_{對于keil的啟動(dòng)代碼（針對STM32F042），添加 備注 和 自己的理解}

;******************** (C) COPYRIGHT 2014 STMicroelectronics ********************
;* File Name     : startup_stm32f042.s
;* Author       : MCD Application Team,modified by Sky,
;* Version      : V1.5.0;* Date        : 05-December-2014,modified on,01-Nov-2016;* Description    : STM32F042 Devices vector table for;*           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 CortexM0 processor is in Thread mode,
;*           priority is Privileged, and the Stack is set to Main.
;* <<< Use Configuration Wizard in Context Menu >>>  
;*******************************************************************************
; @attention
; 
; 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.
; 
;*******************************************************************************




;
;
;notes:stack,heap,data seg,code seg address of mem is set by compiler
;
;










;
; Amount of memory (in bytes) allocated for Stack
; Tailor this value to your application needs
;  Stack Configuration
;   Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
; 

;;EQU 定義宏
;;棧大小，1k
Stack_Size   EQU   0x00000400;;AREA 定義段，注意：一個(gè)程序是由多個(gè)段構(gòu)成，如CODE，STACK，DATA，
;;ALIGN=3,8字節(jié)對齊
        AREA  STACK, NOINIT, READWRITE, ALIGN=3Stack_Mem    SPACE  Stack_Size
;;__initial_sp一個(gè)標(biāo)號,由匯編器進(jìn)行計(jì)算，代表上面SPACE分配內(nèi)存的最后一個(gè)地址，棧為向下增長型
__initial_sp


;  Heap Configuration
;   Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
; 
;;堆512bytes
Heap_Size    EQU   0x00000200

        AREA  HEAP, NOINIT, READWRITE, ALIGN=3__heap_base
Heap_Mem    SPACE  Heap_Size
__heap_limit
;;PRESERVE8,指定當(dāng)前文件堆棧8bytes對齊
        PRESERVE8
;;THUMB，后面的指令要兼容THUMB指令
        THUMB


; Vector Table Mapped to Address 0 at Reset
;;定義一個(gè)叫做RESET的數(shù)據(jù)段
        AREA  RESET, DATA, READONLY
;;EXPORT聲明標(biāo)號為外部文件可用
        EXPORT __Vectors
        EXPORT __Vectors_End
        EXPORT __Vectors_Size
;;DCD是按4字節(jié)分配存儲單元
__Vectors    DCD   __initial_sp          ; Top of Stack
            DCD   Reset_Handler         ; Reset Handler
            DCD   NMI_Handler          ; NMI Handler
            DCD   HardFault_Handler       ; Hard Fault Handler
            DCD   0               ; Reserved
            DCD   0               ; Reserved
            DCD   0               ; Reserved
            DCD   0               ; Reserved
            DCD   0               ; Reserved
            DCD   0               ; Reserved
            DCD   0               ; Reserved
            DCD   SVC_Handler          ; SVCall Handler
            DCD   0               ; Reserved
            DCD   0               ; Reserved
            DCD   PendSV_Handler         ; PendSV Handler
            DCD   SysTick_Handler        ; SysTick Handler

        ; External Interrupts
        DCD   WWDG_IRQHandler        ; Window Watchdog
        DCD   PVD_VDDIO2_IRQHandler     ; PVD and VDDIO2 through EXTI Line detect
        DCD   RTC_IRQHandler         ; RTC through EXTI Line
        DCD   FLASH_IRQHandler        ; FLASH
        DCD   RCC_CRS_IRQHandler       ; RCC and CRS
        DCD   EXTI0_1_IRQHandler       ; EXTI Line 0 and 1
        DCD   EXTI2_3_IRQHandler       ; EXTI Line 2 and 3
        DCD   EXTI4_15_IRQHandler      ; EXTI Line 4 to 15
        DCD   TSC_IRQHandler         ; TS
        DCD   DMA1_Channel1_IRQHandler    ; DMA1 Channel 1
        DCD   DMA1_Channel2_3_IRQHandler   ; DMA1 Channel 2 and Channel 3
        DCD   DMA1_Channel4_5_IRQHandler   ; DMA1 Channel 4, Channel 5
        DCD   ADC1_IRQHandler        ; ADC1 
        DCD   TIM1_BRK_UP_TRG_COM_IRQHandler ; TIM1 Break, Update, Trigger and Commutation
        DCD   TIM1_CC_IRQHandler       ; TIM1 Capture Compare
        DCD   TIM2_IRQHandler        ; TIM2
        DCD   TIM3_IRQHandler        ; TIM3
        DCD   0               ; Reserved
        DCD   0               ; Reserved
        DCD   TIM14_IRQHandler        ; TIM14
        DCD   0               ; Reserved
        DCD   TIM16_IRQHandler        ; TIM16
        DCD   TIM17_IRQHandler        ; TIM17
        DCD   I2C1_IRQHandler        ; I2C1
        DCD   0               ; Reserved
        DCD   SPI1_IRQHandler        ; SPI1
        DCD   SPI2_IRQHandler        ; SPI2
        DCD   USART1_IRQHandler       ; USART1
        DCD   USART2_IRQHandler       ; USART2
        DCD   0               ; Reserved
        DCD   CEC_CAN_IRQHandler       ; CEC and CAN
        DCD   USB_IRQHandler         ; USB

__Vectors_End

__Vectors_Size EQU __Vectors_End - __Vectors

;;定義一個(gè).text的代碼段
        AREA  |.text|, CODE, READONLY

;STM32F03x devices feature 4Kbytes of static SRAM. STM32F04x devices feature
;6 Kbytes of static SRAM. STM32F05x devices feature 8Kbytes of static SRAM.
;STM32F07xS devices feature 16 Kbytes of static SRAM. STM32F09x devices feature
;32 Kbytes of static SRAM.





