/* File: startup_ARMCM7.S
* Purpose: startup file for Cortex-M7 devices. Should use with
* GCC for ARM Embedded Processors
* Version: V2.0
* Date: 01 August 2014
*
/* Copyright (c) 2011 - 2014 ARM LIMITED
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
- Neither the name of ARM nor the names of its contributors may be used
to endorse or promote products derived from this software without
specific prior written permission.
*
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL COPYRIGHT HOLDERS AND CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
---------------------------------------------------------------------------*/
.syntax unified @ ARM 和 THUMB 联合指令集（语法？）
.arch armv7e-m @ arm 版本
.section .stack @ 栈定义
.align 3 @ 8 字节对齐
#ifdef __STACK_SIZE
.equ Stack_Size, __STACK_SIZE
#else
.equ Stack_Size, 0xc00
#endif
.globl __StackTop
.globl __StackLimit
__StackLimit:
.space Stack_Size @ 置零 Stack_Size 大小的空间
.size __StackLimit, . - __StackLimit @ 设置__StackLimit的大小？
__StackTop:
.size __StackTop, . - __StackTop @ 设置__StackTop的大小？
.section .heap @ 堆定义
.align 3 @ 8 字节对齐
#ifdef __HEAP_SIZE
.equ Heap_Size, __HEAP_SIZE
#else
.equ Heap_Size, 0
#endif
.globl __HeapBase
.globl __HeapLimit
__HeapBase:
.if Heap_Size
.space Heap_Size
.endif
.size __HeapBase, . - __HeapBase
__HeapLimit:
.size __HeapLimit, . - __HeapLimit
.section .isr_vector @ 中断向量定义
.align 2 @ 4字节对齐
.globl __isr_vector
__isr_vector:
.long __StackTop /* Top of Stack */
.long Reset_Handler /* Reset Handler */
.long NMI_Handler /* NMI Handler */
.long HardFault_Handler /* Hard Fault Handler */
.long MemManage_Handler /* MPU Fault Handler */
.long BusFault_Handler /* Bus Fault Handler */
.long UsageFault_Handler /* Usage Fault Handler */
.long 0 /* Reserved */
.long 0 /* Reserved */
.long 0 /* Reserved */
.long 0 /* Reserved */
.long SVC_Handler /* SVCall Handler */
.long DebugMon_Handler /* Debug Monitor Handler */
.long 0 /* Reserved */
.long PendSV_Handler /* PendSV Handler */
.long SysTick_Handler /* SysTick Handler */
/* External interrupts */
.long Default_Handler
.size __isr_vector, . - __isr_vector
.text
.thumb
.thumb_func
.align 2
.globl Reset_Handler
.type Reset_Handler, %function @ 类型定义为函数
Reset_Handler:
/* Firstly it copies data from read only memory to RAM. There are two schemes
* to copy. One can copy more than one sections. Another can only copy
* one section. The former scheme needs more instructions and read-only
* data to implement than the latter.
* Macro __STARTUP_COPY_MULTIPLE is used to choose between two schemes. */
#ifdef __STARTUP_COPY_MULTIPLE
/* Multiple sections scheme.
*
* Between symbol address __copy_table_start__ and __copy_table_end__,
* there are array of triplets, each of which specify:
* offset 0: LMA of start of a section to copy from
* offset 4: VMA of start of a section to copy to
* offset 8: size of the section to copy. Must be multiply of 4
*
* All addresses must be aligned to 4 bytes boundary.
*/
ldr r4, =__copy_table_start__ @ [0]:拷贝数据源地址 [1]:拷贝数据目标地址 [2]:拷贝数据数目byte(4的倍数)
ldr r5, =__copy_table_end__ @ 多段复制信息存储结束地址
.L_loop0:
cmp r4, r5 @ r4 - r5
bge .L_loop0_done @ >= 复制完毕
ldr r1, [r4] @ r1 = 数据源地址
ldr r2, [r4, #4] @ r2 = 数据目标地址
ldr r3, [r4, #8] @ r3 = 数据byte
.L_loop0_0:
subs r3, #4 @ r3 = 数据byte - 4
ittt ge @ (https://stackoverflow.com/questions/7042289/itte-in-arm-assembly) >=, 则执行带有ge的指令, ttt表示顺延的3条than指令
ldrge r0, [r1, r3] @ 加载 r1 偏移 r3 后地址对应的数据 -> r0
strge r0, [r2, r3] @ r0 -> r2 偏移 r3 后地址
bge .L_loop0_0 @ r3>=4 则循环复制
adds r4, #12 @ 多段复制
b .L_loop0
.L_loop0_done:
#else
/* Single section scheme.
