startup_stm32f405xx.S文件解读

一、代码全文

/**
  ******************************************************************************
  * @file      startup_stm32f405xx.s
  * @author    MCD Application Team
  * @brief     STM32F405xx Devices vector table for GCC based toolchains. 
  *            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-M4 processor is in Thread mode,
  *            priority is Privileged, and the Stack is set to Main.
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; COPYRIGHT 2017 STMicroelectronics</center></h2>
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *   1. Redistributions of source code must retain the above copyright notice,
  *      this list of conditions and the following disclaimer.
  *   2. Redistributions in binary form must reproduce the above copyright notice,
  *      this list of conditions and the following disclaimer in the documentation
  *      and/or other materials provided with the distribution.
  *   3. Neither the name of STMicroelectronics nor the names of its contributors
  *      may be used to endorse or promote products derived from this software
  *      without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  ******************************************************************************
  */
    
  .syntax unified
  .cpu cortex-m4
  .fpu softvfp
  .thumb

.global  g_pfnVectors
.global  Default_Handler

/* start address for the initialization values of the .data section. 
defined in linker script */
.word  _sidata
/* start address for the .data section. defined in linker script */  
.word  _sdata
/* end address for the .data section. defined in linker script */
.word  _edata
/* start address for the .bss section. defined in linker script */
.word  _sbss
/* end address for the .bss section. defined in linker script */
.word  _ebss
/* stack used for SystemInit_ExtMemCtl; always internal RAM used */

/**
 * @brief  This is the code that gets called when the processor first
 *          starts execution following a reset event. Only the absolutely
 *          necessary set is performed, after which the application
 *          supplied main() routine is called. 
 * @param  None
 * @retval : None
*/

    .section  .text.Reset_Handler
  .weak  Reset_Handler
  .type  Reset_Handler, %function
Reset_Handler:  
  ldr   sp, =_estack     /* set stack pointer */

/* Copy the data segment initializers from flash to SRAM */  
  movs  r1, #0
  b  LoopCopyDataInit

CopyDataInit:
  ldr  r3, =_sidata
  ldr  r3, [r3, r1]
  str  r3, [r0, r1]
  adds  r1, r1, #4
    
LoopCopyDataInit:
  ldr  r0, =_sdata
  ldr  r3, =_edata
  adds  r2, r0, r1
  cmp  r2, r3
  bcc  CopyDataInit
  ldr  r2, =_sbss
  b  LoopFillZerobss
/* Zero fill the bss segment. */  
FillZerobss:
  movs  r3, #0
  str  r3, [r2], #4
    
LoopFillZerobss:
  ldr  r3, = _ebss
  cmp  r2, r3
  bcc  FillZerobss

/* Call the clock system intitialization function.*/
  bl  SystemInit   
/* Call static constructors */
    /* bl __libc_init_array */
/* Call the application's entry point.*/
  bl  entry
  bx  lr    
.size  Reset_Handler, .-Reset_Handler

/**
 * @brief  This is the code that gets called when the processor receives an 
 *         unexpected interrupt.  This simply enters an infinite loop, preserving
 *         the system state for examination by a debugger.
 * @param  None     
 * @retval None       
*/
    .section  .text.Default_Handler,"ax",%progbits
Default_Handler:
Infinite_Loop:
  b  Infinite_Loop
  .size  Default_Handler, .-Default_Handler
/******************************************************************************
*
* The minimal vector table for a Cortex M3. Note that the proper constructs
* must be placed on this to ensure that it ends up at physical address
* 0x0000.0000.
* 
*******************************************************************************/
   .section  .isr_vector,"a",%progbits
  .type  g_pfnVectors, %object
  .size  g_pfnVectors, .-g_pfnVectors
    

	
g_pfnVectors:
  .word  _estack
  .word  Reset_Handler

  .word  NMI_Handler
  .word  HardFault_Handler
  .word  MemManage_Handler
  .word  BusFault_Handler
  .word  UsageFault_Handler
  .word  0
  .word  0
  .word  0
  .word  0
  .word  SVC_Handler
  .word  DebugMon_Handler
  .word  0
  .word  PendSV_Handler
  .word  SysTick_Handler
  
