中容量STM32处理器启动代码的理解

本文主要是介绍中容量STM32处理器启动代码的理解，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

上个星期还看到ARM被日本软银给收购了，由此大家都很熟悉的ARM变成了一家日资企业，祝愿它能更好的发展~

今天要介绍一下STM32的启动代码，我这里使用的是中容量的STM32f103c8t6,对应的启动文件就是startup_stm32f10x_md.s，我这里启动文件版本是V3.6.2

不多说废话，先上我注释过的源码：

/********************************************************************************* @file      startup_stm32f10x_md.s* @author    MCD Application Team* @version   V3.6.2* @date      28-February-2013* @brief     STM32F10x Medium Density Devices vector table for RIDE7 toolchain.*            This module performs:*                - Set the initial SP                                              -设置最初的SP寄存器值*                - Set the initial PC == Reset_Handler,							 -设置最初的PC寄存器值 == Reset_Handler*                - Set the vector table entries with the exceptions ISR address    -在有特殊的ISR(中断服务程序)地址的情况下设置向量表入口*                - Configure the clock system 									 -设置时钟系统*                - Branches to main in the C library (which eventually			 -C库文件中由分支到主函数（最后调用了主函数）*                  calls main()).*            After Reset the Cortex-M3 processor is in Thread mode,				 在线程模式下复位了CM3处理器后，此时优先级特权化，栈顶设置为主函数*            priority is Privileged, and the Stack is set to Main.******************************************************************************* @attention** <h2><center>&copy; COPYRIGHT 2013 STMicroelectronics</center></h2>** Licensed under MCD-ST Liberty SW License Agreement V2, (the "License");* You may not use this file except in compliance with the License.* You may obtain a copy of the License at:**        http://www.st.com/software_license_agreement_liberty_v2** Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.********************************************************************************/.syntax unified                                                                   ;表示使用了统一汇编语言语法.cpu cortex-m3                                                                  ;MCU为CM3.fpu softvfp.thumb                                                                          ;指令集.global	g_pfnVectors                                                                ;global使得g_pfnVectors可以被其他目标文件使用
.global	Default_Handler/* start address for the initialization values of the .data section.                初始化.data 块的起始地址，这个地址在链接脚本中被定义
defined in linker script */
.word	_sidata
/* start address for the .data section. defined in linker script                    .data块的起始地址，这个地址在链接脚本中被定义*/  
.word	_sdata
/* end address for the .data section. defined in linker script                      .data块的结束地址，这个地址在链接脚本中被定义*/
.word	_edata
/* start address for the .bss section. defined in linker script                     .bss块的起始地址，这个地址在链接脚本中被定义*/
.word	_sbss
/* end address for the .bss section. defined in linker script                       .bss块的结束地址，这个地址在链接脚本中被定义*/
.word	_ebss.equ  BootRAM, 0xF108F85F                                                           /*这里跟c中的宏定义类似，即BootRAM = 0xF108F85F,不参与编译*/
/*** @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:	/* Copy the data segment initializers from flash to SRAM                             将初始化了的数据段从flash复制到SRAM*/  movs	r1, #0                                                                       ;将立即数0赋值给r1寄存器b	LoopCopyDataInit                                                                 ;程序转移到LoopCopyDataInit处CopyDataInit:                                                                        ;从FLASH中拷贝地址在sdata和edata之间的代码到SRAM中ldr	r3, =_sidata                                                                 ;从存储器中将_sidata加载到寄存器r3中ldr	r3, [r3, r1]                                                                 ;从地址r3+r1处读取一个字（32bit）到r3中str	r3, [r0, r1]                                                                 ;把寄存器r3的值存储到存储器中地址为r0+r1地址处adds	r1, r1, #4                                                               ;r1 = r1 + 4LoopCopyDataInit:ldr	r0, =_sdata                                                                  ;从存储器中将_sidata加载到寄存器r0中ldr	r3, =_edata                                                                  ;从存储器中将_edata加载到寄存器r3中adds	r2, r0, r1                                                               ;r2=r0+r1cmp	r2, r3                                                                       ;计算r2 - r3,若小于0，标志位为0，反之为1bcc	CopyDataInit                                                                 ;如果标志位为0（无借位）即r2<r3，则跳转到CopyDataInit处ldr	r2, =_sbss                                                                   ;从存储器中将_sbss加载到寄存器r2中b	LoopFillZerobss                                                              ;无条件跳转到LoopFillZerobss
/* Zero fill the bss segment. */  
FillZerobss:movs	r3, #0                                                                   ;将立即数0存入寄存器r3str	r3, [r2], #4                                                                 ;将寄存器r3的值存储到地址为r2寄存器值得地址处后，r2 = r2 + 4LoopFillZerobss:ldr	r3, = _ebss                                                                  ;从存储器中将_ebss加载到寄存器r3中cmp	r2, r3                                                                       ;比较r2,r3，然后更新标志位bcc	FillZerobss                                                                  ;如果标志位为0（无借位），则跳转到FillZerobss处
