STM32 keil mdk启动代码发分析
在启动文件我们看到了__main和用户写的main，这2个是有区别的，大概流程如下：
1、复位第一条指令：Reset_Handler PROC，这里指定为 LDR R0, =__main。表示调用库函数__main，当然，我们可以在__main前做点事情，比如PLL初始化等。
2、__main()的执行流程参考：
http://www.rritw.com/a/bianchengyuyan/_NET/20120611/128129.html
跟一下汇编，大概是__scatterload()->__rt_entry()->__user_setup_stackheap()
3、最后调用用户的main()函数。
4、可以不使用C库初始化函数__main()直接调用用户的main()【或别的定义！】，这个可以google一下。
;// <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
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