u-boot第二阶段启动流程
u-boot 第一阶段启动流程:http://www.amobbs.com/thread-5595629-1-1.html详细请看：http://m18271260665.blog.163.com/
首先还是来一张图片大致看一下第二阶段完成的任务：
在第一阶段start.S的最后有这样一句代码：
ldr pc, _start_armboot @ jump to C code
当第一阶段的全部任务完成之后，就会调到_start_armboot 处开始执行第二阶段的代码，这里的_start_armboot 是一个标签，是函数void start_armboot (void)的首地址。这个函数在/lib_arm/board.c中。接下来就是按照上图中的步骤开始一步一步进行。
同样，board.c中，也用到了很多的条件编译，这里把没用编译的都去掉了，方便阅读，精简后的代码如下：
typedef struct environment_s {
uint32_t crc; /* CRC32 over data bytes */
unsigned char flags; /* active/obsolete flags */
unsigned char data; /* Environment data */
} env_t;
typedef struct bd_info {
//串口通讯波特率
int bi_baudrate; /* serial console baudrate */
//IP 地址
unsigned long bi_ip_addr; /* IP Address */
//环境变量起始地址
struct environment_s *bi_env;
//开发板的机器码
ulong bi_arch_number; /* unique id for this board */
//uboot传递给内核参数的起始地址
ulong bi_boot_params; /* where this board expects params */
//内存信息
struct /* RAM configuration */
{
ulong start;//内存的起始地址
ulong size;//内存大小
}bi_dram;
} bd_t;
typedef struct global_data {
bd_t *bd;
unsigned long flags; //uboot是否重定向的标志
//串口波特率
unsigned long baudrate;
//是否有一个控制台标志
unsigned long have_console; /* serial_init() was called */
//环境变量所在的地址
unsigned long env_addr; /* Addressof Environment struct */
//环境变量是否有效
unsigned long env_valid; /* Checksum of Environment valid? */
unsigned long fb_base; /* base address of frame buffer */
void **jt; /* jump table */
} gd_t;
typedef int (init_fnc_t) (void);
register volatile gd_t *gd asm ("r8");
ulong monitor_flash_len;
init_fnc_t *init_sequence[] = {
//初始化CPU相关设置:系统时钟操作函数
arch_cpu_init, /* basic arch cpu dependent setup */
//初始化开发板相关设置：开发板的机器码
board_init, /* basic board dependent setup */
//初始化定时器
timer_init, /* initialize timer */
//初始化环境变量
env_init, /* initialize environment */
//初始化波特率
init_baudrate, /* initialze baudrate settings */
//串口初始化
serial_init, /* serial communications setup */
//控制台设备一级初始化
console_init_f, /* stage 1 init of console */
//打印u-boot版本、编译时间
display_banner, /* say that we are here */
//打印CPU类型和当前运行频率
print_cpuinfo, /* display cpu info (and speed) */
//打印开发板名称
checkboard, /* display board info */
//配置可用的内存
dram_init, /* configure available RAM banks */
//显示当前内存大小
display_dram_config,
NULL,
};
void start_armboot (void)
{
init_fnc_t **init_fnc_ptr;
char *s;
/* Pointer is writable since we allocated a register for it
* _armboot_start :0x20f00044
* CONFIG_SYS_MALLOC_LEN:0x120000
* sizeof(gd_t) :0x40
*
* gd : 0x20de0004
*/
gd = (gd_t*)(_armboot_start - CONFIG_SYS_MALLOC_LEN - sizeof(gd_t));
/* compiler optimization barrier needed for GCC >= 3.4 */
__asm__ __volatile__("": : :"memory");
memset ((void*)gd, 0, sizeof (gd_t));
//gd->bd :0x20de0004 -0x38 = 0x20ddffcc
gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));
memset (gd->bd, 0, sizeof (bd_t));
gd->flags |= GD_FLG_RELOC;
//uboot去掉bss段的大小
monitor_flash_len = _bss_start - _armboot_start;
//外围硬件初始化
for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {
if ((*init_fnc_ptr)() != 0) {
hang ();
}
}
//将堆区初始化为0
/* armboot_start is defined in the board-specific linker script */
mem_malloc_init (_armboot_start - CONFIG_SYS_MALLOC_LEN,
CONFIG_SYS_MALLOC_LEN);
puts ("NAND:");
//NAND FALSH 初始化
nand_init(); /* go init the NAND */
/*读取Nand Flash的环境变量，然后做CRC校验,如果错误则使用默认的环境变量*/
env_relocate ();
/*获得IP 地址*/
gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr");
//初始化输入、输出设备列表
stdio_init (); /* get the devices list going. */
jumptable_init ();
//初始化标准输入、输出、出错
console_init_r (); /* fully init console as a device */
/* 使能IRQ异常 */
enable_interrupts ();
/* Initialize from environment */
if ((s = getenv ("loadaddr")) != NULL) {
load_addr = simple_strtoul (s, NULL, 16);
}
//初始化网卡设备
eth_initialize(gd->bd);
/* 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 */
}
void hang (void)
{
puts ("### ERROR ### Please RESET the board ###\n");
for (;;);
}
相关的初始化完成之后，会进入到main_loop ();
void main_loop (void)
{
char *s;
int bootdelay;
u_boot_hush_start ();
s = getenv ("bootdelay");
bootdelay = s ? (int)simple_strtol(s, NULL, 10) : CONFIG_BOOTDELAY;
debug ("### main_loop entered: bootdelay=%d\n\n", bootdelay);
s = getenv ("bootcmd");
debug ("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");
if (bootdelay >= 0 && s && !abortboot (bootdelay)) {
parse_string_outer(s, FLAG_PARSE_SEMICOLON |
FLAG_EXIT_FROM_LOOP);
/*
* Main Loop for Monitor Command Processing
*/
parse_file_outer();
/* This point is never reached */
for (;;);
}
static __inline__ int abortboot(int bootdelay)
{
int abort = 0;
printf("Hit any key to stop autoboot: %2d ", bootdelay);
/*
* Check if key already pressed
* Don't check if bootdelay < 0
*/
if (bootdelay >= 0) {
if (tstc()) { /* we got a key press */
(void) getc();/* consume input */
puts ("\b\b\b 0");
abort = 1; /* don't auto boot */
}
}
while ((bootdelay > 0) && (!abort)) {
int i;
--bootdelay;
/* delay 100 * 10ms */
for (i=0; !abort && i<100; ++i) {
if (tstc()) { /* we got a key press */
abort= 1; /* don't auto boot */
bootdelay = 0; /* no more delay */
(void) getc();/* consume input */
break;
}
udelay(10000);
}
printf("\b\b\b%2d ", bootdelay);
}
putc('\n');
return abort;
}
最后bootcmd这条命令设置为引导内核气动就OK了。。。
u-boot 第一阶段启动流程:http://www.amobbs.com/thread-5595629-1-1.html
详细请看：http://m18271260665.blog.163.com/
谢谢分享，讲的真详细 还不错哦 图文并茂，把整个流程都很清楚画出来了，容易看懂。谢谢！ 讲的真详细，谢谢 学习一下 很详细，正在读 大哥，出个PDF的文档吧，，方便收藏。。{:lol:}{:lol:}{:lol:} 不错，呵呵。 多谢了楼主共享啊，赞。。。 感谢楼主分享 多谢分享……
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