最近終於閑了下來了准備好好學習下Cortex-M3/M4系列處理器的架構,經過各種資料的折磨也沒法對它的整個工作過程能有個完整的認知,最后看到一片博客打算從程序的運行過程開始探究,所以首先就找到了啟動文件因為它可是你的程序開始跑之前的一些重要的准備工作,想要更好的使用某一款芯片了解程序在芯片內運行的始末就顯得十分重要了。就像一個博客中這么寫到:“每一款芯片的啟動文件都值得去研究,因為它可是你的程序跑的最初一段路,不可以不知道。通過了解啟動文件,我們可以體會到處理器的架構、指令集、中斷向量安排等內容,是非常值得玩味的”。
在開始之前先鋪墊一下,啟動文件里涉及到的匯編指令的用法
其中DCD 相當於C語言力的&,定義地址。
啟動文所做的操作主要有:
- 初始化棧
- 初始化堆
- 初始化中斷向量表
- 系統初始化
- 函數聲明
1,初始化棧
Stack_Size EQU 0x00000400 :0x00000400=1024 AREA STACK, NOINIT, READWRITE, ALIGN=3 Stack_Mem SPACE Stack_Size __initial_sp
其中第二行匯編了數據段STACK 其中 NOINIT 表示未初始化,READWRITE可讀可寫,ALLGN 2*3 = 8 八字節對齊,第三行為STACK分配了大小為1KB的內存空間,緊跟着后面的__initial_sp 因為其是緊跟着棧分配內存后所以其為棧頂(遞減棧)。最終__init_sp為1KB空間棧的棧頂,棧主要用於函數局部變量和形參的及調用過程的臨時存儲,屬於編譯器自動分配和釋放的內存,所以這里需要注意如果你的函數所占的內存大過這個空間應調整其大小但一定要小於內部SARM的大小。堆是程序員進行分配和釋放的,如果程序中未釋放最后由系統回收。
2,初始化堆
Heap_Size EQU 0x00000200 ;0x00000200 = 1000 AREA HEAP, NOINIT, READWRITE, ALIGN=3 __heap_base Heap_Mem SPACE Heap_Size __heap_limit PRESERVE8 THUMB
其中第二行匯編了一個數據段HEAP NOINIT 未初始化,READWRITE可讀可寫,ALLGN 2*3 = 8 八字節對齊,第三行定義堆的起始地址 __heap_base 接下來就按匯編的數據類型和大小分配堆的1000B內存同樣 __heap_limit就為堆的最后一個地址。對於內存可以看這個博客:http://blog.csdn.net/qq_29119171/article/details/53764823
PRESERVE8 編譯器指令8字節對齊
THUMB 選擇芯片的指令集到此堆初始化完成。
2,初始化中斷向量表

; 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 detection DCD TAMP_STAMP_IRQHandler ; Tamper and TimeStamps through the EXTI line DCD RTC_WKUP_IRQHandler ; RTC Wakeup through the EXTI line DCD FLASH_IRQHandler ; FLASH DCD RCC_IRQHandler ; RCC DCD EXTI0_IRQHandler ; EXTI Line0 DCD EXTI1_IRQHandler ; EXTI Line1 DCD EXTI2_IRQHandler ; EXTI Line2 DCD EXTI3_IRQHandler ; EXTI Line3 DCD EXTI4_IRQHandler ; EXTI Line4 DCD DMA1_Stream0_IRQHandler ; DMA1 Stream 0 DCD DMA1_Stream1_IRQHandler ; DMA1 Stream 1 DCD DMA1_Stream2_IRQHandler ; DMA1 Stream 2 DCD DMA1_Stream3_IRQHandler ; DMA1 Stream 3 DCD DMA1_Stream4_IRQHandler ; DMA1 Stream 4 DCD DMA1_Stream5_IRQHandler ; DMA1 Stream 5 DCD DMA1_Stream6_IRQHandler ; DMA1 Stream 6 DCD ADC_IRQHandler ; ADC1, ADC2 and ADC3s DCD CAN1_TX_IRQHandler ; CAN1 TX DCD CAN1_RX0_IRQHandler ; CAN1 RX0 DCD CAN1_RX1_IRQHandler ; CAN1 RX1 DCD CAN1_SCE_IRQHandler ; CAN1 SCE DCD EXTI9_5_IRQHandler ; External Line[9:5]s DCD TIM1_BRK_TIM9_IRQHandler ; TIM1 Break and TIM9 DCD TIM1_UP_TIM10_IRQHandler ; TIM1 Update and TIM10 DCD TIM1_TRG_COM_TIM11_IRQHandler ; TIM1 Trigger and Commutation and TIM11 