  /* External Interrupts */
  .word     WWDG_IRQHandler                   /* Window WatchDog              */                                        
  .word     PVD_IRQHandler                    /* PVD through EXTI Line detection */                        
  .word     TAMP_STAMP_IRQHandler             /* Tamper and TimeStamps through the EXTI line */            
  .word     RTC_WKUP_IRQHandler               /* RTC Wakeup through the EXTI line */                      
  .word     FLASH_IRQHandler                  /* FLASH                        */                                          
  .word     RCC_IRQHandler                    /* RCC                          */                                            
  .word     EXTI0_IRQHandler                  /* EXTI Line0                   */                        
  .word     EXTI1_IRQHandler                  /* EXTI Line1                   */                          
  .word     EXTI2_IRQHandler                  /* EXTI Line2                   */                          
  .word     EXTI3_IRQHandler                  /* EXTI Line3                   */                          
  .word     EXTI4_IRQHandler                  /* EXTI Line4                   */                          
  .word     DMA1_Stream0_IRQHandler           /* DMA1 Stream 0                */                  
  .word     DMA1_Stream1_IRQHandler           /* DMA1 Stream 1                */                   
  .word     DMA1_Stream2_IRQHandler           /* DMA1 Stream 2                */                   
  .word     DMA1_Stream3_IRQHandler           /* DMA1 Stream 3                */                   
  .word     DMA1_Stream4_IRQHandler           /* DMA1 Stream 4                */                   
  .word     DMA1_Stream5_IRQHandler           /* DMA1 Stream 5                */                   
  .word     DMA1_Stream6_IRQHandler           /* DMA1 Stream 6                */                   
  .word     ADC_IRQHandler                    /* ADC1, ADC2 and ADC3s         */                   
  .word     CAN1_TX_IRQHandler                /* CAN1 TX                      */                         
  .word     CAN1_RX0_IRQHandler               /* CAN1 RX0                     */                          
  .word     CAN1_RX1_IRQHandler               /* CAN1 RX1                     */                          
  .word     CAN1_SCE_IRQHandler               /* CAN1 SCE                     */                          
  .word     EXTI9_5_IRQHandler                /* External Line[9:5]s          */                          
  .word     TIM1_BRK_TIM9_IRQHandler          /* TIM1 Break and TIM9          */         
  .word     TIM1_UP_TIM10_IRQHandler          /* TIM1 Update and TIM10        */         
  .word     TIM1_TRG_COM_TIM11_IRQHandler     /* TIM1 Trigger and Commutation and TIM11 */
  .word     TIM1_CC_IRQHandler                /* TIM1 Capture Compare         */                          
  .word     TIM2_IRQHandler                   /* TIM2                         */                   
  .word     TIM3_IRQHandler                   /* TIM3                         */                   
  .word     TIM4_IRQHandler                   /* TIM4                         */                   
  .word     I2C1_EV_IRQHandler                /* I2C1 Event                   */                          
  .word     I2C1_ER_IRQHandler                /* I2C1 Error                   */                          
  .word     I2C2_EV_IRQHandler                /* I2C2 Event                   */                          
  .word     I2C2_ER_IRQHandler                /* I2C2 Error                   */                            
  .word     SPI1_IRQHandler                   /* SPI1                         */                   
  .word     SPI2_IRQHandler                   /* SPI2                         */                   
  .word     USART1_IRQHandler                 /* USART1                       */                   
  .word     USART2_IRQHandler                 /* USART2                       */                   
  .word     USART3_IRQHandler                 /* USART3                       */                   
  .word     EXTI15_10_IRQHandler              /* External Line[15:10]s        */                          
  .word     RTC_Alarm_IRQHandler              /* RTC Alarm (A and B) through EXTI Line */                 
  .word     OTG_FS_WKUP_IRQHandler            /* USB OTG FS Wakeup through EXTI line */                       
  .word     TIM8_BRK_TIM12_IRQHandler         /* TIM8 Break and TIM12         */         
  .word     TIM8_UP_TIM13_IRQHandler          /* TIM8 Update and TIM13        */         
  .word     TIM8_TRG_COM_TIM14_IRQHandler     /* TIM8 Trigger and Commutation and TIM14 */
  .word     TIM8_CC_IRQHandler                /* TIM8 Capture Compare         */                          
  .word     DMA1_Stream7_IRQHandler           /* DMA1 Stream7                 */                          
  .word     FSMC_IRQHandler                   /* FSMC                         */                   
  .word     SDIO_IRQHandler                   /* SDIO                         */                   
  .word     TIM5_IRQHandler                   /* TIM5                         */                   
  .word     SPI3_IRQHandler                   /* SPI3                         */                   
  .word     UART4_IRQHandler                  /* UART4                        */                   
  .word     UART5_IRQHandler                  /* UART5                        */                   
  .word     TIM6_DAC_IRQHandler               /* TIM6 and DAC1&2 underrun errors */                   
  .word     TIM7_IRQHandler                   /* TIM7                         */
  .word     DMA2_Stream0_IRQHandler           /* DMA2 Stream 0                */                   
  .word     DMA2_Stream1_IRQHandler           /* DMA2 Stream 1                */                   
  .word     DMA2_Stream2_IRQHandler           /* DMA2 Stream 2                */                   
  .word     DMA2_Stream3_IRQHandler           /* DMA2 Stream 3                */                   
  .word     DMA2_Stream4_IRQHandler           /* DMA2 Stream 4                */                   
  .word     0                                 /* Reserved                     */                   
  .word     0                                 /* Reserved                     */                     
  .word     CAN2_TX_IRQHandler                /* CAN2 TX                      */                          
  .word     CAN2_RX0_IRQHandler               /* CAN2 RX0                     */                          
  .word     CAN2_RX1_IRQHandler               /* CAN2 RX1                     */                          
  .word     CAN2_SCE_IRQHandler               /* CAN2 SCE                     */                          
  .word     OTG_FS_IRQHandler                 /* USB OTG FS                   */                   
  .word     DMA2_Stream5_IRQHandler           /* DMA2 Stream 5                */                   
  .word     DMA2_Stream6_IRQHandler           /* DMA2 Stream 6                */                   
  .word     DMA2_Stream7_IRQHandler           /* DMA2 Stream 7                */                   
  .word     USART6_IRQHandler                 /* USART6                       */                    
  .word     I2C3_EV_IRQHandler                /* I2C3 event                   */                          
  .word     I2C3_ER_IRQHandler                /* I2C3 error                   */                          
  .word     OTG_HS_EP1_OUT_IRQHandler         /* USB OTG HS End Point 1 Out   */                   
  .word     OTG_HS_EP1_IN_IRQHandler          /* USB OTG HS End Point 1 In    */                   
  .word     OTG_HS_WKUP_IRQHandler            /* USB OTG HS Wakeup through EXTI */                         
  .word     OTG_HS_IRQHandler                 /* USB OTG HS                   */                   
  .word     0                                 /* Reserved                         */                   
  .word     0                                 /* Reserved                  */                   
  .word     HASH_RNG_IRQHandler               /* Hash and Rng                 */
  .word     FPU_IRQHandler                    /* FPU                          */

