u-boot第二阶段之start_armboot（）函数

1、#ifdef CONFIG_MEMORY_UPPER_CODE /* by scsuh */
ulong gd_base;


gd_base = CFG_UBOOT_BASE + CFG_UBOOT_SIZE - CFG_MALLOC_LEN - CFG_STACK_SIZE - sizeof(gd_t);
#ifdef CONFIG_USE_IRQ
gd_base -= (CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ);
#endif
gd = (gd_t*)gd_base;
#else
gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));
#endif


/* compiler optimization barrier needed for GCC >= 3.4 */
__asm__ __volatile__("": : :"memory");


memset ((void*)gd, 0, sizeof (gd_t));
gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));

memset (gd->bd, 0, sizeof (bd_t));

为gd_t和bd_t结构体分配内存并初始化

2、调用通用初始化函数 

for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) { 


           if ((*init_fnc_ptr)() != 0) { 
                hang (); 
           } 


      } 
init_sequence[]是init_fnc_t 函数指针数组，这个数组包含了众多初始化函数，比如cpu_init， 
board_init 等。 


                  //init_fnc_t *init_sequence[] = { 


                      //   cpu_init,        /* basic cpu dependent setup */ 


                      //   board_init,         /* basic board dependent setup */ 


                     //    interrupt_init,        /* set up exceptions */ 


                     //    env_init,        /* initialize environment */ 


                      //   init_baudrate,         /* initialze baudrate settings */ 


                    //     serial_init,       /* serial communications setup */ 


                    //     display_banner, 


                    //     dram_init,         /* configure available RAM banks */ 


                    //     display_dram_config, 


                    //     NULL, 


                    //     }; 

3、具体设备初始化

#ifndef CFG_NO_FLASH
/* configure available FLASH banks */
size = flash_init ();
display_flash_config (size);
#endif /* CFG_NO_FLASH */


#ifdef CONFIG_VFD
# ifndef PAGE_SIZE
#  define PAGE_SIZE 4096
# endif
/*
* reserve memory for VFD display (always full pages)
*/
/* bss_end is defined in the board-specific linker script */
addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
size = vfd_setmem (addr);
gd->fb_base = addr;
#endif /* CONFIG_VFD */


#ifdef CONFIG_LCD
# ifndef PAGE_SIZE
#  define PAGE_SIZE 4096
# endif
/*
* reserve memory for LCD display (always full pages)
*/
/* bss_end is defined in the board-specific linker script */
addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
size = lcd_setmem (addr);
gd->fb_base = addr;
#endif /* CONFIG_LCD */


/* armboot_start is defined in the board-specific linker script */
#ifdef CONFIG_MEMORY_UPPER_CODE /* by scsuh */
mem_malloc_init (CFG_UBOOT_BASE + CFG_UBOOT_SIZE - CFG_MALLOC_LEN - CFG_STACK_SIZE);
#else
mem_malloc_init (_armboot_start - CFG_MALLOC_LEN);
#endif


#if defined(CONFIG_SMDK6400) || defined(CONFIG_SMDK6410) || defined(CONFIG_SMDK6430) || defined(CONFIG_SMDK2450) || defined(CONFIG_SMDK2416)


   #if defined(CONFIG_NAND)
    puts ("NAND:    ");
    nand_init(); /* go init the NAND */
   #endif
    
    #if defined(CONFIG_ONENAND)
    puts ("OneNAND: ");
    onenand_init(); /* go init the One-NAND */
    #endif
    
    #if defined(CONFIG_BOOT_MOVINAND)
    puts ("SD/MMC:  ");
    
    if ((0x24564236 == magic[0]) && (0x20764316 == magic[1])) {
    printf("Boot up for burning\n");
    } else {
    movi_set_capacity();
    movi_set_ofs(MOVI_TOTAL_BLKCNT);
    movi_init();
    }
    #endif


#else


  #if (CONFIG_COMMANDS & CFG_CMD_NAND)
  puts ("NAND:    ");
  nand_init(); /* go init the NAND */
  #endif


#endif

4、环境变量初始化

环境变量在通用初始化函数里面，已经初始化一次（env_init ），这里调用env_relocate 对环 

境变量进行重新定位。

/* initialize environment */
env_relocate ();

5、进入主循环

/* main_loop() can return to retry autoboot, if so just run it again. */
for (;;) {
main_loop ();
}