前言

这里以stm32f103为硬件平台,搭建了stm32f1系列的标准库,版本是V3.5,在路径标准库的源码路径下Libraries\CMSIS\CM3\DeviceSupport\ST\STM32F10x\startup包含了各个编译器或者说IDE的启动文件: 这些IDE分别是armgcc_ride7,iar,TrueSTUDIO,不过这不是关注的重点,本文主要分析startup_stm32f10x_md.s

分析startup_stm32f10x_md.s

首先看一下arm文件夹下的文件,具体如下;

-ar---        2011/3/10     10:52          15766 startup_stm32f10x_cl.s
-ar---        2011/3/10     10:52          15503 startup_stm32f10x_hd.s
-ar---        2011/3/10     10:52          15692 startup_stm32f10x_hd_vl.s
-ar---        2011/3/10     10:52          12376 startup_stm32f10x_ld.s
-ar---        2011/3/10     10:52          13656 startup_stm32f10x_ld_vl.s
-ar---        2011/3/10     10:52          12765 startup_stm32f10x_md.s
-ar---        2011/3/10     10:51          14073 startup_stm32f10x_md_vl.s
-ar---        2011/3/10     10:51          15955 startup_stm32f10x_xl.s

这里可以看到文件最终加以区分的是xl,md_vl,md等等,这些需要根据芯片具体的容量不同进行选择; 下面看一下startup_stm32f10x_md.s的汇编代码另外一般用户的代码都是从main()函数开始的,但是在此之前,则有启动代码初始化化硬件环境,然后跳转到 c runtime lib__main中,进行运行环境的初始化,包括栈,堆等等,最终跳转到用户的main函数中。这里没有找到c runtime lib的源码,着实有点遗憾。

在分析源码之前,有必要对部分汇编指令进行简单的了解,这里参考了《Cortex_M3权威指南》

汇编指令

EQU

将一个变量赋值,例如:Stack_Size EQU 0x00000400|

AREA

用于定义一个代码段或数据段,具体用法如:AREA 段名称 {,参数1} {,参数2}...

SPACE

用于申请一片内存空间但不赋初值,例如:Stack_Mem SPACE 0x00000400,分配1024字节的内存控制,感觉相当于mallocStack_Mem应该会该内存空间的首地址;

DCD

用于分配一片连续的字存储单元并用伪指令中指定的表达式初始化

PROC

该伪指令用于定义子程序,位置在子程序的开始处,它和ENDP分别表示子程序定义的开始和结束两者必须成对出现;

LDR

从存储器中加载字到一个寄存器中,Load Data to Register

常见的转移指令

  • B Label 跳转到 Label 处对应的地址
  • BX reg 跳转到由寄存器 reg 给出的地址
  • BL Label 跳转到 Label 对应的地址,并且把跳转前的下条指令地址保存到 LR
  • BLX reg 跳转到由寄存器 reg 给出的地址,并根据 REG 的 LSB 切换处理器状态,还要把转移前的下条指令地址保存到 LR

    LR(Link Register),连接寄存器的英文缩写,在ARM体系结构中LR的特殊用途有两种: 一是用来保存子程序返回地址; 二是当异常发生时,LR中保存的值等于异常发生时PC的值减4(或者减2),因此在各种异常模式下可以根据LR的值返回到异常发生前的相应位置继续执行。

源码分析

下面参考一下startup_stm32f10x_md.s的源码,进行分析一下。

;******************** (C) COPYRIGHT 2011 STMicroelectronics ********************
;* File Name          : startup_stm32f10x_md.s
;* Author             : MCD Application Team
;* Version            : V3.5.0
;* Date               : 11-March-2011
;* Description        : STM32F10x Medium Density 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
;*                      - Configure the clock system
;*                      - Branches to __main in the C library (which eventually
;*                        calls main()).
;*                      After Reset the CortexM3 processor is in Thread mode,
;*                      priority is Privileged, and the Stack is set to Main.
;* <<< Use Configuration Wizard in Context Menu >>>   
;*******************************************************************************
; THE PRESENT FIRMWARE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS
; WITH CODING INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME.
; AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT,
; INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE
; CONTENT OF SUCH FIRMWARE AND/OR THE USE MADE BY CUSTOMERS OF THE CODING
; INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.
;*******************************************************************************

; 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     0x00000400  ;栈空间 1024 Bytes1K的空间

                ;分配数据段,命名为`STACK`,数据段未初始化,可以读写
                AREA    STACK, NOINIT, READWRITE, ALIGN=3   ;
Stack_Mem       SPACE   Stack_Size
__initial_sp


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

Heap_Size       EQU     0x00000200  ;堆空间的配置,512 字节的空间

                AREA    HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem        SPACE   Heap_Size   ;分配堆空间为 512字节
__heap_limit

                PRESERVE8
                THUMB

; Vector Table Mapped to Address 0 at Reset
;向量表映射到地址0x00000000
                AREA    RESET, DATA, READONLY
                EXPORT  __Vectors       ;导出__Vectors符号,用于外部文件的使用
                EXPORT  __Vectors_End   ;导出向量表的结束地址
                EXPORT  __Vectors_Size  ;导出向量表的大小

;使用DCD__initial_sp以及异常地址分配内存空间,存到向量表中
__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     PendSV_Handler             ; PendSV Handler
                DCD     SysTick_Handler            ; SysTick Handler

                ; External Interrupts
                ; 外设的中断地址
                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_2
                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
__Vectors_End

__Vectors_Size  EQU  __Vectors_End - __Vectors  ;   计算向量表大小

                AREA    |.text|, CODE, READONLY ;   分配代码段,只读

; Reset handler
Reset_Handler    PROC
                 EXPORT  Reset_Handler             [WEAK]
     IMPORT  __main
     IMPORT  SystemInit
                 LDR     R0, =SystemInit
                 BLX     R0
                 LDR     R0, =__main
                 BX      R0
                 ENDP

; Dummy Exception Handlers (infinite loops which can be modified)
; [WEAK]指令会优先使用外部的链接符号,但是没有原型,编译器也不会出现报错
NMI_Handler     PROC
                EXPORT  NMI_Handler                [WEAK]
                B       .
                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
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  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]

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

                B       .

                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 2011 STMicroelectronics *****END OF FILE*****

主要做了这几个事情:

  1. 初始化堆栈内存空间;
  2. 设置PC寄存器的地址指向Reset_Handler,即上电便运行复位程序;
  3. 设置向量表,中断服务程序入口地址;
  4. 配置系统时钟, SystemInitmain函数运行前就已经运行了;
  5. 运行外部的函数,LDR R0, =__main,将__main地址装载到R0寄存器并运行,__main在C库中,会初始化程序的C运行环境,最终调用用户的main函数;