                      
/*******************************************************************************
*
* Provide weak aliases for each Exception handler to the Default_Handler. 
* As they are weak aliases, any function with the same name will override 
* this definition.
* 
*******************************************************************************/
   .weak      NMI_Handler
   .thumb_set NMI_Handler,Default_Handler
  
   .weak      HardFault_Handler
   .thumb_set HardFault_Handler,Default_Handler
  
   .weak      MemManage_Handler
   .thumb_set MemManage_Handler,Default_Handler
  
   .weak      BusFault_Handler
   .thumb_set BusFault_Handler,Default_Handler

   .weak      UsageFault_Handler
   .thumb_set UsageFault_Handler,Default_Handler

   .weak      SVC_Handler
   .thumb_set SVC_Handler,Default_Handler

   .weak      DebugMon_Handler
   .thumb_set DebugMon_Handler,Default_Handler

   .weak      PendSV_Handler
   .thumb_set PendSV_Handler,Default_Handler

   .weak      SysTick_Handler
   .thumb_set SysTick_Handler,Default_Handler              
  
   .weak      WWDG_IRQHandler                   
   .thumb_set WWDG_IRQHandler,Default_Handler      
                  
   .weak      PVD_IRQHandler      
   .thumb_set PVD_IRQHandler,Default_Handler
               
   .weak      TAMP_STAMP_IRQHandler            
   .thumb_set TAMP_STAMP_IRQHandler,Default_Handler
            
   .weak      RTC_WKUP_IRQHandler                  
   .thumb_set RTC_WKUP_IRQHandler,Default_Handler
            
   .weak      FLASH_IRQHandler         
   .thumb_set FLASH_IRQHandler,Default_Handler
                  