/* Call the clock system intitialization function.*/
/* bl  SystemInit */
/* Call the application's entry point.*/bl	main                                                                         ;转移到main函数起始处bx	lr                                                                           ;转移到地址lr处
.size	Reset_Handler, .-Reset_Handler                                               ;相当于mov pc lr    lr即寄存器r14/*** @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                                                                ;无条件跳转到Infinite_Loop.size	Default_Handler, .-Default_Handler
/******************************************************************************
*
* The minimal vector table for a Cortex M3.  Note that the proper constructs         Cortex M3的最小向量表
* must be placed on this to ensure that it ends up at physical address
* 0x0000.0000.
*
******************************************************************************/    .section	.isr_vector,"a",%progbits                                            ;定义中断向量表的数据段.type	g_pfnVectors, %object.size	g_pfnVectors, .-g_pfnVectorsg_pfnVectors:.word	_estack                                                                  ;在当前位置放置一个word型的值，这个值为_estack；后面同理.word	Reset_Handler                                                            ;这一块程序的意思就是说以g_pfnVectors为初始地址，然后依次.word	NMI_Handler                                                              ;以字为单位写入相应的数据.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.word	WWDG_IRQHandler.word	PVD_IRQHandler.word	TAMPER_IRQHandler.word	RTC_IRQHandler.word	FLASH_IRQHandler.word	RCC_IRQHandler.word	EXTI0_IRQHandler.word	EXTI1_IRQHandler.word	EXTI2_IRQHandler.word	EXTI3_IRQHandler.word	EXTI4_IRQHandler.word	DMA1_Channel1_IRQHandler.word	DMA1_Channel2_IRQHandler.word	DMA1_Channel3_IRQHandler.word	DMA1_Channel4_IRQHandler.word	DMA1_Channel5_IRQHandler.word	DMA1_Channel6_IRQHandler.word	DMA1_Channel7_IRQHandler.word	ADC1_2_IRQHandler.word	USB_HP_CAN1_TX_IRQHandler.word	USB_LP_CAN1_RX0_IRQHandler.word	CAN1_RX1_IRQHandler.word	CAN1_SCE_IRQHandler.word	EXTI9_5_IRQHandler.word	TIM1_BRK_IRQHandler.word	TIM1_UP_IRQHandler.word	TIM1_TRG_COM_IRQHandler.word	TIM1_CC_IRQHandler.word	TIM2_IRQHandler.word	TIM3_IRQHandler.word	TIM4_IRQHandler.word	I2C1_EV_IRQHandler.word	I2C1_ER_IRQHandler.word	I2C2_EV_IRQHandler.word	I2C2_ER_IRQHandler.word	SPI1_IRQHandler.word	SPI2_IRQHandler.word	USART1_IRQHandler.word	USART2_IRQHandler.word	USART3_IRQHandler.word	EXTI15_10_IRQHandler.word	RTCAlarm_IRQHandler.word	USBWakeUp_IRQHandler	.word	0.word	0.word	0.word	0.word	0.word	0.word	0.word	BootRAM          /* @0x108. This is for boot in RAM mode for             这个是为stm32f10系列中容量系列设备的boot中的RAM模式准备的STM32F10x Medium Density devices. *//*******************************************************************************
*
* 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                                                                 ;定义一个弱别名NMI_Handler.thumb_set NMI_Handler,Default_Handler                                          ;如果这个不重写这个弱别名，那么默认执行Default_Handler，反之这执行重写过的NMI_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	TAMPER_IRQHandler.thumb_set TAMPER_IRQHandler,Default_Handler.weak	RTC_IRQHandler.thumb_set RTC_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_Channel1_IRQHandler.thumb_set DMA1_Channel1_IRQHandler,Default_Handler.weak	DMA1_Channel2_IRQHandler.thumb_set DMA1_Channel2_IRQHandler,Default_Handler.weak	DMA1_Channel3_IRQHandler.thumb_set DMA1_Channel3_IRQHandler,Default_Handler.weak	DMA1_Channel4_IRQHandler.thumb_set DMA1_Channel4_IRQHandler,Default_Handler.weak	DMA1_Channel5_IRQHandler.thumb_set DMA1_Channel5_IRQHandler,Default_Handler.weak	DMA1_Channel6_IRQHandler.thumb_set DMA1_Channel6_IRQHandler,Default_Handler.weak	DMA1_Channel7_IRQHandler.thumb_set DMA1_Channel7_IRQHandler,Default_Handler.weak	ADC1_2_IRQHandler.thumb_set ADC1_2_IRQHandler,Default_Handler.weak	USB_HP_CAN1_TX_IRQHandler.thumb_set USB_HP_CAN1_TX_IRQHandler,Default_Handler.weak	USB_LP_CAN1_RX0_IRQHandler.thumb_set USB_LP_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_IRQHandler.thumb_set TIM1_BRK_IRQHandler,Default_Handler.weak	TIM1_UP_IRQHandler.thumb_set TIM1_UP_IRQHandler,Default_Handler.weak	TIM1_TRG_COM_IRQHandler.thumb_set TIM1_TRG_COM_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	RTCAlarm_IRQHandler.thumb_set RTCAlarm_IRQHandler,Default_Handler.weak	USBWakeUp_IRQHandler.thumb_set USBWakeUp_IRQHandler,Default_Handler/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

如果有注释不准确的地方还希望能够给我指出，感谢感谢~~

这里以STM32程序运行过程为轴线，依次介绍单片机启动过程中的流程。

在给单片机上电前，先通过给BOOT0和BOOT1连接高低电平来设置程序启动的初始位置。STM32程序启动的位置有三种：

1：Main Flash memory

是STM32内置的Flash，一般我们使用JTAG或者SWD模式下载程序时，就是下载到这个里面，重启后也直接从这启动程序。

2：System memory

从系统存储器启动，这种模式启动的程序功能是由厂家设置的。一般来说，这种启动方式用的比较少。

3：Embedded Memory

内置SRAM，既然是SRAM，自然也就没有程序存储的能力了，这个模式一般用于程序调试。

在这三种方式里面用的最多的是第一种，下面以第一种启动方式为例进行介绍：

在重启芯片时，SYSCLK的第4个上升沿，BOOT引脚的值将被锁存。然后进入启动文件，具体的启动文件为startup_stm32f10x_md.s。

首先启动文件中有一个Reset_Handler，这个汇编函数的作用有两个：