u-boot 1.1.6 第二阶段引导

在uboot第一阶段引导的最后一步做了一下代码

ldr	pc, _start_armboot
33f800f0:	e51ff004 ldr	pc, [pc, #-4]	; 33f800f4 <_start_armboot>
33f800f4 <_start_armboot>:
33f800f4:	33f80be0 mvnccs	r0, #229376	; 0x38000

该指令是把当前指令地址+4的内存地址的值赋值为PC，PC=0x33f80be0；

第一阶段的代码是地址无关代码，但是现在PC却指向了0x33f80be0处，此处的代码在uboot(1.1.6)的根目录下/lib_arm/board.c中的start_armboot函数，主要是一些初始化。其中关系到两个数据结构

typedef	struct	global_data {
bd_t		*bd;
unsigned long	flags;
unsigned long	baudrate;
unsigned long	have_console;		/* serial_init() was called */
unsigned long	reloc_off;		/* Relocation Offset */
unsigned long	env_addr;		/* Address  of Environment struct */
unsigned long	env_valid;		/* Checksum of Environment valid? */
unsigned long	fb_base;			/* base address of frame buffer */
#ifdef CONFIG_VFD
unsigned char	vfd_type;		/* display type */
#endif
void		**jt;				/* jump table */
} gd_t;

 #define DECLARE_GLOBAL_DATA_PTR     register volatile gd_t *gd asm ("r8")

gd指针的值存放在r8寄存器里，register是将gd指针和r8绑定在一起，volatile关键字的意思是每次使用该变量时都直接存取原始地址，和内核中的task_struct结构中的state变量一样

typedef struct bd_info {
int			bi_baudrate;			/* serial console baudrate */
unsigned long	bi_ip_addr;		/* IP Address */
unsigned char	bi_enetaddr[6]; 	/* Ethernet adress */
struct environment_s	       *bi_env;
ulong	        bi_arch_number;			/* unique id for this board */
ulong	        bi_boot_params;			/* where this board expects params */
struct					/* RAM configuration */
{
ulong start;
ulong size;
} 			bi_dram[CONFIG_NR_DRAM_BANKS];

#ifdef CONFIG_HAS_ETH1
/* second onboard ethernet port */
unsigned char   bi_enet1addr[6];
#endif
} bd_t;

在start_armboot函数里先是gd的初始化然后再进行系统初始化，在2011.03版本中这两部分的初始化是放在两个函数里，而且gd的初始化是在relocate_code之前进行的。

gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));

从这里可以发现gd的数据在内存里存放的地址是位于uboot代码和malloc区域的上方，由于传统栈的生长方向满递减，所以gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));

接下来是把初始化队列里的函数按顺序执行下来，如果执行错误，则执行hang()，实际是死循环。

接着是flash的初始化，

malloc区域的初始化，

uboot的环境的初始化先是在malloc区域申请指定大小的内存，再是初始化，并设置好gd结构里相应的标志位，和该区域的地址，

#ifdef ENV_IS_EMBEDDED
/*
* The environment buffer is embedded with the text segment,
* just relocate the environment pointer
*/
env_ptr = (env_t *)((ulong)env_ptr + gd->reloc_off);
DEBUGF ("%s[%d] embedded ENV at %p\n", __FUNCTION__,__LINE__,env_ptr);
#else
/*
* We must allocate a buffer for the environment
*/
env_ptr = (env_t *)malloc (CFG_ENV_SIZE);
DEBUGF ("%s[%d] malloced ENV at %p\n", __FUNCTION__,__LINE__,env_ptr);
#endif
......
......
memset (env_ptr, 0, sizeof(env_t));
memcpy (env_ptr->data,
.....
gd->env_valid = 1;
......
gd->env_addr = (ulong)&(env_ptr->data);

ip地址的配置并将地址放到gd结构里等网卡的初始化时再去读取，

初始化板子上有的设备，例如usb，keyboard，lcd等，

/* Initialize the list */
devlist = ListCreate (sizeof (device_t));

if (devlist == NULL) {
eputs ("Cannot initialize the list of devices!\n");
return -1;
}
#if defined(CONFIG_HARD_I2C) || defined(CONFIG_SOFT_I2C)
i2c_init (CFG_I2C_SPEED, CFG_I2C_SLAVE);
#endif
......
......
return (0);

填充jumptable里的数据

gd->jt[XF_get_version] = (void *) get_version;
gd->jt[XF_malloc] = (void *) malloc;
gd->jt[XF_free] = (void *) free;
gd->jt[XF_getenv] = (void *) getenv;
gd->jt[XF_setenv] = (void *) setenv;
gd->jt[XF_get_timer] = (void *) get_timer;
gd->jt[XF_simple_strtoul] = (void *) simple_strtoul;
gd->jt[XF_udelay] = (void *) udelay;
#if defined(CONFIG_I386) || defined(CONFIG_PPC)
gd->jt[XF_install_hdlr] = (void *) irq_install_handler;
gd->jt[XF_free_hdlr] = (void *) irq_free_handler;
#endif	/* I386 || PPC */
#if (CONFIG_COMMANDS & CFG_CMD_I2C)
gd->jt[XF_i2c_write] = (void *) i2c_write;
gd->jt[XF_i2c_read] = (void *) i2c_read;
#endif	/* CFG_CMD_I2C */

再就是控制台的初始化，开启中断，初始化相应的网卡，最后进入了main_loop。