   .weak      RCC_IRQHandler      
   .thumb_set RCC_IRQHandler,Default_Handler
                  
   .weak      EXTI0_IRQHandler         
   .thumb_set EXTI0_IRQHandler,Default_Handler
                  
   .weak      EXTI1_IRQHandler         
   .thumb_set EXTI1_IRQHandler,Default_Handler
                     
   .weak      EXTI2_IRQHandler         
   .thumb_set EXTI2_IRQHandler,Default_Handler 
                 
   .weak      EXTI3_IRQHandler         
   .thumb_set EXTI3_IRQHandler,Default_Handler
                        
   .weak      EXTI4_IRQHandler         
   .thumb_set EXTI4_IRQHandler,Default_Handler
                  
   .weak      DMA1_Stream0_IRQHandler               
   .thumb_set DMA1_Stream0_IRQHandler,Default_Handler
         
   .weak      DMA1_Stream1_IRQHandler               
   .thumb_set DMA1_Stream1_IRQHandler,Default_Handler
                  
   .weak      DMA1_Stream2_IRQHandler               
   .thumb_set DMA1_Stream2_IRQHandler,Default_Handler
                  
   .weak      DMA1_Stream3_IRQHandler               
   .thumb_set DMA1_Stream3_IRQHandler,Default_Handler 
                 
   .weak      DMA1_Stream4_IRQHandler              
   .thumb_set DMA1_Stream4_IRQHandler,Default_Handler
                  
   .weak      DMA1_Stream5_IRQHandler               
   .thumb_set DMA1_Stream5_IRQHandler,Default_Handler
                  
   .weak      DMA1_Stream6_IRQHandler               
   .thumb_set DMA1_Stream6_IRQHandler,Default_Handler
                  
   .weak      ADC_IRQHandler      
   .thumb_set ADC_IRQHandler,Default_Handler
               
   .weak      CAN1_TX_IRQHandler   
   .thumb_set CAN1_TX_IRQHandler,Default_Handler
            
   .weak      CAN1_RX0_IRQHandler                  
   .thumb_set CAN1_RX0_IRQHandler,Default_Handler
                           
   .weak      CAN1_RX1_IRQHandler                  
   .thumb_set CAN1_RX1_IRQHandler,Default_Handler
            
   .weak      CAN1_SCE_IRQHandler                  
   .thumb_set CAN1_SCE_IRQHandler,Default_Handler
            
   .weak      EXTI9_5_IRQHandler   
   .thumb_set EXTI9_5_IRQHandler,Default_Handler
            
   .weak      TIM1_BRK_TIM9_IRQHandler            
   .thumb_set TIM1_BRK_TIM9_IRQHandler,Default_Handler
            
   .weak      TIM1_UP_TIM10_IRQHandler            
   .thumb_set TIM1_UP_TIM10_IRQHandler,Default_Handler
      
   .weak      TIM1_TRG_COM_TIM11_IRQHandler      
   .thumb_set TIM1_TRG_COM_TIM11_IRQHandler,Default_Handler
      
   .weak      TIM1_CC_IRQHandler   
   .thumb_set TIM1_CC_IRQHandler,Default_Handler
                  
   .weak      TIM2_IRQHandler            
   .thumb_set TIM2_IRQHandler,Default_Handler
                  
   .weak      TIM3_IRQHandler            
   .thumb_set TIM3_IRQHandler,Default_Handler
                  
   .weak      TIM4_IRQHandler            
   .thumb_set TIM4_IRQHandler,Default_Handler
                  
   .weak      I2C1_EV_IRQHandler   
   .thumb_set I2C1_EV_IRQHandler,Default_Handler
                     
   .weak      I2C1_ER_IRQHandler   
   .thumb_set I2C1_ER_IRQHandler,Default_Handler
                     
   .weak      I2C2_EV_IRQHandler   
   .thumb_set I2C2_EV_IRQHandler,Default_Handler
                  
   .weak      I2C2_ER_IRQHandler   
   .thumb_set I2C2_ER_IRQHandler,Default_Handler
                           
   .weak      SPI1_IRQHandler            
   .thumb_set SPI1_IRQHandler,Default_Handler
                        
   .weak      SPI2_IRQHandler            
   .thumb_set SPI2_IRQHandler,Default_Handler
                  
   .weak      USART1_IRQHandler      
   .thumb_set USART1_IRQHandler,Default_Handler
                     
