启动文件使用汇编写的，看懂启动文件，需要先了解一些启动文件中用到的汇编指令，这里使用keil编译，启动文件参考startup_stm32f10x_hd.s。
前置知识：相关的汇编指令：
汇编器指令：
EQU:
类似于c中的#define 定义常量。
12.27 EQU
The EQU directive gives a symbolic name to a numeric constant, a register-relative value or a PC-relative value.
Syntax
name EQU expr{, type}
Usage
Use EQU to define constants. This is similar to the use of #define to define a constant in C.
* is a synonym for EQU.
Examples
abc EQU 2 ; Assigns the value 2 to the symbol abc.
xyz EQU label+8 ; Assigns the address (label+8) to the
; symbol xyz.
fiq EQU 0x1C, CODE32 ; Assigns the absolute address 0x1C to
; the symbol fiq, and marks it as code.
AREA:
通知汇编器构造一个代码段或者数据段。
12.6 AREA
The AREA directive instructs the assembler to assemble a new code or data section.
SPACE:
表示一块内存。
12.64 SPACE or FILL
The SPACE directive reserves a zeroed block of memory. The FILL directive reserves a block of memory to fill with a given value.
Usage
Use the ALIGN directive to align any code following a SPACE or FILL directive.
% is a synonym for SPACE.
Example
AREA MyData, DATA, READWRITE
data1 SPACE 255 ; defines 255 bytes of zeroed store
data2 FILL 50,0xAB,1 ; defines 50 bytes containing 0xAB
DCD:
按字（word）申请内存，并初始化。例如：
data1 DCD 1,5,20 ; Defines 3 words containing
; decimal values 1, 5, and 20
data2 DCD mem06 + 4 ; Defines 1 word containing 4 +
; the address of the label mem06
AREA MyData, DATA, READWRITE
DCB 255 ; Now misaligned ...
data3 DCDU 1,5,20 ; Defines 3 words containing
; 1, 5 and 20, not word aligned
启动文件
- 配置栈（Stack）：
; Amount of memory (in bytes) allocated for Stack
; Tailor this value to your application needs
; Stack Configuration
; Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
;
-
EQU类似于#define ,这里就相当于#define Stack_Size 0x1000
Stack_Size EQU 0x00001000 ;
2.AREA构建一个数据段，name=STACK, NOINIT表示不初始化，ALIGN=3表示8字节对齐.
3.表示Stack_Size大小的内存（前面有定义Stack_Size=0x1000）.
4.__initial_sp紧跟Stack_Mem内存块，表示栈顶（这里栈增长方向：高地址->低地址）.
AREA STACK, NOINIT, READWRITE, ALIGN=3 ;
Stack_Mem SPACE Stack_Size ;
__initial_sp ;
- 配置堆（Heap）：
和配置栈方法一样，__heap_base__heap_limit分别是Heap的起始地址。
; Heap Configuration
; Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
;
Heap_Size EQU 0x00000200
AREA HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem SPACE Heap_Size
__heap_limit
- 中断向量表
EXPORT: 使符号具有全局属性。
__Vectors相当于一个数组，元素都是ESR，数组的数量、顺序是和芯片内外异常（中断）相对应的。比如，Reset_Handler对应复位中断，NMI_Handler对应NMI。
__Vectors_Size是向量表的size。
PRESERVE8
THUMB
; Vector Table Mapped to Address 0 at Reset
AREA RESET, DATA, READONLY
EXPORT __Vectors
EXPORT __Vectors_End
EXPORT __Vectors_Size
__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 OS_CPU_PendSVHandler ; PendSV Handler
DCD OS_CPU_SysTickHandler ; SysTick Handler
; External Interrupts
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 DMA1_Channel1_IRQHandler ; DMA1 Channel 1
DCD DMA1_Channel2_IRQHandler ; DMA1 Channel 2
DCD DMA1_Channel3_IRQHandler ; DMA1 Channel 3
DCD DMA1_Channel4_IRQHandler ; DMA1 Channel 4
DCD DMA1_Channel5_IRQHandler ; DMA1 Channel 5
DCD DMA1_Channel6_IRQHandler ; DMA1 Channel 6
DCD DMA1_Channel7_IRQHandler ; DMA1 Channel 7
DCD ADC1_2_IRQHandler ; ADC1 & ADC2
DCD USB_HP_CAN1_TX_IRQHandler ; USB High Priority or CAN1 TX
DCD USB_LP_CAN1_RX0_IRQHandler ; USB Low Priority or CAN1 RX0
