uboot源码阅读（四）江湖的面纱 uboot第二阶段

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 ("nn%snn",version_string);
	debug ("U-Boot code: %08lX -> %08lX  BSS: -> %08lXn",_armboot_start,_bss_start,_bss_end);
#ifdef CONFIG_MEMORY_UPPER_CODE /* by scsuh */
	debug("tbMalloc and Stack is above the U-Boot Code.n");
#else
	debug("tbMalloc and Stack is below the U-Boot Code.n");
#endif
#ifdef CONFIG_MODEM_SUPPORT
	debug ("Modem Support enabledn");
#endif
#ifdef CONFIG_USE_IRQ
	debug ("IRQ Stack: %08lxn",IRQ_STACK_START);
	debug ("FIQ Stack: %08lxn",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,};
//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,sizeof (gd_t));
	gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));
	memset (gd->bd,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 burningn");
	} 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",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",sizeof (tmp));
		s = (i > 0) ? tmp : NULL;

		for (reg = 0; reg < 6; ++reg) {
			gd->bd->bi_enet1addr[reg] = s ? simple_strtoul (s,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,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 */
}