   .weak      USART2_IRQHandler      
   .thumb_set USART2_IRQHandler,Default_Handler
                     
   .weak      USART3_IRQHandler      
   .thumb_set USART3_IRQHandler,Default_Handler
                  
   .weak      EXTI15_10_IRQHandler               
   .thumb_set EXTI15_10_IRQHandler,Default_Handler
               
   .weak      RTC_Alarm_IRQHandler               
   .thumb_set RTC_Alarm_IRQHandler,Default_Handler
            
   .weak      OTG_FS_WKUP_IRQHandler         
   .thumb_set OTG_FS_WKUP_IRQHandler,Default_Handler
            
   .weak      TIM8_BRK_TIM12_IRQHandler         
   .thumb_set TIM8_BRK_TIM12_IRQHandler,Default_Handler
         
   .weak      TIM8_UP_TIM13_IRQHandler            
   .thumb_set TIM8_UP_TIM13_IRQHandler,Default_Handler
         
   .weak      TIM8_TRG_COM_TIM14_IRQHandler      
   .thumb_set TIM8_TRG_COM_TIM14_IRQHandler,Default_Handler
      
   .weak      TIM8_CC_IRQHandler   
   .thumb_set TIM8_CC_IRQHandler,Default_Handler
                  
   .weak      DMA1_Stream7_IRQHandler               
   .thumb_set DMA1_Stream7_IRQHandler,Default_Handler
                     
   .weak      FSMC_IRQHandler            
   .thumb_set FSMC_IRQHandler,Default_Handler
                     
   .weak      SDIO_IRQHandler            
   .thumb_set SDIO_IRQHandler,Default_Handler
                     
   .weak      TIM5_IRQHandler            
   .thumb_set TIM5_IRQHandler,Default_Handler
                     
   .weak      SPI3_IRQHandler            
   .thumb_set SPI3_IRQHandler,Default_Handler
                     
   .weak      UART4_IRQHandler         
   .thumb_set UART4_IRQHandler,Default_Handler
                  
   .weak      UART5_IRQHandler         
   .thumb_set UART5_IRQHandler,Default_Handler
                  
   .weak      TIM6_DAC_IRQHandler                  
   .thumb_set TIM6_DAC_IRQHandler,Default_Handler
               
   .weak      TIM7_IRQHandler            
   .thumb_set TIM7_IRQHandler,Default_Handler
         
   .weak      DMA2_Stream0_IRQHandler               
   .thumb_set DMA2_Stream0_IRQHandler,Default_Handler
               
   .weak      DMA2_Stream1_IRQHandler               
   .thumb_set DMA2_Stream1_IRQHandler,Default_Handler
                  
   .weak      DMA2_Stream2_IRQHandler               
   .thumb_set DMA2_Stream2_IRQHandler,Default_Handler
            
   .weak      DMA2_Stream3_IRQHandler               
   .thumb_set DMA2_Stream3_IRQHandler,Default_Handler
            
   .weak      DMA2_Stream4_IRQHandler               
   .thumb_set DMA2_Stream4_IRQHandler,Default_Handler
            
   .weak      CAN2_TX_IRQHandler   
   .thumb_set CAN2_TX_IRQHandler,Default_Handler
                           
   .weak      CAN2_RX0_IRQHandler                  
   .thumb_set CAN2_RX0_IRQHandler,Default_Handler
                           
   .weak      CAN2_RX1_IRQHandler                  
   .thumb_set CAN2_RX1_IRQHandler,Default_Handler
                           
   .weak      CAN2_SCE_IRQHandler                  
   .thumb_set CAN2_SCE_IRQHandler,Default_Handler
                           
   .weak      OTG_FS_IRQHandler      
   .thumb_set OTG_FS_IRQHandler,Default_Handler
                     
   .weak      DMA2_Stream5_IRQHandler               
   .thumb_set DMA2_Stream5_IRQHandler,Default_Handler
                  
   .weak      DMA2_Stream6_IRQHandler               
   .thumb_set DMA2_Stream6_IRQHandler,Default_Handler
                  
   .weak      DMA2_Stream7_IRQHandler               
   .thumb_set DMA2_Stream7_IRQHandler,Default_Handler
                  
   .weak      USART6_IRQHandler      
   .thumb_set USART6_IRQHandler,Default_Handler
                        
   .weak      I2C3_EV_IRQHandler   
   .thumb_set I2C3_EV_IRQHandler,Default_Handler
                        
