Preface

This article analyzes the STM32F103 startup file

1. STM32F103 system startup steps

The startup file is startup_stm32f10x_hd.s, which is written by assembly files and is the first program executed after the system is powered on.
The process is:
1. Set the heap and stack size, set the vector table
2, initialize the stack pointer
3, initialize the PC pointer = Rest_Handler
4, initialize the interrupt vector table
5, configure the system clock
6, call the C library function _main to initialize the user stack, thus Implement the main function

2. Start-up file code analysis

Stack stack size setting

Stack_Size      EQU     0x00000400
                AREA    STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem       SPACE   Stack_Size
__initial_sp

1. Set the stack size to 0x00000400 (1M size)
2. The function of the stack: save local variables, function calls, function parameters and other overheads. The size of the stack cannot exceed the internal SRAM.
3. AREA: Tell the assembler that it is a code segment or a data segment. STACK represents the stack name. It can be named arbitrarily; NOINIT means no initialization; READWRITE means readable and writable; ALIGN=3 alignment 2^3 power alignment, that is, 8-byte alignment, SPACE is used to allocate a certain size of memory, and the specified here is Stack_Size
4 , __Initial_sp, after SPACE, represents the end address of the stack, that is, the address of the top of the stack, the stack grows from high to low

Heap

Heap_Size       EQU     0x00000200
                AREA    HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem        SPACE   Heap_Size
__heap_limit
                PRESERVE8
                THUMB

1. Heap_Size is set to 0x00000200 (512 bytes)
2. __heap_base represents the start address of the heap, and __heap_limit represents the end address.
3. The heap grows from low to high.
4. The heap is used to dynamically allocate memory. The memory allocated by a series of malloc functions is on the heap.
5, PRESERVE8: indicates that the stack is aligned according to 8 bytes
6, THUMB: indicates that the thumb instruction set is used

Vector table

; Vector Table Mapped to Address 0 at Reset
                AREA    RESET, DATA, READONLY
                EXPORT  __Vectors
                EXPORT  __Vectors_End
                EXPORT  __Vectors_Size

Define a data segment named RESET, which is only readable. And EXPORT declares __Vectors, __Vectors_End, __Vectors_Size three attributes for external use.

Interrupt vector

When the kernel responds to an exception, the corresponding exception service will be executed. The kernel uses the interrupt vector table to indicate the entry address.

__Vectors       DCD     __initial_sp               ; Top of Stack 申请的栈顶，__Vectors对外的向量起始地址
                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
                ; External Interrupts
                DCD     WWDG_IRQHandler            ; Window Watchdog
                DCD     PVD_IRQHandler             ; PVD through EXTI Line detect
                DCD     TAMPER_IRQHandler          ; Tamper
__Vectors_End
          
__Vectors_Size  EQU  __Vectors_End - __Vectors

The vector table has system interrupts and peripheral interrupts. There are many vectors, and many are omitted here.
__Vectors is the start address of the vector, __Vectors_End is the end address, and __Vectors_Size is the size of the stack. The vector table is stored starting from address 0 of FLASH, with 4 bytes as a unit. The interrupt table stores the names of interrupt functions.

Code snippet

AREA    |.text|, CODE, READONLY

Define a code segment, readable

Reset program, entry function

Reset_Handler   PROC
                EXPORT  Reset_Handler             [WEAK]
                IMPORT  __main
                IMPORT  SystemInit
                LDR     R0, =SystemInit
                BLX     R0               
                LDR     R0, =__main
                BX      R0
                ENDP

The reset program is the first program executed. It initializes the system clock and jumps to the main function. __main is a standard C function library, which is mainly used to initialize the user stack and jump to the world of main C language.

                 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;用户初始化堆栈
                 LDR     R0, =  Heap_Mem
                 LDR     R1, =(Stack_Mem + Stack_Size)#计算栈大小
                 LDR     R2, = (Heap_Mem +  Heap_Size)#计算堆大小
                 LDR     R3, = Stack_Mem
                 BX      LR
                 ALIGN
                 ENDIF
                 END

STM32F103 system startup file analysis

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