以arm为例，文件位于lib_arm/board.c，主要分析start_armboot等相关函数
- global data数据结构定义，位于文件 include/asm-arm/global_data.h
#ifndef __ASM_GBL_DATA_H
#define __ASM_GBL_DATA_H
/*
* The following data structure is placed in some memory wich is
* available very early after boot (like DPRAM on MPC8xx/MPC82xx, or
* some locked parts of the data cache) to allow for a minimum set of
* global variables during system initialization (until we have set
* up the memory controller so that we can use RAM).
*
* Keep it *SMALL* and remember to set CFG_GBL_DATA_SIZE > sizeof(gd_t)
* CFG_GBL_DATA_SIZE在config文件中定义，start.S中会根据这个值分配栈空间给global_data，参见对start.S的分析stack_setup部分
*/
typedef struct global_data {
bd_t *bd; /* board info, 参见 include/asm-arm/u-boot.h */
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
unsigned long cpu_clk; /* CPU clock in Hz! */
unsigned long bus_clk;
unsigned long ram_size; /* RAM size */
unsigned long reset_status; /* reset status register at boot */
void **jt; /* jump table */
} gd_t;
/*
* Global Data Flags
*/
#define GD_FLG_RELOC 0x00001 /* Code was relocated to RAM */
#define GD_FLG_DEVINIT 0x00002 /* Devices have been initialized */
#define GD_FLG_SILENT 0x00004 /* Silent mode */
#define DECLARE_GLOBAL_DATA_PTR register volatile gd_t *gd asm ("r8") /* 定义gd为gd_t类型指针,存储在寄存器r8中 */
/* register:表示变量对于执行速度非常重要，因此应该放在机器的寄存器中（寄存器独立于内存，通常在处理器芯片上） */
/* volatile:用于指定变量的值可以由外部过程异步修改，例如中断例程 */
#endif /* __ASM_GBL_DATA_H */
- board info数据结构定义，位于文件 include/asm-arm/u-boot.h
#ifndef _U_BOOT_H_
#define _U_BOOT_H_ 1
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; /* environment struct */
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]; /* 每个DRAM bank的起始地址和大小，CONFIG_NR_DRAM_BANKS 定义DRAM的bank数 */
} bd_t;
#define bi_env_data bi_env->data
#define bi_env_crc bi_env->crc
#endif /* _U_BOOT_H_ */
/*
* All attempts to come up with a "common" initialization sequence
* that works for all boards and architectures failed: some of the
* requirements are just _too_ different. To get rid of the resulting
* mess of board dependent #ifdef'ed code we now make the whole
* initialization sequence configurable to the user.
*
* The requirements for any new initalization function is simple: it
* receives a pointer to the "global data" structure as it's only
* argument, and returns an integer return code, where 0 means
* "continue" and != 0 means "fatal error, hang the system".
*/
typedef int (init_fnc_t) (void);
init_fnc_t *init_sequence[] = {
cpu_init, /* basic cpu dependent setup */
init_baudrate, /* initialze baudrate settings */
serial_init, /* serial communications setup */
board_init, /* basic board dependent setup */
interrupt_init, /* set up exceptions */
env_init, /* initialize environment */
console_init_f, /* stage 1 init of console */
display_banner, /* say that we are here */
dram_init, /* configure available RAM banks */
display_dram_config,
#if defined(CONFIG_VCMA9) || defined (CONFIG_CMC_PU2)
checkboard,
#endif
NULL,
};
void start_armboot (void)
{
DECLARE_GLOBAL_DATA_PTR;
/* 声明全局数据指针 */ ulong size;
init_fnc_t **init_fnc_ptr;
/* init sequence */ char *s;
#if defined(CONFIG_VFD) || defined(CONFIG_LCD)
unsigned long addr;
#endif
/* Pointer is writable since we allocated a register for it */ ——
gd为gd_t类型指针,存储在寄存器r8中 gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t)); /* global data地址，栈空间分配参见start.S stack_setup部分 */
/* compiler optimization barrier needed for GCC >= 3.4 */
__asm__ __volatile__("": : :"memory");
/* 内联汇编语句__asm__("":::"memory")向GCC声明，在此内联汇编语句出现的位置内存内容可能改变了，
所以GCC在编译的时候，会将此因素考虑进去，而不会对代码进行优化及重新排序等操作,这样GCC会老老实实的生成汇编代码 */ memset ((void*)gd, 0, sizeof (gd_t));
gd->bd = (bd_t*)((char*)gd - sizeof(bd_t)); /* board info 地址*/
memset (gd->bd, 0, sizeof (bd_t));
monitor_flash_len = _bss_start - _armboot_start; /* .text段和.data段的总长 */
for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) { /* 按照initialization sequence进行初始化 */
if ((*init_fnc_ptr)() != 0) { /* where 0 means "continue" and != 0 means "fatal error, hang the system". */
hang ();
}
}
puts("Init flash...\n");
/* configure available FLASH banks */
size = flash_init (); /* init nor flash */
display_flash_config (size);
#ifdef CONFIG_VFD
# ifndef PAGE_SIZE
# define PAGE_SIZE 4096
# endif
/*
* reserve memory for VFD display (always full pages)
*/
/* bss_end is defined in the board-specific linker script， defined in start.S */
addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1); /* round up to nearest full page */
size = vfd_setmem (addr);
gd->fb_base = addr;
#endif /* CONFIG_VFD */
#ifdef CONFIG_LCD
# ifndef PAGE_SIZE
# define PAGE_SIZE 4096
# endif
/*
* reserve memory for LCD display (always full pages)
*/
/* bss_end is defined in the board-specific linker script */
addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
size = lcd_setmem (addr);
gd->fb_base = addr;
#endif /* CONFIG_LCD */
/* armboot_start is defined in the board-specific linker script */
mem_malloc_init (_armboot_start - CFG_MALLOC_LEN);
#if (CONFIG_COMMANDS & CFG_CMD_NAND)
puts ("NAND:");
nand_init(); /* go init the NAND */
#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;
uchar 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;
}
}
devices_init (); /* get the devices list going. */
#ifdef CONFIG_CMC_PU2
load_sernum_ethaddr ();
#endif /* CONFIG_CMC_PU2 */
jumptable_init (); /* init jump table */
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 */
#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); /* load address */
}
#if (CONFIG_COMMANDS & CFG_CMD_NET)
if ((s = getenv ("bootfile")) != NULL) {
copy_filename (BootFile, s, sizeof (BootFile)); /* net boot file */
}
#endif /* CFG_CMD_NET */
#ifdef BOARD_LATE_INIT
board_late_init (); /* init your board */
#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 ();
}
/* NOTREACHED - no way out of command loop except booting */
}