   .weak      I2C3_ER_IRQHandler   
   .thumb_set I2C3_ER_IRQHandler,Default_Handler
                        
   .weak      OTG_HS_EP1_OUT_IRQHandler         
   .thumb_set OTG_HS_EP1_OUT_IRQHandler,Default_Handler
               
   .weak      OTG_HS_EP1_IN_IRQHandler            
   .thumb_set OTG_HS_EP1_IN_IRQHandler,Default_Handler
               
   .weak      OTG_HS_WKUP_IRQHandler         
   .thumb_set OTG_HS_WKUP_IRQHandler,Default_Handler
            
   .weak      OTG_HS_IRQHandler      
   .thumb_set OTG_HS_IRQHandler,Default_Handler
                                                     
   .weak      HASH_RNG_IRQHandler                  
   .thumb_set HASH_RNG_IRQHandler,Default_Handler   

   .weak      FPU_IRQHandler                  
   .thumb_set FPU_IRQHandler,Default_Handler  

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

二、代码解读

.syntax unified

这一指令用于指定汇编语法。unified 表示使用统一语法，这种语法兼容 ARM 和 Thumb 指令集，使得在同一文件中可以混合使用两种指令。

.cpu cortex-m4

该指令告知汇编器目标处理器为 Cortex-M4。这会影响生成的指令和处理器特性，因为不同的 ARM 处理器架构支持不同的指令集和功能。

.fpu softvfp

这一行指定浮点单元的类型。softvfp 表示使用软件浮点运算，适用于没有硬件浮点单元的环境。Cortex-M4 也可以配备硬件浮点单元，但这里选择的是软件实现。

.thumb

这一指令表明接下来将使用 Thumb 指令集。Thumb 是一种精简的指令集，旨在提高性能和降低代码尺寸，特别适合资源受限的嵌入式系统。

.global g_pfnVectors

这条指令声明 g_pfnVectors 为全局符号，意味着它可以被其他模块或文件引用。通常，这个符号会指向中断向量表的起始地址。

.global Default_Handler

类似于上一条，声明 Default_Handler 为全局符号。这个符号通常是一个默认的中断处理函数，当未定义具体中断处理程序时，系统会调用此函数。

/* start address for the initialization values of the .data section. defined in linker script */
.word _sidata

这一行的意思是将 _sidata 符号的值（也就是 .data 段的初始数据的起始地址）存储为一个字（32 位）的数据。这个值将在程序启动时用于初始化 RAM 中的 .data 段，以确保静态和全局变量能够得到正确的初始值。

.word 

在汇编语言中，.word 是一个伪指令（pseudo-instruction），用于定义一个或多个字（通常是 32 位）数据的存储空间。它的主要作用是：

• 含义
  存储数据：使用 .word 可以将一个数值（常量）放入输出文件的特定位置。例如，如果写 0x12345678，那么这条指令将把这个 32 位的数字存储到指定的内存地址。

占用空间：除了存储具体的数值外，.word 还会在程序计数器（PC）指向的地方占用相应的内存空间。在 ARM 架构中，一个字通常是 4 个字节（32 位）。

• 示例
  例如：

.word 0x00000001
.word 0x00000002

这段代码会在内存中依次存储两个 32 位的字，分别为 0x00000001 和 0x00000002。

ldr r3, [r3, r1]

Arm®v7-M Architecture Reference Manual 文档有讲解。

具体含义是从 Flash 中读取数据段初始化值，存储在 r1 偏移位置。

.section .text.Reset_Handler

定义一个名为 Reset_Handler 的代码节（section），该节包含重置处理程序的代码。
.weak Reset_Handler

声明 Reset_Handler 为弱符号（weak symbol）。如果其他模块定义了同名的强符号，则链接时会使用强符号；否则，使用这个弱符号。
.type Reset_Handler, %function

指定 Reset_Handler 的类型为函数。
Reset_Handler:

定义 Reset_Handler 标签，表示该位置是重置处理程序的起始位置。
ldr sp, =_estack

将 _estack 的地址加载到堆栈指针（SP）寄存器中，设置堆栈的起始位置。

数据段初始化
movs r1, #0

将寄存器 r1 清零，用于后续的数据段初始化计数。
b LoopCopyDataInit

跳转到 LoopCopyDataInit，开始数据段初始化的循环。
CopyDataInit:

