cortex-m4启动代码解读

Posted 2020-12-25 franzz

1.启动代码最好结合链接脚本一起看
2.本文为nordic nrf52840的启动脚本，解释权归nordic所有
3.限于本人所学，难免出现错误，请不惜指出
4.在调试启动代码过程中，难免发生错误，不要惊慌，先冷静一下，尽可能的分析下可能出现的地方，尝试着修改，
看能否成功，如果还是不行的话，那么有两种可行的调试方案：
1)添加led灯信号,用来调试
2)修改Makefile,添加反汇编打印信息，利用jlink-commander进行单步调试(用IAR或Keil也可以)
/*
Copyright (c) 2009-2017 ARM Limited. All rights reserved.

SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the License); you may
not use this file except in compliance with the License.
You may obtain a copy of the License at

www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an AS IS BASIS, WITHOUTdf
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

NOTICE: This file has been modified by Nordic Semiconductor ASA.

*/

.syntax unified
.arch armv7e-m //armv7e-m架构

#ifdef __STARTUP_CONFIG
#include "startup_config.h"
#ifndef __STARTUP_CONFIG_STACK_ALIGNEMENT
#define __STARTUP_CONFIG_STACK_ALIGNEMENT 3
#endif
#endif

.section .stack //定义栈段
.align 3 // 2^3=8,即堆栈段8字节对齐
.equ Stack_Size, 8192 //定义堆栈大小(单位应该是k)

.globl __StackTop //定义栈顶(全局变量)
.globl __StackLimit //定义栈
__StackLimit:
.space Stack_Size //开辟Stack_Size大小空间
.size __StackLimit, . - __StackLimit
// __StackLimit代表栈的栈底，__StackLimit = . - __StackLimit
__StackLimit = __StackTop - SIZEOF(.stack_dummy);
__StackTop:
.size __StackTop, . - __StackTop
//栈顶(栈是向下增长的)
__StackTop = ORIGIN(RAM) + LENGTH(RAM);

.section .heap
.align 3
.equ Heap_Size, 8192

.globl __HeapBase //堆底(堆向上增长)
.globl __HeapLimit //堆顶
__HeapBase:
.if Heap_Size
.space Heap_Size
.endif
.size __HeapBase, . - __HeapBase
__HeapLimit:
.size __HeapLimit, . - __HeapLimit

.section .isr_vector //isr_vector段
.align 2 //2^2=4,4字节对齐
.globl __isr_vector //向量表
__isr_vector:
.long __StackTop /* Top of Stack */
.long Reset_Handler
.long NMI_Handler
.long HardFault_Handler
.long MemoryManagement_Handler
.long BusFault_Handler
.long UsageFault_Handler
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long SVC_Handler
.long DebugMon_Handler
.long 0 /*Reserved */
.long PendSV_Handler
.long SysTick_Handler

/* External Interrupts */
.long POWER_CLOCK_IRQHandler
.long RADIO_IRQHandler
.long UARTE0_UART0_IRQHandler
.long SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0_IRQHandler
.long SPIM1_SPIS1_TWIM1_TWIS1_SPI1_TWI1_IRQHandler
.long NFCT_IRQHandler
.long GPIOTE_IRQHandler
.long SAADC_IRQHandler
.long TIMER0_IRQHandler
.long TIMER1_IRQHandler
.long TIMER2_IRQHandler
.long RTC0_IRQHandler
.long TEMP_IRQHandler
.long RNG_IRQHandler
.long ECB_IRQHandler
.long CCM_AAR_IRQHandler
.long WDT_IRQHandler
.long RTC1_IRQHandler
.long QDEC_IRQHandler
.long COMP_LPCOMP_IRQHandler
.long SWI0_EGU0_IRQHandler
.long SWI1_EGU1_IRQHandler
.long SWI2_EGU2_IRQHandler
.long SWI3_EGU3_IRQHandler
.long SWI4_EGU4_IRQHandler
.long SWI5_EGU5_IRQHandler
.long TIMER3_IRQHandler
.long TIMER4_IRQHandler
.long PWM0_IRQHandler
.long PDM_IRQHandler
.long 0 /*Reserved */
.long 0 /*Reserved */
.long MWU_IRQHandler
.long PWM1_IRQHandler
.long PWM2_IRQHandler
.long SPIM2_SPIS2_SPI2_IRQHandler
.long RTC2_IRQHandler
.long I2S_IRQHandler
.long FPU_IRQHandler
.long USBD_IRQHandler
.long UARTE1_IRQHandler
.long QSPI_IRQHandler
.long CRYPTOCELL_IRQHandler
.long 0 /*Reserved */
.long 0 /*Reserved */
.long PWM3_IRQHandler
.long 0 /*Reserved */
.long SPIM3_IRQHandler
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */
.long 0 /*Reserved */

.size __isr_vector, . - __isr_vector

/* Reset Handler */

.text
.thumb //支持thumb指令
.thumb_func
.align 1 //2字节对齐(写汇编时需注意)
.globl Reset_Handler
.type Reset_Handler, %function
Reset_Handler:

