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 ("\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 */
}

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