#PS：要转载请注明出处，本人版权所有
#PS:这个只是 《 我自己 》理解，如果和你的
#原则相冲突，请谅解，勿喷
对于keil的启动代码（针对STM32F042），添加 备注 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
; <h> Stack Configuration
; <o> Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>\
;;EQU 定义宏
;;栈大小，1k
Stack_Size EQU 0x00000400
;;AREA 定义段，注意：一个程序是由多个段构成，如CODE，STACK，DATA，
;;ALIGN=3,8字节对齐
AREA STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem SPACE Stack_Size
;;__initial_sp一个标号,由汇编器进行计算，代表上面SPACE分配内存的最后一个地址，栈为向下增长型
__initial_sp
; <h> Heap Configuration
; <o> Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>
;;堆512bytes
Heap_Size EQU 0x00000200
AREA HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem SPACE Heap_Size
__heap_limit
;;PRESERVE8,指定当前文件堆栈8bytes对齐
PRESERVE8
;;THUMB，后面的指令要兼容THUMB指令
THUMB
; Vector Table Mapped to Address 0 at Reset
;;定义一个叫做RESET的数据段
AREA RESET, DATA, READONLY
;;EXPORT声明标号为外部文件可用
EXPORT __Vectors
EXPORT __Vectors_End
EXPORT __Vectors_Size
;;DCD是按4字节分配存储单元
__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
;;定义一个.text的代码段
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定义子程序
Reset_Handler PROC
;;WEAK:弱定义
EXPORT Reset_Handler [WEAK]
IMPORT __main
IMPORT SystemInit
;;给R0赋值，sp的值
LDR R0, =__initial_sp ; set stack pointer
;;R0给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 . 无限循环
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*****
#PS：请尊重原创，不喜勿喷
#PS：要转载请注明出处，本人版权所有.
有问题请留言，看到后我会第一时间回复