STM32启动代码注释

相应的视频教程：https://www.bilibili.com/video/BV1pW411p7ae?p=1

;******************************************************************************
;* File Name          : startup_stm32l010x4.s
;* Author             : MCD Application Team
;* Description        : STM32l010x4 Devices vector table for MDK-ARM toolchain.
;*                      This module performs:
;*                      - Set the initial SP
;*                      - Set the initial PC == Reset_Handler
;*                      - Set the vector table entries with the exceptions ISR address
;*                      - Branches to __main in the C library (which eventually
;*                        calls main()).
;*                      After Reset the Cortex-M0+ processor is in Thread mode,
;*                      priority is Privileged, and the Stack is set to Main.
;******************************************************************************
;* @attention
;*
;* Copyright (c) 2016 STMicroelectronics.
;* All rights reserved.
;*
;* This software component is licensed by ST under BSD 3-Clause license,
;* the "License"; You may not use this file except in compliance with the
;* License. You may obtain a copy of the License at:
;*                        opensource.org/licenses/BSD-3-Clause
;*
;******************************************************************************

; Amount of memory (in bytes) allocated for Stack
; Tailor this value to your application needs
; <h> Stack Configuration
;   <o> Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>

Stack_Size        EQU     0x400  ;EQU伪指令，相当于宏定义，即#define Stack_Size 0x400

                AREA    STACK, NOINIT, READWRITE, ALIGN=3 ;AREA伪指令，用于定义代码段或数据段。STACK表段名，NOINIT表不初始化，READWRITE可读可写，ALIGN按2^3字节对齐
Stack_Mem       SPACE   Stack_Size                        ;SPACE用于分配一定大小的内存空间，单位为子节
__initial_sp                                              ;__initial_sp紧挨着SPACE语句，表示栈的结束地址。也就是栈顶的地址


; <h> Heap Configuration
;   <o>  Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>

Heap_Size      EQU     0x200

                AREA    HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base                                              ;在SPACE前出现这条代码代表的是堆的起始地址
Heap_Mem        SPACE   Heap_Size
__heap_limit                                             ;在SPACE后出现这条代码代表的是堆的结束地址

                PRESERVE8                                ;指定当前文件的堆栈按照 8 字节对齐
                THUMB                                    ;表示后面指令兼容 THUMB 指令


; 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开辟以字为单位的内存，四子节对齐，并要求初始化
                DCD     Reset_Handler             ; Reset Handler
                DCD     NMI_Handler               ; NMI Handler
                DCD     HardFault_Handler         ; Hard Fault Handler
                DCD     0                         ; Reserved
                DCD     0                         ; Reserved
                DCD     0                         ; Reserved
                DCD     0                         ; Reserved
                DCD     0                         ; Reserved
                DCD     0                         ; Reserved
                DCD     0                         ; Reserved
                DCD     SVC_Handler               ; SVCall Handler
                DCD     0                         ; Reserved
                DCD     0                         ; Reserved
                DCD     PendSV_Handler            ; PendSV Handler
                DCD     SysTick_Handler           ; SysTick Handler

                ; External Interrupts
                DCD     WWDG_IRQHandler                ; Window Watchdog
                DCD     0                              ; Reserved
                DCD     RTC_IRQHandler                 ; RTC through EXTI Line
                DCD     FLASH_IRQHandler               ; FLASH
                DCD     RCC_IRQHandler                 ; RCC
                DCD     EXTI0_1_IRQHandler             ; EXTI Line 0 and 1
                DCD     EXTI2_3_IRQHandler             ; EXTI Line 2 and 3
                DCD     EXTI4_15_IRQHandler            ; EXTI Line 4 to 15
                DCD     0                              ; Reserved
                DCD     DMA1_Channel1_IRQHandler       ; DMA1 Channel 1
                DCD     DMA1_Channel2_3_IRQHandler     ; DMA1 Channel 2 and Channel 3
                DCD     DMA1_Channel4_5_IRQHandler     ; DMA1 Channel 4 and Channel 5
                DCD     ADC1_IRQHandler                ; ADC1
                DCD     LPTIM1_IRQHandler              ; LPTIM1
                DCD     0                              ; Reserved
                DCD     TIM2_IRQHandler                ; TIM2
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     TIM21_IRQHandler               ; TIM21
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     I2C1_IRQHandler                ; I2C1
                DCD     0                              ; Reserved
                DCD     SPI1_IRQHandler                ; SPI1
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     USART2_IRQHandler              ; USART2
                DCD     LPUART1_IRQHandler             ; LPUART1
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
   
__Vectors_End

__Vectors_Size  EQU  __Vectors_End - __Vectors

                AREA    |.text|, CODE, READONLY

; Reset handler routine
Reset_Handler    PROC  ;PROC和ENDP伪指令，把程序段分成若干个过程，使程序结构更加清晰
                 EXPORT  Reset_Handler                 [WEAK]
        IMPORT  __main
        IMPORT  SystemInit

