文件开头是关于文件的描述，先粘过来后面解释：
代码语言：javascript复制/**
******************************************************************************
* @file startup_stm32f407xx.s
* @author MCD Application Team
* @brief STM32F407xx 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>© 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.
*
******************************************************************************
*/开头部分描述了文件的用途及版权声明：基于GCC编译链的STM32F407xx设备中断向量表，主要描述了
- 初始SP，PC寄存器的初始值。
- PC的初始值即
Reset_Handler - 设置中断向量表入口地址，并用异常地址初始化向量表。 向量表里面保存的是异常响应的时候服务例程的入口地址。STM32把向量表放在0地址开始的code区。
- 转到C库的
__main（最后调用mian()） - 复位CortexM4之后，处理器处于线程模式，特权优先级。
定义
继续往下看
代码语言：javascript复制 .syntax unified
.cpu cortex-m4
.fpu softvfp
.thumb
.global g_pfnVectors
.global Default_Handler.syntax unified是一个指示，默认值divided（分裂的） 旧样式，下面的指令使用ARM和THUMB各自独立的语法。unified （统一的）新样式，下面的指令使用ARM和THUMB通用格式。.cpu表示后面用到的CPU平台为cortex-M4.fpu表示后面使用的是软浮点，软浮点即Soft-float，浮点单元即VFP，(vector floating-point)，相关资料可据此查询.thumb使用thumb模式等价于.code 16;gcc -mthumb.global定义了全局符号（symbol），.global使该符号对.ld（连接文件）可见。g_pfnVectors即中断向量表，Default_Handler我们这里先不解释，后面再看
