[嵌入式]STM32MP157学习--Reset_Handler函数

如果是使用stm32cubeide编译的话是会用到gcc/linker文件下的startup_stm32mp15xx.s，当然了如果是用mdk的话是纯纯的汇编它是在arm/linker文件夹下的startup_stm32mp15xx.s这两个文件功能是一样的只是编写风格十分不同，如果是想看mdk的说明可以移步本站的其他文章。

其代码如下，十分的简洁，而且熟悉arm汇编的话，很容易就能理解

Reset_Handler   PROC
                EXPORT   Reset_Handler             [WEAK]
                IMPORT   SystemInit
                IMPORT   __main

                LDR      R0, =SystemInit
                BLX      R0
                LDR      R0, =__main
                BX       R0
                ENDP

当然了今天的主角是下面的采用stm32cubeide的编写风格的汇编

  .section .startup_copro_fw.Reset_Handler,"ax"
  .weak Reset_Handler
  .type Reset_Handler, %function
Reset_Handler:
  ldr   sp, =_estack      /* set stack pointer */

/*     Loop to copy data from read only memory to RAM. The ranges
 *      of copy from/to are specified by following symbols evaluated in
 *      linker script.
 *      _sidata: End of code section, i.e., begin of data sections to copy from.
 *      _sdata/_edata: RAM address range that data should be
 *      copied to. Both must be aligned to 4 bytes boundary.  */
  movs  r1, #0
  b  LoopCopyDataInit

CopyDataInit:
  ldr  r3, =_sidata
  ldr  r3, [r3, r1]
  str  r3, [r0, r1]
  adds  r1, r1, #4
    
LoopCopyDataInit:
  ldr  r0, =_sdata
  ldr  r3, =_edata
  adds  r2, r0, r1
  cmp  r2, r3
  bcc  CopyDataInit
  ldr  r2, =_sbss
  b  LoopFillZerobss
  
/* Zero fill the bss segment. */  
FillZerobss:
  movs  r3, #0
  str  r3, [r2], #4
    
LoopFillZerobss:
  ldr  r3, = _ebss
  cmp  r2, r3
  bcc  FillZerobss
  
/* Call the clock system intitialization function.*/

  bl  SystemInit
 // ldr r0, =SystemInit
 // blx r0
/* Call static constructors */
 bl __libc_init_array
 // ldr r0, =__libc_init_array
 // blx r0
/* Call the application's entry point.*/
  bl main
  //ldr r0, =main
  //blx r0

LoopForever:
    b LoopForever


.size Reset_Handler, .-Reset_Handler

可以在最后的代码段看到如下的代码，它和arm下的汇编的意思是一样的，都是先跳转到systeminit(?bl? SystemInit),再跳转到main(bl main)函数

/* Call the clock system intitialization function.*/
  bl  SystemInit
 // ldr r0, =SystemInit
 // blx r0
/* Call static constructors */
 bl __libc_init_array
 // ldr r0, =__libc_init_array
 // blx r0
/* Call the application's entry point.*/
  bl main
  //ldr r0, =main
  //blx r0

LoopForever:
    b LoopForever

从注释中可以看到：

1、/* Call the clock system intitialization function.*/

该处是调用时钟系统初始化函数。

2、/* Call the application's entry point.*/

该处是调用应用程序的入口指针（点位）。