启动代码文件名是STM32F10X.S，它的作用先总结下，然后再分析。启动代码作用一般是：1）堆和栈的初始化；2）向量表定义；3）地址重映射及中断向量表的转移；4）设置系统时钟频率；5）中断寄存器的初始化；6）进入C应用程序。
（1）按启动代码的次序，先看堆和栈的初始化：
Stack_Size EQU 0x00000200 ；定义Stack_Size为0x00000200
AREA STACK, NOINIT, READWRITE, ALIGN=3 ；定义栈，可初始为0，8字节对齐
Stack_Mem SPACE Stack_Size ；分配0x200个连续字节，并初始化为0
__initial_sp ；汇编代码地址标号
Heap_Size EQU 0x00000000
AREA HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem SPACE Heap_Size
__heap_limit
PRESERVE8 ；指定当前文件堆栈8字节对齐
THUMB ；告诉汇编器下面是32为的Thumb指令，如果需要汇编器将插入位以保证对齐
（2）中断向量表定义
AREA RESET, DATA, READONLY ;定义复位向量段，只读
EXPORT __Vectors ；定义一个可以在其他文件中使用的全局标号。此处表示中断地址
__Vectors DCD __initial_sp ; 给__initial_sp分配4字节32位的地址0x0
DCD Reset_Handler ; 给标号Reset Handler分配地址为0x00000004
DCD NMI_Handler ; 给标号NMI Handler分配地址0x00000008
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 ; 这种形式就是保留地址，不给任何标号分配
Handler
DCD 0 DCD 0 DCD 0 DCD SVC_Handler DCD DebugMon_Handler DCD 0 DCD PendSV_Handler DCD SysTick_Handler ; External Interrupts
; Reserved
; Reserved
; Reserved
; SVCall Handler
; Debug Monitor ; Reserved
; PendSV Handler
; SysTick Handler
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
CAN TX
CAN RX0
DMAChannel6_IRQHandler ; DMA Channel 6
DMAChannel7_IRQHandler ; DMA Channel 7
ADC_IRQHandler ; ADC
USB_HP_CAN_TX_IRQHandler ; USB High Priority or USB_LP_CAN_RX0_IRQHandler ; USB Low Priority or CAN_RX1_IRQHandler ; CAN RX1
CAN_SCE_IRQHandler ; CAN SCE
EXTI9_5_IRQHandler ; EXTI Line 9..5
TIM1_BRK_IRQHandler ; TIM1 Break
DCD DCD DCD DCD DCD DCD DCD DCD DCD 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 DCD TIM3_IRQHandler DCD TIM4_IRQHandler DCD I2C1_EV_IRQHandler DCD I2C1_ER_IRQHandler DCD I2C2_EV_IRQHandler DCD I2C2_ER_IRQHandler DCD SPI1_IRQHandler DCD SPI2_IRQHandler DCD USART1_IRQHandler ; TIM2
; TIM3
; TIM4
; I2C1 Event
; I2C1 Error
; I2C2 Event
; I2C2 Error
; SPI1
; SPI2
; 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
（3）中断向量表的转移
AREA |.text|, CODE, READONLY ；代码段定义
; Reset Handler
Reset_Handler PROC ；标记一个函数的开始
EXPORT Reset_Handler [WEAK]；[WEAK] 选项表示当所有的源文件都没有 定义这样一个标号时，编译器也不给出错误信息，在多数情况下将该标号置为 0 ，若该标号为 B 或 BL 指令引用，则将 B 或 BL指令置为 NOP 操作。EXPORT提示编译器该标号可以为外部文件引用。
IMPORT __main ;通知编译器要使用的标号在其他文件
LDR R0, =__main；使用“=”表示LDR目前是伪指令不是标准指令。这里是把__main的地址给RO。
BX R0；BX是ARM指令集和THUMB指令集之间程序的跳转
ENDP
; Dummy Exception Handlers (infinite loops which can be modified)
NMI_Handler m ;\"m\"其实就是PROC表示汇编函数的开始
EXPORT NMI_Handler [WEAK]
B .
ENDP
HardFault_Handler\\ ;\"\\\"是换行的意思
PROC
EXPORT HardFault_Handler [WEAK]
B . ;\".\"号到底是什么含义呢，目前还没查到资料。可能是保留地址，供以后修改的吧
ENDP
MemManage_Handler\\
PROC
EXPORT MemManage_Handler B .
ENDP
BusFault_Handler\\
PROC
EXPORT BusFault_Handler B .
