERN  SysTickHandler                         ;//声明这些符号在外部定义，同C
                                                                ;//在××it.c中实现这些函数 ，中断就能自动调用了
                 EXPORT  __Vectors
 __Vectors       DCD     __initial_sp              ; Top of Stack         //Cotex-M  要求此处为堆栈顶部地址
                 DCD     Reset_Handler             ; Reset Handler
                 DCD     NMIException              ; NMI Handler
                 DCD     HardFaultException        ; Hard Fault Handler
                 DCD     MemManageException        ; MPU Fault Handler
                 DCD     BusFaultException         ; Bus Fault Handler
                 DCD     UsageFaultException       ; Usage Fault Handler
                 DCD     0                         ; Reserved
                 DCD     0                         ; Reserved
                 DCD     0                         ; Reserved
                 DCD     0                         ; Reserved
                 DCD     SVCHandler                ; SVCall Handler
                 DCD     DebugMonitor              ; Debug Monitor Handler
                 DCD     0                         ; Reserved
                 DCD     PendSVC                   ; PendSV Handler
                 DCD     SysTickHandler            ; SysTick Handler      //一大堆的异常处理函数地址
                 ; External Interrupts
                 EXTERN  WWDG_IRQHandler
                 EXTERN  PVD_IRQHandler
                 EXTERN  TAMPER_IRQHandler
                 EXTERN  RTC_IRQHandler
                 EXTERN  FLASH_IRQHandler
                 EXTERN  RCC_IRQHandler
                 EXTERN  EXTI0_IRQHandler
                 EXTERN  EXTI1_IRQHandler
                 EXTERN  EXTI2_IRQHandler
                 EXTERN  EXTI3_IRQHandler
                 EXTERN  EXTI4_IRQHandler
                 EXTERN  DMAChannel1_IRQHandler
                 EXTERN  DMAChannel2_IRQHandler
                 EXTERN  DMAChannel3_IRQHandler
                 EXTERN  DMAChannel4_IRQHandler
                 EXTERN  DMAChannel5_IRQHandler
                 EXTERN  DMAChannel6_IRQHandler
                 EXTERN  DMAChannel7_IRQHandler
                 EXTERN  ADC_IRQHandler
                 EXTERN  USB_HP_CAN_TX_IRQHandler
                 EXTERN  USB_LP_CAN_RX0_IRQHandler
                 EXTERN  CAN_RX1_IRQHandler
                 EXTERN  CAN_SCE_IRQHandler
                 EXTERN  EXTI9_5_IRQHandler
                 EXTERN  TIM1_BRK_IRQHandler
                 EXTERN  TIM1_UP_IRQHandler
                 EXTERN  TIM1_TRG_COM_IRQHandler
                 EXTERN  TIM1_CC_IRQHandler
                 EXTERN  TIM2_IRQHandler
                 EXTERN  TIM3_IRQHandler
                 EXTERN  TIM4_IRQHandler
                 EXTERN  I2C1_EV_IRQHandler
                 EXTERN  I2C1_ER_IRQHandler
                 EXTERN  I2C2_EV_IRQHandler
                 EXTERN  I2C2_ER_IRQHandler
                 EXTERN  SPI1_IRQHandler
                 EXTERN  SPI2_IRQHandler
                 EXTERN  USART1_IRQHandler
                 EXTERN  USART2_IRQHandler
                 EXTERN  USART3_IRQHandler
                 EXTERN  EXTI15_10_IRQHandler
                 EXTERN  RTCAlarm_IRQHandler
                 EXTERN  USBWakeUp_IRQHandler                    ;//同上，

