STM32单片机Bootloader设计（上）

原创乐创客 2021-07-14 07:05

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文 / Edward

STM32的启动文件

STM32作为一款单片机，它的启动方式很简单，即当Boot配置了从内部Flash启动模式之后，一上电程序就会从0x8000000地址处开始执行文件，因此我们在使用Keil设置程序起始地址的时候，需要将这个Flash地址设置成0x8000000，只有将这个地址设置成0x8000000，生成的hex文件才可以被正常烧录到此地址，单片机上电之后才可以正常启动。而如果使用J-Flash工具烧写Hex文件时，这个地址会自动根据Hex文件解析出来。然而如果当你烧写二进制Bin文件时，还需要手动将单片机的起始地址制定出来，关于Hex文件和Bin文件的异同点，这个又是可以长篇大论一番了，我们下次特别写文章来讲。

图1 Keil设置起始地址和空间

STM32启动文件

;********************* (C) COPYRIGHT 2017 STMicroelectronics ********************;* File Name          : startup_stm32l151xb.s;* Author             : MCD Application Team;* Description        : STM32L151XB Devices vector 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 system clock;*                      - Branches to __main in the C library (which eventually;*                        calls main()).;*                      After Reset the Cortex-M3 processor is in Thread mode,;*                      priority is Privileged, and the Stack is set to Main.;********************************************************************************;*;* Copyright (c) 2017 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;*;*******************************************************************************;* <<< Use Configuration Wizard in Context Menu >>>;; 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
                AREA    STACK, NOINIT, READWRITE, ALIGN=3Stack_Mem       SPACE   Stack_Size__initial_sp

; <h> Heap Configuration;   <o>  Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>; </h>
Heap_Size       EQU     0x00000200
                AREA    HEAP, NOINIT, READWRITE, ALIGN=3__heap_baseHeap_Mem        SPACE   Heap_Size__heap_limit
                PRESERVE8                THUMB

; 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     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                DCD     WWDG_IRQHandler           ; Window Watchdog                DCD     PVD_IRQHandler            ; PVD through EXTI Line detect                DCD     TAMPER_STAMP_IRQHandler   ; Tamper and Time Stamp                DCD     RTC_WKUP_IRQHandler       ; RTC Wakeup                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_IRQHandler           ; ADC1                DCD     USB_HP_IRQHandler         ; USB High Priority                DCD     USB_LP_IRQHandler         ; USB Low  Priority                DCD     DAC_IRQHandler            ; DAC                DCD     COMP_IRQHandler           ; COMP through EXTI Line                DCD     EXTI9_5_IRQHandler        ; EXTI Line 9..5                DCD     0                         ; Reserved                DCD     TIM9_IRQHandler           ; TIM9                DCD     TIM10_IRQHandler          ; TIM10                DCD     TIM11_IRQHandler          ; TIM11                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     RTC_Alarm_IRQHandler      ; RTC Alarm through EXTI Line                DCD     USB_FS_WKUP_IRQHandler    ; USB FS Wakeup from suspend                DCD     TIM6_IRQHandler           ; TIM6                DCD     TIM7_IRQHandler           ; TIM7                __Vectors_End
__Vectors_Size  EQU  __Vectors_End - __Vectors
                AREA    |.text|, CODE, READONLY
; Reset handler routineReset_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)
NMI_Handler     PROC                EXPORT  NMI_Handler                [WEAK]                B       .                ENDPHardFault_Handler\                PROC                EXPORT  HardFault_Handler          [WEAK]                B       .                ENDPMemManage_Handler\                PROC                EXPORT  MemManage_Handler          [WEAK]                B       .                ENDPBusFault_Handler\                PROC                EXPORT  BusFault_Handler           [WEAK]                B       .                ENDPUsageFault_Handler\                PROC                EXPORT  UsageFault_Handler         [WEAK]                B       .                ENDPSVC_Handler     PROC                EXPORT  SVC_Handler                [WEAK]                B       .                ENDPDebugMon_Handler\                PROC                EXPORT  DebugMon_Handler           [WEAK]                B       .                ENDPPendSV_Handler  PROC                EXPORT  PendSV_Handler             [WEAK]                B       .                ENDPSysTick_Handler PROC                EXPORT  SysTick_Handler            [WEAK]                B       .                ENDP
Default_Handler PROC
                EXPORT  WWDG_IRQHandler            [WEAK]                EXPORT  PVD_IRQHandler             [WEAK]                EXPORT  TAMPER_STAMP_IRQHandler    [WEAK]                EXPORT  RTC_WKUP_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_IRQHandler            [WEAK]                EXPORT  USB_HP_IRQHandler          [WEAK]                EXPORT  USB_LP_IRQHandler          [WEAK]                EXPORT  DAC_IRQHandler             [WEAK]                EXPORT  COMP_IRQHandler            [WEAK]                EXPORT  EXTI9_5_IRQHandler         [WEAK]                EXPORT  TIM9_IRQHandler            [WEAK]                EXPORT  TIM10_IRQHandler           [WEAK]                EXPORT  TIM11_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  RTC_Alarm_IRQHandler       [WEAK]                EXPORT  USB_FS_WKUP_IRQHandler     [WEAK]                EXPORT  TIM6_IRQHandler            [WEAK]                EXPORT  TIM7_IRQHandler            [WEAK]
WWDG_IRQHandlerPVD_IRQHandlerTAMPER_STAMP_IRQHandlerRTC_WKUP_IRQHandlerFLASH_IRQHandlerRCC_IRQHandlerEXTI0_IRQHandlerEXTI1_IRQHandlerEXTI2_IRQHandlerEXTI3_IRQHandlerEXTI4_IRQHandlerDMA1_Channel1_IRQHandlerDMA1_Channel2_IRQHandlerDMA1_Channel3_IRQHandlerDMA1_Channel4_IRQHandlerDMA1_Channel5_IRQHandlerDMA1_Channel6_IRQHandlerDMA1_Channel7_IRQHandlerADC1_IRQHandlerUSB_HP_IRQHandlerUSB_LP_IRQHandlerDAC_IRQHandlerCOMP_IRQHandlerEXTI9_5_IRQHandlerTIM9_IRQHandlerTIM10_IRQHandlerTIM11_IRQHandlerTIM2_IRQHandlerTIM3_IRQHandlerTIM4_IRQHandlerI2C1_EV_IRQHandlerI2C1_ER_IRQHandlerI2C2_EV_IRQHandlerI2C2_ER_IRQHandlerSPI1_IRQHandlerSPI2_IRQHandlerUSART1_IRQHandlerUSART2_IRQHandlerUSART3_IRQHandlerEXTI15_10_IRQHandlerRTC_Alarm_IRQHandlerUSB_FS_WKUP_IRQHandlerTIM6_IRQHandlerTIM7_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 STMicroelectronics *****END OF FILE*****