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 ; External Line[15:10]s DCD RTC_Alarm_IRQHandler ; RTC Alarm (A and B) through EXTI Line DCD OTG_FS_WKUP_IRQHandler ; USB OTG FS Wakeup through EXTI line DCD TIM8_BRK_TIM12_IRQHandler ; TIM8 Break and TIM12 DCD TIM8_UP_TIM13_IRQHandler ; TIM8 Update and TIM13 DCD TIM8_TRG_COM_TIM14_IRQHandler ; TIM8 Trigger and Commutation and TIM14 DCD TIM8_CC_IRQHandler ; TIM8 Capture Compare DCD DMA1_Stream7_IRQHandler ; DMA1 Stream7 DCD FSMC_IRQHandler ; FSMC DCD SDIO_IRQHandler ; SDIO DCD TIM5_IRQHandler ; TIM5 DCD SPI3_IRQHandler ; SPI3 DCD UART4_IRQHandler ; UART4 DCD UART5_IRQHandler ; UART5 DCD TIM6_DAC_IRQHandler ; TIM6 and DAC1&2 underrun errors DCD TIM7_IRQHandler ; TIM7 DCD DMA2_Stream0_IRQHandler ; DMA2 Stream 0 DCD DMA2_Stream1_IRQHandler ; DMA2 Stream 1 DCD DMA2_Stream2_IRQHandler ; DMA2 Stream 2 DCD DMA2_Stream3_IRQHandler ; DMA2 Stream 3 DCD DMA2_Stream4_IRQHandler ; DMA2 Stream 4 DCD ETH_IRQHandler ; Ethernet DCD ETH_WKUP_IRQHandler ; Ethernet Wakeup through EXTI line DCD CAN2_TX_IRQHandler ; CAN2 TX DCD CAN2_RX0_IRQHandler ; CAN2 RX0 DCD CAN2_RX1_IRQHandler ; CAN2 RX1 DCD CAN2_SCE_IRQHandler ; CAN2 SCE DCD OTG_FS_IRQHandler ; USB OTG FS DCD DMA2_Stream5_IRQHandler ; DMA2 Stream 5 DCD DMA2_Stream6_IRQHandler ; DMA2 Stream 6 DCD DMA2_Stream7_IRQHandler ; DMA2 Stream 7 DCD USART6_IRQHandler ; USART6 DCD I2C3_EV_IRQHandler ; I2C3 event DCD I2C3_ER_IRQHandler ; I2C3 error DCD OTG_HS_EP1_OUT_IRQHandler ; USB OTG HS End Point 1 Out DCD OTG_HS_EP1_IN_IRQHandler ; USB OTG HS End Point 1 In DCD OTG_HS_WKUP_IRQHandler ; USB OTG HS Wakeup through EXTI DCD OTG_HS_IRQHandler ; USB OTG HS DCD DCMI_IRQHandler ; DCMI DCD CRYP_IRQHandler ; CRYP crypto DCD HASH_RNG_IRQHandler ; Hash and Rng DCD FPU_IRQHandler ; FPU __Vectors_End __Vectors_Size EQU __Vectors_End - __Vectors
這是一個中斷向量表,向量表從FLASH 的0x00000000 地址開始放置,以4 個字節為一個單位,地址0 存放的是棧頂(sp_init)地址,0X00000004 存放的是復位程序的地址,以此類推。從代碼上看,向量表中存放的都是中斷服務函數的函數名,可我們知道C 語言中的函數名就是一個地址。(由此知道,中斷函數的函數名都已經知道了)。 從那里對應地址取出服務例程的入口地址並跳入。要注意的是這里有個另類:0 號類型並不是什么入口地址,而是給出了復位后MSP 的初值。
3.系統初始化函數及中斷函數聲明