*
* The ranges of copy from/to are specified by following symbols
* __etext: LMA of start of the section to copy from. Usually end of text
* __data_start__: VMA of start of the section to copy to
* __data_end__: VMA of end of the section to copy to
*
* All addresses must be aligned to 4 bytes boundary.
*/
ldr r1, =__etext
ldr r2, =__data_start__
ldr r3, =__data_end__
.L_loop1:
cmp r2, r3
ittt lt
ldrlt r0, [r1], #4
strlt r0, [r2], #4
blt .L_loop1
#endif /*__STARTUP_COPY_MULTIPLE */
/* This part of work usually is done in C library startup code. Otherwise,
* define this macro to enable it in this startup.
*
* There are two schemes too. One can clear multiple BSS sections. Another
* can only clear one section. The former is more size expensive than the
* latter.
*
* Define macro __STARTUP_CLEAR_BSS_MULTIPLE to choose the former.
* Otherwise efine macro __STARTUP_CLEAR_BSS to choose the later.
*/
#ifdef __STARTUP_CLEAR_BSS_MULTIPLE
/* Multiple sections scheme.
*
* Between symbol address __copy_table_start__ and __copy_table_end__,
* there are array of tuples specifying:
* offset 0: Start of a BSS section
* offset 4: Size of this BSS section. Must be multiply of 4
*/
ldr r3, =__zero_table_start__ @ [0]:起始地址 [1]:byte数
ldr r4, =__zero_table_end__ @ 多段赋值信息存储结束地址
.L_loop2:
cmp r3, r4 @ r3 - r4
bge .L_loop2_done @ 赋值完毕
ldr r1, [r3] @ r1 = 起始地址
ldr r2, [r3, #4] @ r2 = byte数
movs r0, 0
.L_loop2_0:
subs r2, #4 @ r2 = r2 - 4
itt ge @ 若 r2 >= 0, 则执行下述 ge
strge r0, [r1, r2] @ 0 -> r1 offset r2
bge .L_loop2_0 @ 重复清零
adds r3, #8 @ 多段清零
b .L_loop2
.L_loop2_done:
#elif defined (__STARTUP_CLEAR_BSS)
/* Single BSS section scheme.
*
* The BSS section is specified by following symbols
* __bss_start__: start of the BSS section.
* __bss_end__: end of the BSS section.
*
* Both addresses must be aligned to 4 bytes boundary.
*/
ldr r1, =__bss_start__
ldr r2, =__bss_end__
movs r0, 0
.L_loop3:
cmp r1, r2
itt lt
strlt r0, [r1], #4
blt .L_loop3
#endif /* __STARTUP_CLEAR_BSS_MULTIPLE || __STARTUP_CLEAR_BSS */
#ifndef __NO_SYSTEM_INIT
bl SystemInit
#endif
#ifndef __START
#define __START _start
#endif
bl __START
.pool
.size Reset_Handler, . - Reset_Handler @ Reset_Handler 结束
.align 1 @ 2字节对齐
.thumb_func @ thumb 指令
.weak Default_Handler @ 弱定义
.type Default_Handler, %function
Default_Handler:
b . @ 跳转自己? 死循环? 使未定义的终端处理函数引用该函数，进入死循环，见下述代码
.size Default_Handler, . - Default_Handler
/* Macro to define default handlers. Default handler
* will be weak symbol and just dead loops. They can be
* overwritten by other handlers */
.macro def_irq_handler handler_name
.weak \handler_name
.set \handler_name, Default_Handler
.endm
def_irq_handler NMI_Handler
def_irq_handler HardFault_Handler
def_irq_handler MemManage_Handler
def_irq_handler BusFault_Handler
def_irq_handler UsageFault_Handler
def_irq_handler SVC_Handler
def_irq_handler DebugMon_Handler
def_irq_handler PendSV_Handler
def_irq_handler SysTick_Handler
def_irq_handler DEF_IRQHandler
.end
原文：https://www.cnblogs.com/OneToken/p/14127270.html