首先让我们来看下STM32启动文件，当MCU上电复位之后，整个程序会跳转到以0x8000000为基址，偏移0的地址处，即还是0x8000000。但是STM32的0x8000000地址处存放的并不是整个芯片的第一句指令，而是整个芯片的堆栈初始化程序，如图2所示。

图2 0x8000000偏移0地址处的堆栈初始化程序指针

由于STM32的地址空间都是4字节对齐的，因此这个栈顶指针的存放空间为4字节，所以STM32复位之后跳转的地址应该是0x8000000基址偏移4个字节，即0x8000004。如同3所示。

图3 STM32复位跳转地址

图3中的程序非常浅显易懂，第136和137行，即将程序跳转到SystemInit处，这是个C语言函数，定义在“system_stm32l1xx.c”文件里，它的目的就是对中断向量表起始地址进行指定，也就是图2中的“__Vector”处。当然CM3内核和CM0内核关于SCB（系统控制块）的定义有些许差别，CM0不在本文讨论中，但是CM3和CM4的中断向量表映射机制还是很相似的。

图4 SystemInit函数映射中断向量表

图4中我们可以看到，SCB中关于Vector的地址是通过符号FLASH_BASE和VECT_TAB_OFFSET计算出来的，我们可以找到关于它们的定义，如图5所示。

图5 FLASH_BASE和VECT_TAB_OFFSET的定义

通过图5中的计算，正好可以得出整个中断向量表被映射到了0x8000000地址处。

STM32的FLASH分配

前面的大段文章内容中，频繁提及了一个关键的数值，即0x8000000，那么这个0x8000000到底是怎么来的呢？这个数值并不是平白无故拍脑袋想出来的。之前我们就说过，ARM体系的存储器结构是其一大特色，而这个0x8000000正是整个STM32内置FLASH的起始地址。我们随便打开一份STM32的数据手册，在存储器章节里面就可以看到STM32全部的存储器定义。如图6所示。

图6 STM32内部FLASH的起始地址

STM32的Bootloader思路

抛开所有的Bootloader高级功能来说，我们设计STM32 Bootloader的主要目的有两个，第一个为方便程序烧写和更新，第二个目前是从Bootloader程序中跳转（引导）用户的应用程序。这两个目的中，对于Bootloader来说程序跳转尤其重要，因为程序跳转成不成功将会严重影响整个用户程序的运行状态。因而，怎么跳，何时跳，跳到哪里，则是下篇文章的着重讨论部分。

前面一个FLASH烧写，可以根据自己的特殊要求来定制，只要严格安装HEX文件指定的地址和数据的关系，一般不会出错。

本文分析了STM32启动时比较重要的一些定义和函数跳转，下篇将会开始着手设计一个STM32 Bootloader。