ENDP
UsageFault_Handler\\
PROC
[WEAK]
[WEAK]
EXPORT UsageFault_Handler [WEAK]
B .
ENDP
SVC_Handler PROC
EXPORT SVC_Handler B .
ENDP
DebugMon_Handler\\
PROC
EXPORT DebugMon_Handler B .
ENDP
PendSV_Handler PROC
[WEAK]
[WEAK]
EXPORT PendSV_Handler [WEAK]
B .
ENDP
SysTick_Handler PROC
EXPORT SysTick_Handler B .
ENDP
Default_Handler PROC
EXPORT WWDG_IRQHandler EXPORT PVD_IRQHandler EXPORT TAMPER_IRQHandler EXPORT RTC_IRQHandler EXPORT FLASH_IRQHandler [WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
EXPORT RCC_IRQHandler [WEAK]
EXPORT EXTI0_IRQHandler [WEAK]
EXPORT EXTI1_IRQHandler [WEAK]
EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT [WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
EXTI2_IRQHandler [WEAK]
EXTI3_IRQHandler [WEAK]
EXTI4_IRQHandler [WEAK]
DMAChannel1_IRQHandler DMAChannel2_IRQHandler DMAChannel3_IRQHandler DMAChannel4_IRQHandler DMAChannel5_IRQHandler DMAChannel6_IRQHandler DMAChannel7_IRQHandler EXPORT ADC_IRQHandler [WEAK]
EXPORT USB_HP_CAN_TX_IRQHandler [WEAK]
EXPORT USB_LP_CAN_RX0_IRQHandler [WEAK]
EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT CAN_RX1_IRQHandler [WEAK]
CAN_SCE_IRQHandler [WEAK]
EXTI9_5_IRQHandler [WEAK]
TIM1_BRK_IRQHandler [WEAK]
TIM1_UP_IRQHandler [WEAK]
TIM1_TRG_COM_IRQHandler [WEAK]
TIM1_CC_IRQHandler [WEAK]
TIM2_IRQHandler [WEAK]
TIM3_IRQHandler [WEAK]
TIM4_IRQHandler [WEAK]
EXPORT I2C1_EV_IRQHandler [WEAK]
EXPORT I2C1_ER_IRQHandler [WEAK]
EXPORT I2C2_EV_IRQHandler [WEAK]
EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT EXPORT WWDG_IRQHandler
I2C2_ER_IRQHandler SPI1_IRQHandler SPI2_IRQHandler USART1_IRQHandler USART2_IRQHandler USART3_IRQHandler EXTI15_10_IRQHandler RTCAlarm_IRQHandler USBWakeUp_IRQHandler [WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
[WEAK]
PVD_IRQHandler
TAMPER_IRQHandler
RTC_IRQHandler
FLASH_IRQHandler
RCC_IRQHandler
EXTI0_IRQHandler
EXTI1_IRQHandler
EXTI2_IRQHandler
EXTI3_IRQHandler
EXTI4_IRQHandler
DMAChannel1_IRQHandler
DMAChannel2_IRQHandler
DMAChannel3_IRQHandler
DMAChannel4_IRQHandler
DMAChannel5_IRQHandler
DMAChannel6_IRQHandler
DMAChannel7_IRQHandler
ADC_IRQHandler
USB_HP_CAN_TX_IRQHandler
USB_LP_CAN_RX0_IRQHandler
CAN_RX1_IRQHandler
CAN_SCE_IRQHandler
EXTI9_5_IRQHandler
TIM1_BRK_IRQHandler
TIM1_UP_IRQHandler
TIM1_TRG_COM_IRQHandler
TIM1_CC_IRQHandler
TIM2_IRQHandler
TIM3_IRQHandler
TIM4_IRQHandler
I2C1_EV_IRQHandler
I2C1_ER_IRQHandler
I2C2_EV_IRQHandler
I2C2_ER_IRQHandler
SPI1_IRQHandler
SPI2_IRQHandler
USART1_IRQHandler
USART2_IRQHandler
USART3_IRQHandler
EXTI15_10_IRQHandler
RTCAlarm_IRQHandler
USBWakeUp_IRQHandler
B .
ENDP
ALIGN
（4）堆和栈的初始化
IF :DEF:__MICROLIB ；“DEF”的用法——:DEF:X 就是说X定义了则为真，否则为假
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
ALIGN ；填充字节使地址对齐
ENDIF
END
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