AREA |.text|, CODE, READONLY ; Reset handler Reset_Handler PROC EXPORT Reset_Handler [WEAK] IMPORT SystemInit IMPORT __main 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 TAMP_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_Stream0_IRQHandler [WEAK] EXPORT DMA1_Stream1_IRQHandler [WEAK] EXPORT DMA1_Stream2_IRQHandler [WEAK] EXPORT DMA1_Stream3_IRQHandler [WEAK] EXPORT DMA1_Stream4_IRQHandler [WEAK] EXPORT DMA1_Stream5_IRQHandler [WEAK] EXPORT DMA1_Stream6_IRQHandler [WEAK] EXPORT ADC_IRQHandler [WEAK] EXPORT CAN1_TX_IRQHandler [WEAK] EXPORT CAN1_RX0_IRQHandler [WEAK] EXPORT CAN1_RX1_IRQHandler [WEAK] EXPORT CAN1_SCE_IRQHandler [WEAK] EXPORT EXTI9_5_IRQHandler [WEAK] EXPORT TIM1_BRK_TIM9_IRQHandler [WEAK] EXPORT TIM1_UP_TIM10_IRQHandler [WEAK] EXPORT TIM1_TRG_COM_TIM11_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 RTC_Alarm_IRQHandler [WEAK] EXPORT OTG_FS_WKUP_IRQHandler [WEAK] EXPORT TIM8_BRK_TIM12_IRQHandler [WEAK] EXPORT TIM8_UP_TIM13_IRQHandler [WEAK] EXPORT TIM8_TRG_COM_TIM14_IRQHandler [WEAK] EXPORT TIM8_CC_IRQHandler [WEAK] EXPORT DMA1_Stream7_IRQHandler [WEAK] EXPORT FSMC_IRQHandler [WEAK] EXPORT SDIO_IRQHandler [WEAK] EXPORT TIM5_IRQHandler [WEAK] EXPORT SPI3_IRQHandler [WEAK] EXPORT UART4_IRQHandler [WEAK] EXPORT UART5_IRQHandler [WEAK] EXPORT TIM6_DAC_IRQHandler [WEAK] EXPORT TIM7_IRQHandler [WEAK] EXPORT DMA2_Stream0_IRQHandler [WEAK] EXPORT DMA2_Stream1_IRQHandler [WEAK] EXPORT DMA2_Stream2_IRQHandler [WEAK] EXPORT DMA2_Stream3_IRQHandler [WEAK] EXPORT DMA2_Stream4_IRQHandler [WEAK] EXPORT ETH_IRQHandler [WEAK] EXPORT ETH_WKUP_IRQHandler [WEAK] EXPORT CAN2_TX_IRQHandler [WEAK] EXPORT CAN2_RX0_IRQHandler [WEAK] EXPORT CAN2_RX1_IRQHandler [WEAK] EXPORT CAN2_SCE_IRQHandler [WEAK] EXPORT OTG_FS_IRQHandler [WEAK] EXPORT DMA2_Stream5_IRQHandler [WEAK] EXPORT DMA2_Stream6_IRQHandler [WEAK] EXPORT DMA2_Stream7_IRQHandler [WEAK] EXPORT USART6_IRQHandler [WEAK] EXPORT I2C3_EV_IRQHandler [WEAK] EXPORT I2C3_ER_IRQHandler [WEAK] EXPORT OTG_HS_EP1_OUT_IRQHandler [WEAK] EXPORT OTG_HS_EP1_IN_IRQHandler [WEAK] EXPORT OTG_HS_WKUP_IRQHandler [WEAK] EXPORT OTG_HS_IRQHandler [WEAK] EXPORT DCMI_IRQHandler [WEAK] EXPORT CRYP_IRQHandler [WEAK] EXPORT HASH_RNG_IRQHandler [WEAK] EXPORT FPU_IRQHandler [WEAK] //如下定義一個空函數 WWDG_IRQHandler PVD_IRQHandler TAMP_STAMP_IRQHandler RTC_WKUP_IRQHandler FLASH_IRQHandler RCC_IRQHandler EXTI0_IRQHandler EXTI1_IRQHandler EXTI2_IRQHandler EXTI3_IRQHandler EXTI4_IRQHandler DMA1_Stream0_IRQHandler DMA1_Stream1_IRQHandler DMA1_Stream2_IRQHandler DMA1_Stream3_IRQHandler DMA1_Stream4_IRQHandler DMA1_Stream5_IRQHandler