startup_ARMCM7.S 分析

/* 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

posted @ 2020-12-12 23:15  一豆羹  阅读(598)  评论(0编辑  收藏  举报