DCD CAN1_RX1_IRQHandler ; CAN1 RX1
DCD CAN1_SCE_IRQHandler ; CAN1 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
DCD TIM8_BRK_IRQHandler ; TIM8 Break
DCD TIM8_UP_IRQHandler ; TIM8 Update
DCD TIM8_TRG_COM_IRQHandler ; TIM8 Trigger and Commutation
DCD TIM8_CC_IRQHandler ; TIM8 Capture Compare
DCD ADC3_IRQHandler ; ADC3
DCD FSMC_IRQHandler ; FSMC
DCD SDIO_IRQHandler ; SDIO
DCD TIM5_IRQHandler ; TIM5
DCD SPI3_IRQHandler ; SPI3
DCD UART4_IRQHandler ; UART4
DCD UART5_IRQHandler ; UART5
DCD TIM6_IRQHandler ; TIM6
DCD TIM7_IRQHandler ; TIM7
DCD DMA2_Channel1_IRQHandler ; DMA2 Channel1
DCD DMA2_Channel2_IRQHandler ; DMA2 Channel2
DCD DMA2_Channel3_IRQHandler ; DMA2 Channel3
DCD DMA2_Channel4_5_IRQHandler ; DMA2 Channel4 & Channel5
__Vectors_End
__Vectors_Size EQU __Vectors_End - __Vectors
- 函数定义
PROC和ENDP成对使用，用于定义子程序。
[WEAK]是汇编器表示，相当于编译器扩展关键字__weak, 如果同时又[WEAK]和非weak的同名符号，非weak的符号会被优先链接。
AREA |.text|, CODE, READONLY
; Reset handler
Reset_Handler PROC
EXPORT Reset_Handler [WEAK]
IMPORT __main ; extern __main
IMPORT SystemInit ; extern SystemInit
LDR R0, =SystemInit ; SystemInit地址load到R0寄存器
BLX R0 ; 跳转到R0，也就是调用SystemInit()
LDR R0, =__main
BX R0 ；类似，调用__main()，libc会最终调用main()
ENDP
; Dummy Exception Handlers (infinite loops which can be modified)
NMI_Handler PROC
EXPORT NMI_Handler [WEAK]
B . ; . 应该是表示当前位置，跳转到当前位置，类似于死循环
ENDP
HardFault_Handler\
PROC
EXPORT HardFault_Handler [WEAK]
B .
ENDP
MemManage_Handler\
PROC
EXPORT MemManage_Handler [WEAK]
B .
ENDP
BusFault_Handler\
PROC
EXPORT BusFault_Handler [WEAK]
B .
ENDP
UsageFault_Handler\
PROC
EXPORT UsageFault_Handler [WEAK]
B .
ENDP
SVC_Handler PROC
EXPORT SVC_Handler [WEAK]
B .
ENDP
DebugMon_Handler\
PROC
EXPORT DebugMon_Handler [WEAK]
B .
ENDP
OS_CPU_PendSVHandler PROC
EXPORT OS_CPU_PendSVHandler [WEAK]
B .
ENDP
OS_CPU_SysTickHandler PROC
EXPORT OS_CPU_SysTickHandler [WEAK]
B .
ENDP
Default_Handler PROC
EXPORT WWDG_IRQHandler [WEAK]
EXPORT PVD_IRQHandler [WEAK]
EXPORT TAMPER_IRQHandler [WEAK]
EXPORT RTC_IRQHandler [WEAK]
EXPORT FLASH_IRQHandler [WEAK]
EXPORT RCC_IRQHandler [WEAK]
EXPORT EXTI0_IRQHandler [WEAK]
EXPORT EXTI1_IRQHandler [WEAK]
EXPORT EXTI2_IRQHandler [WEAK]
EXPORT EXTI3_IRQHandler [WEAK]
EXPORT EXTI4_IRQHandler [WEAK]
EXPORT DMA1_Channel1_IRQHandler [WEAK]
EXPORT DMA1_Channel2_IRQHandler [WEAK]
EXPORT DMA1_Channel3_IRQHandler [WEAK]
EXPORT DMA1_Channel4_IRQHandler [WEAK]
EXPORT DMA1_Channel5_IRQHandler [WEAK]
EXPORT DMA1_Channel6_IRQHandler [WEAK]
EXPORT DMA1_Channel7_IRQHandler [WEAK]
EXPORT ADC1_2_IRQHandler [WEAK]
EXPORT USB_HP_CAN1_TX_IRQHandler [WEAK]
EXPORT USB_LP_CAN1_RX0_IRQHandler [WEAK]
EXPORT CAN1_RX1_IRQHandler [WEAK]
EXPORT CAN1_SCE_IRQHandler [WEAK]
EXPORT EXTI9_5_IRQHandler [WEAK]
EXPORT TIM1_BRK_IRQHandler [WEAK]
EXPORT TIM1_UP_IRQHandler [WEAK]
EXPORT TIM1_TRG_COM_IRQHandler [WEAK]
EXPORT TIM1_CC_IRQHandler [WEAK]
EXPORT TIM2_IRQHandler [WEAK]
EXPORT TIM3_IRQHandler [WEAK]
EXPORT TIM4_IRQHandler [WEAK]
EXPORT I2C1_EV_IRQHandler [WEAK]
EXPORT I2C1_ER_IRQHandler [WEAK]
EXPORT I2C2_EV_IRQHandler [WEAK]
EXPORT I2C2_ER_IRQHandler [WEAK]
EXPORT SPI1_IRQHandler [WEAK]
EXPORT SPI2_IRQHandler [WEAK]
EXPORT USART1_IRQHandler [WEAK]
EXPORT USART2_IRQHandler [WEAK]
