二、RT-Thread启动流程详解（硬件初始化篇）

备注：基于正点原子阿波罗STM32F767IGT6开发板，RT-Thread Studio开发环境

目录

1、入口函数的确认

2、函数执行流程 

3、关键函数功能详解

3.1 Reset_Handler

3.2 SystemInit()

3.3 entry()

3.4 rtthread_startup

3.4 rt_hw_interrupt_disable

3.4 rt_hw_board_init

3.5 hw_board_init

3.6 rt_console_set_device

3.7 rt_components_board_init

3.8 rt_show_version

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1、入口函数的确认

    编译工具链为arm-none-eabi，根据链接文件link.lds中的关键字ENTRY可以确认程序的入口地址是Reset_Handler。

/*
 * linker script for STM32F767IG with GNU ld
 */

/* Program Entry, set to mark it as "used" and avoid gc */
MEMORY
{
    ROM (rx) : ORIGIN = 0x08000000, LENGTH =  1024k /* 1024K flash */
    RAM (rw) : ORIGIN = 0x20020000, LENGTH =  384k /* 384K sram */
}
ENTRY(Reset_Handler)
_system_stack_size = 0x400;

2、函数执行流程 

一图流，如图2.2.1

图2.2.1

3、关键函数功能详解

函数功能讲解增加到了代码注释中。

3.1 Reset_Handler

  主板上电复位后从Reset_Handler开始执行，在进入SystemInit函数前，主要做了如下事情：

  3.1.1 设置SP栈指针；

  3.1.2 data段数据从flash搬运到SRAM；

  3.1.3 bss段清零，然后跳转至SystemInit； 注意：地址相关信息均由link.lds链接文件在编译时确定。

  .section  .text.Reset_Handler
  .weak  Reset_Handler
  .type  Reset_Handler, %function
Reset_Handler:  
    ldr   sp, =_estack 	/* set stack pointer initialize, the '_estack' definition in the link file*/

/**
  * Data segment: Data stored at compile time (not at runtime) that can be read and written.
  * This is also known as static storage,
  * where initialized global variables and initialized static variables are stored,
  * and where constants are stored
  */
/* Copy the data segment initializers from flash to SRAM */  
    movs  r1, #0			/* save 0 to R1 */
    b  LoopCopyDataInit

CopyDataInit:				/* .data data copy */
    ldr  r3, =_sidata		/* R3 = The .data is at the starting address of Flash */
    ldr  r3, [r3, r1]		/* load the value of the [R3 + R1] address into R3 */
    str  r3, [r0, r1]		/* save the value of R3 to the address of [R0 + R1] */
    adds  r1, r1, #4		/* R1 = R1 + 4 */
    
LoopCopyDataInit:
    ldr  r0, =_sdata		/* assign the .data start address into R0 */
    ldr  r3, =_edata		/* assign the .data end address into R3 */
    adds  r2, r0, r1		/* r2 = r0 + r1, */
    cmp  r2, r3				/* compare R2 and R3 value */
    bcc  CopyDataInit		/* if R2 and R3 value not equality,  jump */
    ldr  r2, =_sbss			/* load  the .bss satrt address into R2 */
    b  LoopFillZerobss		/* jump to LoopFillZerobss */

/**
 * BSS section:
 * Global and static variables defined without initial values are placed in this section
 */
/* Zero fill the bss segment. */  
FillZerobss:
    movs  r3, #0			/* save 0 to R3 */
    str  r3, [r2], #4		/* save the value of R3 to the address of [R