arm920t架构的，所以去分析cpu/arm920t/start.S源文件。
# U-Boot objects....order is important (i.e. start must be first)
OBJS = cpu/$(CPU)/start.o
OBJS := $(addprefix $(obj),$(OBJS))
(2)start_code: /* set the cpu to SVC32 mode*/
/* turn off the watchdog */
/* mask all IRQs by setting all bits in the INTMR - default */
/* setup FCLK:HCLK:PCLK */
blcpu_init_crit /*do sys-critical inits only at reboot*/
#ifndef CONFIG_SKIP_RELOCATE_UBOOT
/* relocate U-Boot from nor flash to RAM */
/* Set up the stack */
/* Clear bss */
/* jump to second stage */
ldrpc, _start_armboot
_start_armboot:.word start_armboot
typedef int (init_fnc_t) (void);
init_fnc_t *init_sequence[] = {
#if defined(CONFIG_ARCH_CPU_INIT)
arch_cpu_init,/* basic arch cpu dependent setup */
#endif
board_init,
/* basic board dependent setup */
#if defined(CONFIG_USE_IRQ)
interrupt_init,/* set up exceptions */
#endif
timer_init,
/* initialize timer */
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
#if defined(CONFIG_HARD_I2C) || defined(CONFIG_SOFT_I2C)
init_func_i2c,
#endif
dram_init,
/* configure available RAM banks */
#if defined(CONFIG_CMD_PCI) || defined (CONFIG_PCI)
arm_pci_init,
#endif
display_dram_config,
NULL,
};
for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {
if ((*init_fnc_ptr)() != 0) {
hang ();
}
}，通过一个for循环来依次访问函数指针数组init_sequence中的成员函数，进一步完成相关初始化和相关设置。
nand_init();
/* go init the NAND */，初始化nand flash。
serial_initialize(); ，初始化串口。
/* main_loop() can return to retry autoboot, if so just run it again. */
for (;;) {
main_loop ();
}
/* NOTREACHED - no way out of command loop except booting */，在无限for循环内，执行main_loop函数。
4.4：分析/common/main.c里的main_loop函数：处理uboot命令。
/*
* Main Loop for Monitor Command Processing
*/
for(;;){
#ifdef CONFIG_BOOT_RETRY_TIME
if (rc >= 0) {
/* Saw enough of a valid command to
* restart the timeout.
*/
reset_cmd_timeout();
}
#endif
len = readline (CONFIG_SYS_PROMPT);
flag = 0;
/* assume no special flags for now */
if (len > 0)
strcpy (lastcommand, console_buffer);
else if (len == 0)
flag |= CMD_FLAG_REPEAT;
#ifdef CONFIG_BOOT_RETRY_TIME
else if (len == -2) {
/* -2 means timed out, retry autoboot
*/
puts ("\nTimed out waiting for command\n");
# ifdef CONFIG_RESET_TO_RETRY
/* Reinit board to run initialization code again */
do_reset (NULL, 0, 0, NULL);
# else
return;
/* retry autoboot */
# endif
}
#endif
U_BOOT_CMD(
bootm,
CONFIG_SYS_MAXARGS,1,do_bootm,
"boot application image from memory",
"[addr [arg ...]]\n - boot application image stored in memory\n"
"\tpassing arguments ‘arg ...‘; when booting a Linux kernel,\n"
"\t‘arg‘ can be the address of an initrd image\n"
"\tbdt - OS specific bd_t processing\n"
"\tcmdline - OS specific command line processing/setup\n"
"\tprep - OS specific prep before relocation or go\n"
"\tgo - start OS"
);