EXPORT USART3_IRQHandler [WEAK]
EXPORT EXTI15_10_IRQHandler [WEAK]
EXPORT RTCAlarm_IRQHandler [WEAK]
EXPORT USBWakeUp_IRQHandler [WEAK]
EXPORT TIM8_BRK_IRQHandler [WEAK]
EXPORT TIM8_UP_IRQHandler [WEAK]
EXPORT TIM8_TRG_COM_IRQHandler [WEAK]
EXPORT TIM8_CC_IRQHandler [WEAK]
EXPORT ADC3_IRQHandler [WEAK]
EXPORT FSMC_IRQHandler [WEAK]
EXPORT SDIO_IRQHandler [WEAK]
EXPORT TIM5_IRQHandler [WEAK]
EXPORT SPI3_IRQHandler [WEAK]
EXPORT UART4_IRQHandler [WEAK]
EXPORT UART5_IRQHandler [WEAK]
EXPORT TIM6_IRQHandler [WEAK]
EXPORT TIM7_IRQHandler [WEAK]
EXPORT DMA2_Channel1_IRQHandler [WEAK]
EXPORT DMA2_Channel2_IRQHandler [WEAK]
EXPORT DMA2_Channel3_IRQHandler [WEAK]
EXPORT DMA2_Channel4_5_IRQHandler [WEAK]
WWDG_IRQHandler
PVD_IRQHandler
TAMPER_IRQHandler
RTC_IRQHandler
FLASH_IRQHandler
RCC_IRQHandler
EXTI0_IRQHandler
EXTI1_IRQHandler
EXTI2_IRQHandler
EXTI3_IRQHandler
EXTI4_IRQHandler
DMA1_Channel1_IRQHandler
DMA1_Channel2_IRQHandler
DMA1_Channel3_IRQHandler
DMA1_Channel4_IRQHandler
DMA1_Channel5_IRQHandler
DMA1_Channel6_IRQHandler
DMA1_Channel7_IRQHandler
ADC1_2_IRQHandler
USB_HP_CAN1_TX_IRQHandler
USB_LP_CAN1_RX0_IRQHandler
CAN1_RX1_IRQHandler
CAN1_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
TIM8_BRK_IRQHandler
TIM8_UP_IRQHandler
TIM8_TRG_COM_IRQHandler
TIM8_CC_IRQHandler
ADC3_IRQHandler
FSMC_IRQHandler
SDIO_IRQHandler
TIM5_IRQHandler
SPI3_IRQHandler
UART4_IRQHandler
UART5_IRQHandler
TIM6_IRQHandler
TIM7_IRQHandler
DMA2_Channel1_IRQHandler
DMA2_Channel2_IRQHandler
DMA2_Channel3_IRQHandler
DMA2_Channel4_5_IRQHandler
B .
ENDP
ALIGN
- 堆栈初始化
;*******************************************************************************
; User Stack and Heap initialization
;*******************************************************************************
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
ALIGN
ENDIF
END
ARM工具链提供了两个运行时内存模型：
1. `one-region run-time memory model` (单区模型)：
堆栈共用同一块内存区域，堆栈以相反的方向增长。
one-region run-time memory model
2. `two-region run-time memory model` （双区模型）：
堆栈使用相互独立的内存区域。使用双区模型时，必须import __use_two_region_memory
two-region run-time memory model
那么具体如何初始化堆栈呢？在ARM文档(keil自带)中有描述(3种方式)：
If you are using the C library's initialization code, use any of the following methods to configure the stack and heap:
Use the symbols __initial_sp, __heap_base, and __heap_limit.
Use a scatter file to define ARM_LIB_STACKHEAP, ARM_LIB_STACK, or ARM_LIB_HEAP regions.
Implement __user_setup_stackheap() or __user_initial_stackheap().
方法1：
Use the symbols __initial_sp, __heap_base, and __heap_limit
IF :DEF:__MICROLIB包含的代码就是使用的方法1，就是当前keil中勾选了使用micro lib时，就会通过__initial_sp, __heap_base, and __heap_limit来配置堆栈。-
方法2：
Use a scatter file to define ARM_LIB_STACKHEAP, ARM_LIB_STACK, or ARM_LIB_HEAP regions.
分散加载宏定义两个执行域：ARM_LIB_HEAP and ARM_LIB_STACK,两个域都需要配置EMPTY属性，则c库__user_setup_stackheap()不会采用默认实现，而是会通过如下符号来初始化堆栈：Image$$ARM_LIB_STACK$$ZI$$Base. Image$$ARM_LIB_STACK$$ZI$$Limit. Image$$ARM_LIB_HEAP$$ZI$$Base. Image$$ARM_LIB_HEAP$$ZI$$Limit分散加载文件配置示例：
LOAD_FLASH … { … ARM_LIB_STACK 0x40000 EMPTY -0x20000 ; Stack region growing down { } ARM_LIB_HEAP 0x28000000 EMPTY 0x80000 ; Heap region growing up { } … } 方法3：
Implement __user_setup_stackheap() or __user_initial_stackheap()