/* Loop to copy data from read only memory to RAM.
* 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.
* __bss_start__: VMA of end of the section to copy to. Normally __data_end__ is used, but by using __bss_start__
* the user can add their own initialized data section before BSS section with the INTERT AFTER command.
*
* All addresses must be aligned to 4 bytes boundary.
*/
ldr r1, =__etext //重定位数据段
//注意在cortex-m4中thumb是2字节对齐的
//按照以往的写法往往会导致未定义指令异常，因此，这种情况下推荐使用
//c来实现重定位和初始化
ldr r2, =__data_start__
ldr r3, =__bss_start__

subs r3, r2
ble .L_loop1_done

.L_loop1:
subs r3, #4
ldr r0, [r1,r3]
str r0, [r2,r3]
bgt .L_loop1

.L_loop1_done:

/* This part of work usually is done in C library startup code. Otherwise,
* define __STARTUP_CLEAR_BSS to enable it in this startup. This section
* clears the RAM where BSS data is located.
*
* The BSS section is specified by following symbols
* __bss_start__: start of the BSS section.
* __bss_end__: end of the BSS section.
*
* All addresses must be aligned to 4 bytes boundary.
*/
#ifdef __STARTUP_CLEAR_BSS
ldr r1, =__bss_start__
ldr r2, =__bss_end__

movs r0, 0

subs r2, r1
ble .L_loop3_done

.L_loop3:
subs r2, #4
str r0, [r1, r2]
bgt .L_loop3

.L_loop3_done:
#endif /* __STARTUP_CLEAR_BSS */

bl bsp_board_leds_init
/* Execute SystemInit function. */
bl SystemInit

/* Call _start function provided by libraries.
* If those libraries are not accessible, define __START as your entry point.
*/
#if 1
#ifndef __START
#define __START _start
#endif
bl __libc_init_array
bl __START
#else
bl main //做了一些修改，直接跳到main函数，这样容易理解
#endif
.pool
.size Reset_Handler,.-Reset_Handler

.section ".text"

/* Dummy Exception Handlers (infinite loops which can be modified) */

.weak NMI_Handler
.type NMI_Handler, %function
NMI_Handler:
b .
.size NMI_Handler, . - NMI_Handler

.weak HardFault_Handler
.type HardFault_Handler, %function
HardFault_Handler:
b .
.size HardFault_Handler, . - HardFault_Handler

.weak MemoryManagement_Handler
.type MemoryManagement_Handler, %function
MemoryManagement_Handler:
b .
.size MemoryManagement_Handler, . - MemoryManagement_Handler

.weak BusFault_Handler
.type BusFault_Handler, %function
BusFault_Handler:
b .
.size BusFault_Handler, . - BusFault_Handler

.weak UsageFault_Handler
.type UsageFault_Handler, %function
UsageFault_Handler:
b .
.size UsageFault_Handler, . - UsageFault_Handler

.weak SVC_Handler
.type SVC_Handler, %function
SVC_Handler:
b .
.size SVC_Handler, . - SVC_Handler

.weak DebugMon_Handler
.type DebugMon_Handler, %function
DebugMon_Handler:
b .
.size DebugMon_Handler, . - DebugMon_Handler

.weak PendSV_Handler
.type PendSV_Handler, %function
PendSV_Handler:
b .
.size PendSV_Handler, . - PendSV_Handler

.weak SysTick_Handler
.type SysTick_Handler, %function
SysTick_Handler:
b .
.size SysTick_Handler, . - SysTick_Handler

/* IRQ Handlers */

.globl Default_Handler
.type Default_Handler, %function
Default_Handler:
b .
.size Default_Handler, . - Default_Handler

.macro IRQ handler
.weak handler
.set handler, Default_Handler
.endm

IRQ POWER_CLOCK_IRQHandler
IRQ RADIO_IRQHandler
IRQ UARTE0_UART0_IRQHandler
IRQ SPIM0_SPIS0_TWIM0_TWIS0_SPI0_TWI0_IRQHandler
IRQ SPIM1_SPIS1_TWIM1_TWIS1_SPI1_TWI1_IRQHandler
IRQ NFCT_IRQHandler
IRQ GPIOTE_IRQHandler
IRQ SAADC_IRQHandler
IRQ TIMER0_IRQHandler
IRQ TIMER1_IRQHandler
IRQ TIMER2_IRQHandler
IRQ RTC0_IRQHandler
IRQ TEMP_IRQHandler
IRQ RNG_IRQHandler
IRQ ECB_IRQHandler
IRQ CCM_AAR_IRQHandler
IRQ WDT_IRQHandler
IRQ RTC1_IRQHandler
IRQ QDEC_IRQHandler
IRQ COMP_LPCOMP_IRQHandler
IRQ SWI0_EGU0_IRQHandler
IRQ SWI1_EGU1_IRQHandler
IRQ SWI2_EGU2_IRQHandler
IRQ SWI3_EGU3_IRQHandler
IRQ SWI4_EGU4_IRQHandler
IRQ SWI5_EGU5_IRQHandler
IRQ TIMER3_IRQHandler
IRQ TIMER4_IRQHandler
IRQ PWM0_IRQHandler
IRQ PDM_IRQHandler
IRQ MWU_IRQHandler
IRQ PWM1_IRQHandler
IRQ PWM2_IRQHandler
IRQ SPIM2_SPIS2_SPI2_IRQHandler
IRQ RTC2_IRQHandler
IRQ I2S_IRQHandler
IRQ FPU_IRQHandler
IRQ USBD_IRQHandler
IRQ UARTE1_IRQHandler
IRQ QSPI_IRQHandler
IRQ CRYPTOCELL_IRQHandler
IRQ PWM3_IRQHandler
IRQ SPIM3_IRQHandler

.end