uboot引导内核如何做到的我们不知道,但是大体上应该是:start_armboot开始执行一个3秒计时,如果我们没有按键的话就开始引导内核,如果按了的话就等待输入命令。
这些在启动的输出参数里面可以看到,uboot源码阅读(七)开发板启动串口输出,这里有我的开发板的输出信息。
CPU: S3C6410@532MHz
Fclk = 532MHz, Hclk = 133MHz, Pclk = 66MHz, Serial = CLKUART (SYNC Mode)
Board: MINI6410
DRAM: 256 MB
Flash: 0 kB
NAND: 2048 MB
In: serial
Out: serial
Err: serial
MAC: 08:90:90:90:90:90
下面代码的输出信息就可以在里面查得到
首先我们进入了uboot启动的第二阶段,主要做了哪些事呢:
1、初始化本阶段要使用到的硬件设备
2、检测系统内存映射
3、将内核映像和根文件系统映像从Flash上读到RAM空间中
4、为内核设置启动参数
5、调用内核
从下面的代码中,找到做这些事的地方吧!
/************************************************************************ * Init Utilities * ************************************************************************ * Some of this code should be moved into the core functions, * or dropped completely, * but let's get it working (again) first...初始化串口,设置波特率,这样就可以与uboot进行交互 */ static int init_baudrate (void) { char tmp[64]; /* long enough for environment variables */ int i = getenv_r ("baudrate", tmp, sizeof (tmp)); gd->bd->bi_baudrate = gd->baudrate = (i > 0) ? (int) simple_strtoul (tmp, NULL, 10) : CONFIG_BAUDRATE; return (0); } static int display_banner (void) { printf ("\n\n%s\n\n", version_string); debug ("U-Boot code: %08lX -> %08lX BSS: -> %08lX\n", _armboot_start, _bss_start, _bss_end); #ifdef CONFIG_MEMORY_UPPER_CODE /* by scsuh */ debug("\t\bMalloc and Stack is above the U-Boot Code.\n"); #else debug("\t\bMalloc and Stack is below the U-Boot Code.\n"); #endif #ifdef CONFIG_MODEM_SUPPORT debug ("Modem Support enabled\n"); #endif #ifdef CONFIG_USE_IRQ debug ("IRQ Stack: %08lx\n", IRQ_STACK_START); debug ("FIQ Stack: %08lx\n", FIQ_STACK_START); #endif return (0); } /* * WARNING: this code looks "cleaner" than the PowerPC version, but * has the disadvantage that you either get nothing, or everything. * On PowerPC, you might see "DRAM: " before the system hangs - which * gives a simple yet clear indication which part of the * initialization if failing. */ static int display_dram_config (void) { int i; ulong size = 0; /*只有一块ddr ram,大小为256M*/ for (i=0; i<CONFIG_NR_DRAM_BANKS; i++) { size += gd->bd->bi_dram[i].size; } puts("DRAM: "); print_size(size, "\n"); return (0); } #ifndef CFG_NO_FLASH static void display_flash_config (ulong size) { puts ("Flash: "); print_size (size, "\n"); } #endif /* CFG_NO_FLASH */ typedef int (init_fnc_t) (void); int print_cpuinfo (void); /* test-only */ /*这里是一系列的初始化,都放到一块,这可真方便*/ 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 */ console_init_f, /* stage 1 init of console */ display_banner, /* say that we are here */ #if defined(CONFIG_DISPLAY_CPUINFO) print_cpuinfo, /* display cpu info (and speed) */ #endif #if defined(CONFIG_DISPLAY_BOARDINFO) checkboard, /* display board info */ #endif dram_init, /* configure available RAM banks */ display_dram_config, NULL, }; //第二阶段程序入口 void start_armboot (void) { init_fnc_t **init_fnc_ptr; char *s; #ifndef CFG_NO_FLASH ulong size; #endif #if defined(CONFIG_VFD) || defined(CONFIG_LCD) unsigned long addr; #endif #if defined(CONFIG_BOOT_MOVINAND) uint *magic = (uint *) (PHYS_SDRAM_1); #endif /* Pointer is writable since we allocated a register for it */ #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)); monitor_flash_len = _bss_start - _armboot_start; for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) { if ((*init_fnc_ptr)() != 0) {/*逐一调用列表里面的每一个初始化函数*/ hang ();/*如果有一个出错就提示按reset键*/ } } #ifndef CFG_NO_FLASH /* configure available FLASH banks */ size = flash_init (); display_flash_config (size); #endif /* CFG_NO_FLASH */ /* 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) || \ defined(CONFIG_MINI6410) #if defined(CONFIG_NAND) puts ("NAND: "); nand_init(); /* go init the NAND */ NAND_Init(); #endif #if defined(CONFIG_ONENAND) puts ("OneNAND: "); onenand_init(); /* go init the One-NAND */ #endif #if defined(CONFIG_BOOT_MOVINAND) puts ("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 #ifdef CONFIG_HAS_DATAFLASH AT91F_DataflashInit(); dataflash_print_info(); #endif /* initialize environment */ env_relocate (); #ifdef CONFIG_VFD /* must do this after the framebuffer is allocated */ drv_vfd_init(); #endif /* CONFIG_VFD */ /* IP Address */ gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr"); /* MAC Address */ { int i; ulong reg; char *s, *e; char tmp[64]; i = getenv_r ("ethaddr", tmp, sizeof (tmp)); s = (i > 0) ? tmp : NULL; for (reg = 0; reg < 6; ++reg) { gd->bd->bi_enetaddr[reg] = s ? simple_strtoul (s, &e, 16) : 0; if (s) s = (*e) ? e + 1 : e; } #ifdef CONFIG_HAS_ETH1 i = getenv_r ("eth1addr", tmp, sizeof (tmp)); s = (i > 0) ? tmp : NULL; for (reg = 0; reg < 6; ++reg) { gd->bd->bi_enet1addr[reg] = s ? simple_strtoul (s, &e, 16) : 0; if (s) s = (*e) ? e + 1 : e; } #endif } devices_init (); /* get the devices list going. */ #ifdef CONFIG_CMC_PU2 load_sernum_ethaddr (); #endif /* CONFIG_CMC_PU2 */ jumptable_init (); console_init_r (); /* fully init console as a device */ #if defined(CONFIG_MISC_INIT_R) /* miscellaneous platform dependent initialisations */ misc_init_r (); #endif /* enable exceptions */ enable_interrupts (); /* Perform network card initialisation if necessary */ #if defined(CONFIG_DRIVER_DM9000) && defined(CONFIG_DRIVER_DM9000_NO_EEPROM) extern int eth_set_mac(bd_t * bd); if (getenv ("ethaddr")) { eth_set_mac(gd->bd); } #endif #ifdef CONFIG_DRIVER_CS8900 cs8900_get_enetaddr (gd->bd->bi_enetaddr); #endif #if defined(CONFIG_DRIVER_SMC91111) || defined (CONFIG_DRIVER_LAN91C96) if (getenv ("ethaddr")) { smc_set_mac_addr(gd->bd->bi_enetaddr); } #endif /* CONFIG_DRIVER_SMC91111 || CONFIG_DRIVER_LAN91C96 */ /* Initialize from environment */ if ((s = getenv ("loadaddr")) != NULL) { load_addr = simple_strtoul (s, NULL, 16); } #if (CONFIG_COMMANDS & CFG_CMD_NET) if ((s = getenv ("bootfile")) != NULL) { copy_filename (BootFile, s, sizeof (BootFile)); } #endif /* CFG_CMD_NET */ #ifdef BOARD_LATE_INIT board_late_init (); #endif #if (CONFIG_COMMANDS & CFG_CMD_NET) #if defined(CONFIG_NET_MULTI) puts ("Net: "); #endif eth_initialize(gd->bd); #endif /* main_loop() can return to retry autoboot, if so just run it again. */ for (;;) { main_loop (); /*当看到这里时,不禁大喜啊,可找到你了,想得你好苦啊!*/ } /* NOTREACHED - no way out of command loop except booting */ }转载请注明出处: http://blog.csdn.net/ecbtnrt/article/details/6630128