        LDR     R0, =__initial_sp          ; set stack pointer
        MSR     MSP, R0

;;Check if boot space corresponds to system memory

        LDR R0,=0x00000004    ;04地址存放了Reset_Handler地址
        LDR R1, [R0]          ;Reset_Handler地址有可能是0x2000 0000左右(sram启动)，也有可能是0x0800 0000左右(flash启动)，也有可能是0x1fff ec00左右(system memory启动)
        LSRS R1, R1, #24      ;Reset_Handler地址向右移动24bit，剩余高八位移到低八位
        LDR R2,=0x1F        
        CMP R1, R2            ;相等则说明是从system memory启动(串口启动)

        BNE ApplicationStart  ;不相等则跳到ApplicationStart

;; SYSCFG clock enable

        LDR R0,=0x40021034    ;如果是串口启动则从这里开始执行，主要是配置一些时钟
        LDR R1,=0x00000001
        STR R1, [R0]

;; Set CFGR1 register with flash memory remap at address 0  ;CFGR1是时钟配置寄存器

        LDR R0,=0x40010000
        LDR R1,=0x00000000
        STR R1, [R0]

ApplicationStart
                 LDR     R0, =SystemInit   ;主要在这里面进行时钟配置，该函数定义在system_stm3210xx.c中
                 BLX     R0                ;BLX可以返回的跳转，使程序跳转到R0指示的位置处，并将PC中的内容保存到R14中
                 
                 ;__main地址装入R0寄存器，该函数为编译系统提供的c/c++标准库函数里的一个初始化子程序
                 ;__main函数主要处理两个工作：1、完成映象文件的初始化工作。2、调用_rt_entry库函数进入到用户程序。
                 ;__main是一个库函数，在它调用的_rt_entry函数的第一条指令就是调用本程序的__user_initial_stackheap函数，初始化代码的堆和栈，
                 ;然后初始化C运行库，接下来调用用户的main()函数
                 LDR     R0, =__main
                 BX      R0                ;BX,不返回的跳转
                 ENDP

; Dummy Exception Handlers (infinite loops which can be modified)

NMI_Handler     PROC
                EXPORT  NMI_Handler                    [WEAK]  ;弱声明
                B       .             ; "B   ."表示程序跳转到此处，也就是不停在本行跳转，即死循环
                ENDP
HardFault_Handler
                PROC
                EXPORT  HardFault_Handler              [WEAK]
                B       .
                ENDP
SVC_Handler     PROC
                EXPORT  SVC_Handler                    [WEAK]
                B       .
                ENDP
PendSV_Handler  PROC
                EXPORT  PendSV_Handler                 [WEAK]
                B       .
                ENDP
SysTick_Handler PROC
                EXPORT  SysTick_Handler                [WEAK]
                B       .
                ENDP

Default_Handler PROC

                EXPORT  WWDG_IRQHandler                [WEAK]
                EXPORT  RTC_IRQHandler                 [WEAK]
                EXPORT  FLASH_IRQHandler               [WEAK]
                EXPORT  RCC_IRQHandler                 [WEAK]
                EXPORT  EXTI0_1_IRQHandler             [WEAK]
                EXPORT  EXTI2_3_IRQHandler             [WEAK]
                EXPORT  EXTI4_15_IRQHandler            [WEAK]
                EXPORT  DMA1_Channel1_IRQHandler       [WEAK]
                EXPORT  DMA1_Channel2_3_IRQHandler     [WEAK]
                EXPORT  DMA1_Channel4_5_IRQHandler     [WEAK]
                EXPORT  ADC1_IRQHandler                [WEAK]
                EXPORT  LPTIM1_IRQHandler              [WEAK]
                EXPORT  TIM2_IRQHandler                [WEAK]
                EXPORT  TIM21_IRQHandler               [WEAK]
                EXPORT  I2C1_IRQHandler                [WEAK]
                EXPORT  SPI1_IRQHandler                [WEAK]
                EXPORT  USART2_IRQHandler              [WEAK]
                EXPORT  LPUART1_IRQHandler             [WEAK]

WWDG_IRQHandler
RTC_IRQHandler
FLASH_IRQHandler
RCC_IRQHandler
EXTI0_1_IRQHandler
EXTI2_3_IRQHandler
EXTI4_15_IRQHandler
DMA1_Channel1_IRQHandler
DMA1_Channel2_3_IRQHandler
DMA1_Channel4_5_IRQHandler
ADC1_IRQHandler 
LPTIM1_IRQHandler
TIM2_IRQHandler
TIM21_IRQHandler
I2C1_IRQHandler
SPI1_IRQHandler
USART2_IRQHandler
LPUART1_IRQHandler

                B       .    ;以上这些中断任何一个发生了，都会来执行这条死循环指令

                ENDP

                ALIGN

;*******************************************************************************
; 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

;************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE*****