数据段初始化标签，下面是从 Flash 复制数据到 SRAM 的具体实现。
ldr r3, =_sidata

加载 _sidata（数据段初始化器的起始地址）到寄存器 r3。
ldr r3, [r3, r1]

从 Flash 中读取数据段初始化值，存储在 r1 偏移位置。
str r3, [r0, r1]

将读取的值存储到 SRAM 中。
adds r1, r1, #4

增加 r1 的值，移动到下一个数据元素（每个元素 4 字节）。
继续数据段初始化循环
LoopCopyDataInit:

循环标签，继续数据复制过程。
ldr r0, =_sdata

加载 .data 段的起始地址到 r0。
ldr r3, =_edata

加载 .data 段的结束地址到 r3。
adds r2, r0, r1

计算当前 SRAM 地址。
cmp r2, r3

比较当前地址与结束地址。
bcc CopyDataInit

如果未到达结束地址，则跳转回 CopyDataInit 开始下一个数据的复制。
初始化 BSS 段
ldr r2, =_sbss

加载 BSS 段的起始地址。
b LoopFillZerobss

跳转到填充 BSS 段的循环。
FillZerobss:

BSS 段填充标签，将 BSS 段初始化为零。
movs r3, #0

将 r3 清零。
str r3, [r2], #4

将零写入 BSS 段，并将指针向后移动四个字节。
LoopFillZerobss:

循环标签，继续填充 BSS 段的过程。
ldr r3, = _ebss

加载 BSS 段的结束地址。
cmp r2, r3

比较当前地址与结束地址。
bcc FillZerobss

如果未到达结束地址，则跳回填充操作。
系统初始化和应用入口
bl SystemInit

调用系统初始化函数，用于设置时钟系统或其他硬件配置。
bl entry

调用应用程序的入口点，\

这段代码是 Cortex-M 微控制器的启动代码的一部分，主要包括重置处理程序、默认中断处理程序以及中断向量表的定义。下面是逐行解析：

重置处理程序的后续部分
bl SystemInit

调用系统初始化函数 SystemInit，通常用于配置时钟设置和其他硬件初始状态。
/* Call static constructors */

注释掉的部分，指的是调用静态构造函数（C++），如果需要的话，使用 __libc_init_array 来初始化静态对象。
bl entry

调用应用程序的入口点 entry，程序从这里开始执行用户代码。
bx lr

返回到链接寄存器（LR）所指向的地址。这个指令在正常情况下不应该被执行，因为程序已经跳转到了用户代码。
.size Reset_Handler, .-Reset_Handler

定义 Reset_Handler 的大小，计算其结束位置与开始位置之间的字节数。
默认中断处理程序
/* This is the code that gets called when the processor receives an unexpected interrupt. */

该注释描述了默认的中断处理程序，当处理器接收到意外中断时将调用此处理程序。
.section .text.Default_Handler,“ax”,%progbits

定义一个名为 Default_Handler 的代码节，用于存放默认中断处理程序。
Default_Handler:

定义 Default_Handler 标签，表示这是默认中断处理程序的起始位置。
Infinite_Loop:

无限循环标签，进入此循环后不会返回，保持系统状态以便调试。
b Infinite_Loop

跳转到 Infinite_Loop，实现无限循环。这种设计确保当发生未处理的中断时，系统不会崩溃，而是保持在安全的状态，可以通过调试工具检查。
.size Default_Handler, .-Default_Handler

定义 Default_Handler 的大小。
中断向量表
/*****************************************************************************/

注释，说明以下是 Cortex-M3 的最小中断向量表。
.section .isr_vector,“a”,%progbits

定义中断向量表的节，使用 .isr_vector 名称，并指定相关属性。
.type g_pfnVectors, %object

指定 g_pfnVectors 的类型为对象。
.size g_pfnVectors, .-g_pfnVectors

定义中断向量表的大小。
g_pfnVectors:

定义中断向量表的标签。
.word _estack

将 _estack 的值放入向量表的第一个条目，表示堆栈的顶端地址。这是处理器复位或中断时使用的初始堆栈指针。
.word Reset_Handler

将 Reset_Handler 的地址放入向量表的第二个条目，表示复位处理中调用的函数。
.word NMI_Handler

将 NMI_Handler 的地址放入向量表的下一个条目，表示非屏蔽中断的处理函数。这个函数通常需要在用户代码中实现。