; Reset handler routine
;;PROC定義子程序
Reset_Handler  PROC 
;;WEAK:弱定義
         EXPORT Reset_Handler         [WEAK]
    IMPORT __main
    IMPORT SystemInit


;;給R0賦值，sp的值
    LDR   R0, =__initial_sp     ; set stack pointer 
;;R0給MSP寄存器
    MSR   MSP, R0 

;;Check if boot space corresponds to test memory 

    LDR R0,=0x00000004
    LDR R1, [R0]
    ;;R1=0x08000004 OR R1=0x20000004 OR R1=0x1FXX XXXX
    ;;when R1=R1=0x1FXX XXXX,we can know that Reset_Handler'sAddress is not right,
    ;;it maybe in reserved or systemmemory or optionbyte，we must remap address for start 
;;Logical shift right by register LSRS

    LSRS R1, R1, #24
    ;R2=0x0000001F
    LDR R2,=0x1F
    CMP R1, R2

    BNE ApplicationStart 

;; SYSCFG clock enable  
   ;RCC_APB2ENR,0x40021018 
    LDR R0,=0x40021018 
    LDR R1,=0x00000001
    STR R1, [R0]

;; Set CFGR1 register with flash memory remap at address 0
   ;SYS_CFGR1,0x40010000 
    LDR R0,=0x40010000 
    LDR R1,=0x00000000
    STR R1, [R0]
ApplicationStart
         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 .  無限循環(huán)
        B    .
        ENDP
HardFault_Handler
        PROC
        EXPORT HardFault_Handler       [WEAK]
        B    .
        ENDP
SVC_Handler   PROC
        EXPORT SVC_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_VDDIO2_IRQHandler     [WEAK]
        EXPORT RTC_IRQHandler         [WEAK]
        EXPORT FLASH_IRQHandler        [WEAK]
        EXPORT RCC_CRS_IRQHandler       [WEAK]
        EXPORT EXTI0_1_IRQHandler       [WEAK]
        EXPORT EXTI2_3_IRQHandler       [WEAK]
        EXPORT EXTI4_15_IRQHandler      [WEAK]
        EXPORT TSC_IRQHandler         [WEAK]
        EXPORT DMA1_Channel1_IRQHandler    [WEAK]
        EXPORT DMA1_Channel2_3_IRQHandler   [WEAK]
        EXPORT DMA1_Channel4_5_IRQHandler   [WEAK]
        EXPORT ADC1_IRQHandler        [WEAK]
        EXPORT TIM1_BRK_UP_TRG_COM_IRQHandler [WEAK]
        EXPORT TIM1_CC_IRQHandler       [WEAK]
        EXPORT TIM2_IRQHandler        [WEAK]
        EXPORT TIM3_IRQHandler        [WEAK]
        EXPORT TIM14_IRQHandler        [WEAK]
        EXPORT TIM16_IRQHandler        [WEAK]
        EXPORT TIM17_IRQHandler        [WEAK]
        EXPORT I2C1_IRQHandler        [WEAK]
        EXPORT SPI1_IRQHandler        [WEAK]
        EXPORT SPI2_IRQHandler        [WEAK]
        EXPORT USART1_IRQHandler       [WEAK]
        EXPORT USART2_IRQHandler       [WEAK]
        EXPORT CEC_CAN_IRQHandler       [WEAK]
        EXPORT USB_IRQHandler         [WEAK]


WWDG_IRQHandler
PVD_VDDIO2_IRQHandler
RTC_IRQHandler
FLASH_IRQHandler
RCC_CRS_IRQHandler
EXTI0_1_IRQHandler
EXTI2_3_IRQHandler
EXTI4_15_IRQHandler
TSC_IRQHandler
DMA1_Channel1_IRQHandler
DMA1_Channel2_3_IRQHandler
DMA1_Channel4_5_IRQHandler
ADC1_IRQHandler 
TIM1_BRK_UP_TRG_COM_IRQHandler
TIM1_CC_IRQHandler
TIM2_IRQHandler
TIM3_IRQHandler
TIM14_IRQHandler
TIM16_IRQHandler
TIM17_IRQHandler
I2C1_IRQHandler
SPI1_IRQHandler
SPI2_IRQHandler
USART1_IRQHandler
USART2_IRQHandler
CEC_CAN_IRQHandler
USB_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*****