DMA1_Stream6_IRQHandler ADC_IRQHandler CAN1_TX_IRQHandler CAN1_RX0_IRQHandler CAN1_RX1_IRQHandler CAN1_SCE_IRQHandler EXTI9_5_IRQHandler TIM1_BRK_TIM9_IRQHandler TIM1_UP_TIM10_IRQHandler TIM1_TRG_COM_TIM11_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 RTC_Alarm_IRQHandler OTG_FS_WKUP_IRQHandler TIM8_BRK_TIM12_IRQHandler TIM8_UP_TIM13_IRQHandler TIM8_TRG_COM_TIM14_IRQHandler TIM8_CC_IRQHandler DMA1_Stream7_IRQHandler FSMC_IRQHandler SDIO_IRQHandler TIM5_IRQHandler SPI3_IRQHandler UART4_IRQHandler UART5_IRQHandler TIM6_DAC_IRQHandler TIM7_IRQHandler DMA2_Stream0_IRQHandler DMA2_Stream1_IRQHandler DMA2_Stream2_IRQHandler DMA2_Stream3_IRQHandler DMA2_Stream4_IRQHandler ETH_IRQHandler ETH_WKUP_IRQHandler CAN2_TX_IRQHandler CAN2_RX0_IRQHandler CAN2_RX1_IRQHandler CAN2_SCE_IRQHandler OTG_FS_IRQHandler DMA2_Stream5_IRQHandler DMA2_Stream6_IRQHandler DMA2_Stream7_IRQHandler USART6_IRQHandler I2C3_EV_IRQHandler I2C3_ER_IRQHandler OTG_HS_EP1_OUT_IRQHandler OTG_HS_EP1_IN_IRQHandler OTG_HS_WKUP_IRQHandler OTG_HS_IRQHandler DCMI_IRQHandler CRYP_IRQHandler HASH_RNG_IRQHandler FPU_IRQHandler
AREA |.text|, CODE, READONLY定義一個名稱為.text 的代碼段,可讀程序段。
PROC與ENDP組合在匯編中定義一段子函數
類似與這種形式:EXPORT FPU_IRQHandler [WEAK]的用法,其中WEAK是弱定義的意思,如果外部定義了就先使用外部定義的內容,若未定義則會執行地下的空函數且返回到空函數(死循環)。
4.用戶堆棧的初始化
這以部分也就是把初始化的堆棧地址賦值給單片機的對應寄存器以方便C程序進行分配釋放使用。
User Stack and Heap initialization ;******************************************************************************* IF :DEF:__MICROLIB //這一部分是關於是否使用微庫 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
使用微庫與不使用微庫的區別(參考:http://www.cnblogs.com/amanlikethis/p/3719529.html)
使用微庫就意味着我們不想使用MDK提供的庫函數,而想用自己定義的庫函數,比如說printf函數。那么這一點是怎樣實現的呢?我們以printf函數為例進行說明。不使用微庫而使用系統庫在連接程序時,肯定會把系統中包含printf函數的庫拿來調用參與連接,即代碼段有系統庫的參與。在啟動過程中,不使用微庫而使用系統庫在初始化棧的時候,還需要初始化堆(猜測系統庫需要用到堆),而使用微庫則是不需要的。另外,在執行__main函數的過程中,不僅需要完成“使用微庫”情況下的所有工作,額外的工作還需要進行庫的初始化,才能使用系統庫(這一部分我還沒有深入)。使用微庫而不使用系統庫在程序連接時,不會把包含printf函數的庫連接到終極目標文件中,而使用我們定義的庫。啟動時需要完成的工作就是之前論述的步驟相比使用系統庫,啟動過程步驟更少。
6.總結
啟動文件XXX.s從頭開始執行,(C語言上分為棧、堆、.bss、.data、.code段)依次定義了棧,堆,代碼段|.text|,初始化向量表后又初始化了系統的時鍾的及C函數的跳轉,其中__main 是一個標准的C 庫函數,主要作用是初始化用戶堆棧(初始化數據段在.data段,未初始化數據段在.bss數據段上)最終調用main 函數。還需要清楚的一點是假設STM32被設置為從內部FLASH啟動中斷向量表起始地位為0x8000000; 則棧頂地址存放於0x8000000處,而復位中斷服務入口地址存放於0x8000004處。當STM32到復位信號后,則從0x80000004處取出復位中斷服務入口地址繼而執行復位中斷服務程序,; 然后跳轉__main函數最后在——main()函數的引導下進入C語言的用戶main()函數開始執行。