基于keil的嵌入式代码启动过程
一般来讲，基于我本人的认知，keil工程新建时，需要导入基于MCU芯片的“.s”文件。它就是keil默认的，用来启动整个嵌入式系统的汇编文件
以STM32F4xx为例，启动过程包括了：堆栈空间定义、中断向量表、复位中断函数、其他中断服务函数、库函数初始化
1、堆栈空间定义
栈大小定义 0x400，即1024字节
Stack_Size EQU 0x00000400
AREA STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem SPACE Stack_Size
__initial_sp
堆大小定义 0x200，即512字节
Heap_Size EQU 0x00000200
AREA HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem SPACE Heap_Size
__heap_limit
它们的空间由SPACE关键字来申请，并记作Stack_Mem和Heap_Mem；还定义了三个标号：__initial_sp（栈顶）、__heap_base（堆起始地址）和__heap_limit（堆终止地址）
2、中断向量表
由DCD申请空间存放的一个个函数入口，即中断向量表。
关键字DCD代表申请一个字的空间，后面的函数名即为中断服务函数入口地址；断向量表一般存放在Flash 0地址。
__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 FMC_IRQHandler ; FMC
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 0 ; Reserved
DCD HASH_RNG_IRQHandler ; Hash and Rng
DCD FPU_IRQHandler ; FPU
__Vectors_End
3、复位中断函数
程序上电后，首先加载SP和PC，ARM规定从0地址处加载SP，从偏移为4的地址（0x00000004）处加载PC。然后将程序控制权交给程序。我们知道0地址处存放__initial_sp，0x00000004地址处存放Reset_Handler，加载PC后，程序跳转到Reset_Handler开始运行。
而Reset_Handler中，首先调用SystemInit函数来进行硬件初始化（主要是时钟），然后调用__main函数（由keil微库或者C库实现），最后调用用户自定义的main()。
; Reset handler
Reset_Handler PROC
EXPORT Reset_Handler [WEAK]
IMPORT SystemInit
IMPORT __main
LDR R0, =SystemInit
BLX R0
LDR R0, =__main
BX R0
ENDP
4、其他中断服务函数
比较基础，不具体展开
5、库函数初始化
如果勾选【Options for Target】->【Target】->【Use MicroLIB】,如下图所示。即使用微库，则__MICROLIB会被定义，编译器编译IF的代码，即：__initial_sp、__heap_base和__heap_limit
;*******************************************************************************
; 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
如果不勾选【Use MicroLIB】，则缺省使用KEIL C库，KEIL C库函数会调用__user_initial_stackheap，通过R0~R3将堆栈以参数形式传递给KEIL C库
在我的rtThread系统中（基于3.0.3版本），会首先调用component.c下的main函数
extern int $Super$$main(void);
/* re-define main function */
int $Sub$$main(void)
{
rt_hw_interrupt_disable();
rtthread_startup();
return 0;
}
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版权声明：本文为CSDN博主「KST_Ai9」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/KST_Ai9/article/details/131277419
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