                 DCD     WWDG_IRQHandler           ; Window Watchdog
                 DCD     PVD_IRQHandler            ; PVD through EXTI Line detect
                 DCD     TAMPER_IRQHandler         ; Tamper
                 DCD     RTC_IRQHandler            ; RTC
                 DCD     FLASH_IRQHandler          ; Flash
                 DCD     RCC_IRQHandler            ; RCC
                 DCD     EXTI0_IRQHandler          ; EXTI Line 0
                 DCD     EXTI1_IRQHandler          ; EXTI Line 1
                 DCD     EXTI2_IRQHandler          ; EXTI Line 2
                 DCD     EXTI3_IRQHandler          ; EXTI Line 3
                 DCD     EXTI4_IRQHandler          ; EXTI Line 4
                 DCD     DMAChannel1_IRQHandler    ; DMA Channel 1
                 DCD     DMAChannel2_IRQHandler    ; DMA Channel 2
                 DCD     DMAChannel3_IRQHandler    ; DMA Channel 3
                 DCD     DMAChannel4_IRQHandler    ; DMA Channel 4
                 DCD     DMAChannel5_IRQHandler    ; DMA Channel 5
                 DCD     DMAChannel6_IRQHandler    ; DMA Channel 6
                 DCD     DMAChannel7_IRQHandler    ; DMA Channel 7
                 DCD     ADC_IRQHandler            ; ADC
                 DCD     USB_HP_CAN_TX_IRQHandler  ; USB High Priority or CAN TX
                 DCD     USB_LP_CAN_RX0_IRQHandler ; USB Low  Priority or CAN RX0
                 DCD     CAN_RX1_IRQHandler        ; CAN RX1
                 DCD     CAN_SCE_IRQHandler        ; CAN SCE
                 DCD     EXTI9_5_IRQHandler        ; EXTI Line 9..5
                 DCD     TIM1_BRK_IRQHandler       ; TIM1 Break
                 DCD     TIM1_UP_IRQHandler        ; TIM1 Update
                 DCD     TIM1_TRG_COM_IRQHandler   ; TIM1 Trigger and Commutation
                 DCD     TIM1_CC_IRQHandler        ; TIM1 Capture Compare
                 DCD     TIM2_IRQHandler           ; TIM2
                 DCD     TIM3_IRQHandler           ; TIM3
                 DCD     TIM4_IRQHandler           ; TIM4
                 DCD     I2C1_EV_IRQHandler        ; I2C1 Event
                 DCD     I2C1_ER_IRQHandler        ; I2C1 Error
                 DCD     I2C2_EV_IRQHandler        ; I2C2 Event
                 DCD     I2C2_ER_IRQHandler        ; I2C2 Error
                 DCD     SPI1_IRQHandler           ; SPI1
                 DCD     SPI2_IRQHandler           ; SPI2
                 DCD     USART1_IRQHandler         ; USART1
                 DCD     USART2_IRQHandler         ; USART2
                 DCD     USART3_IRQHandler         ; USART3
                 DCD     EXTI15_10_IRQHandler      ; EXTI Line 15..10
                 DCD     RTCAlarm_IRQHandler       ; RTC Alarm through EXTI Line
                 DCD     USBWakeUp_IRQHandler      ; USB Wakeup from suspend   ;//同上

                 AREA    |.text|, CODE, READONLY        ;//定义代码段

 ; Reset Handler
 Reset_Handler   PROC                                        ;//Rset_Handler的实现
                 EXPORT  Reset_Handler             [WEAK]    ;//在外部没有定义该符号时导出该符号，见HELP中[WEAK]
                 IMPORT  __main                              ;//导入符号,__main为 运行时库提供的函数；完成堆栈，堆的初始话
                 LDR     R0, =__main                         ;//等工作，会调用下面定义的__user_initial_stackheap；
                 BX      R0                                  ;//跳到__main，进入C的世界
                 ENDP

                 ALIGN

 ; User Initial Stack & Heap
                 IF      :DEF:__MICROLIB                     ;//如果使用micro lib,micro lib 描述见armlib.chm

                 EXPORT  __initial_sp
                 EXPORT  __heap_base
                 EXPORT  __heap_limit                        ;//只导出几个定义

                 ELSE                                        ;//如果使用默认C运行时库

                 IMPORT  __use_two_region_memory
                 EXPORT  __user_initial_stackheap
 __user_initial_stackheap                                    ;//则进行堆栈和堆的赋值，在__main函数执行过程中调用。
                 LDR     R0, =  Heap_Mem
                 LDR     R1, =(Stack_Mem + Stack_Size)
                 LDR     R2, = (Heap_Mem +  Heap_Size)
                 LDR     R3, = Stack_Mem
                 BX      LR
                 ALIGN
                 ENDIF

                 END                                         ;//OK ，完了