STM32的啟動文件

STM32作為一款單片機，它的啟動方式很簡單，即當Boot配置了從內部Flash啟動模式之后，一上電程序就會從0x8000000地址處開始執行文件，因此我們在使用Keil設置程序起始地址的時候，需要將這個Flash地址設置成0x8000000，只有將這個地址設置成0x8000000，生成的hex文件才可以被正常燒錄到此地址，單片機上電之后才可以正常啟動。而如果使用J-Flash工具燒寫Hex文件時，這個地址會自動根據Hex文件解析出來。然而如果當你燒寫二進制Bin文件時，還需要手動將單片機的起始地址制定出來，關于Hex文件和Bin文件的異同點，這個又是可以長篇大論一番了，我們下次特別寫文章來講。

圖1 Keil設置起始地址和空間

STM32啟動文件

;********************* (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=3
Stack_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_base
Heap_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 routine
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)


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_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_IRQHandler
PVD_IRQHandler
TAMPER_STAMP_IRQHandler
RTC_WKUP_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_IRQHandler
USB_HP_IRQHandler
USB_LP_IRQHandler
DAC_IRQHandler
COMP_IRQHandler
EXTI9_5_IRQHandler
TIM9_IRQHandler
TIM10_IRQHandler
TIM11_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
RTC_Alarm_IRQHandler
USB_FS_WKUP_IRQHandler
TIM6_IRQHandler
TIM7_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*****

首先讓我們來看下STM32啟動文件，當MCU上電復位之后，整個程序會跳轉到以0x8000000為基址，偏移0的地址處，即還是0x8000000。但是STM32的0x8000000地址處存放的并不是整個芯片的第一句指令，而是整個芯片的堆棧初始化程序，如圖2所示。

圖2 0x8000000偏移0地址處的堆棧初始化程序指針

由于STM32的地址空間都是4字節對齊的，因此這個棧頂指針的存放空間為4字節，所以STM32復位之后跳轉的地址應該是0x8000000基址偏移4個字節，即0x8000004。如同3所示。

圖3 STM32復位跳轉地址

圖3中的程序非常淺顯易懂，第136和137行，即將程序跳轉到SystemInit處，這是個C語言函數，定義在“system_stm32l1xx.c”文件里，它的目的就是對中斷向量表起始地址進行指定，也就是圖2中的“__Vector”處。當然CM3內核和CM0內核關于SCB（系統控制塊）的定義有些許差別，CM0不在本文討論中，但是CM3和CM4的中斷向量表映射機制還是很相似的。

圖4 SystemInit函數映射中斷向量表

圖4中我們可以看到，SCB中關于Vector的地址是通過符號FLASH_BASE和VECT_TAB_OFFSET計算出來的，我們可以找到關于它們的定義，如圖5所示。

圖5 FLASH_BASE和VECT_TAB_OFFSET的定義

通過圖5中的計算，正好可以得出整個中斷向量表被映射到了0x8000000地址處。

STM32的FLASH分配

前面的大段文章內容中，頻繁提及了一個關鍵的數值，即0x8000000，那么這個0x8000000到底是怎么來的呢？這個數值并不是平白無故拍腦袋想出來的。之前我們就說過，ARM體系的存儲器結構是其一大特色，而這個0x8000000正是整個STM32內置FLASH的起始地址。我們隨便打開一份STM32的數據手冊，在存儲器章節里面就可以看到STM32全部的存儲器定義。如圖6所示。

圖6 STM32內部FLASH的起始地址

STM32的Bootloader思路

拋開所有的Bootloader高級功能來說，我們設計STM32 Bootloader的主要目的有兩個，第一個為方便程序燒寫和更新，第二個目前是從Bootloader程序中跳轉（引導）用戶的應用程序。這兩個目的中，對于Bootloader來說程序跳轉尤其重要，因為程序跳轉成不成功將會嚴重影響整個用戶程序的運行狀態。因而，怎么跳，何時跳，跳到哪里，則是下篇文章的著重討論部分。

前面一個FLASH燒寫，可以根據自己的特殊要求來定制，只要嚴格安裝HEX文件指定的地址和數據的關系，一般不會出錯。

本文分析了STM32啟動時比較重要的一些定義和函數跳轉，下篇將會開始著手設計一個STM32 Bootloader。