程序从start。S开始启动
start_code:
?/*
? * set the cpu to SVC32 mode? 设置管理模式
? */
?mrs?r0,cpsr???????
?bic?r0,r0,#0x1f??????
?orr?r0,#0xd3
?msr?cpsr,r0
#ifdef CONFIG_S3C24X0
?/* turn off the watchdog */
/*关看门狗 关中断*/
# if defined(CONFIG_S3C2400)
#? define pWTCON?0x15300000
#? define INTMSK?0x14400008?/* Interupt-Controller base addresses */
#? define CLKDIVN?0x14800014?/* clock divisor register */
#else
#? define pWTCON?0x53000000
#? define INTMSK?0x4A000008?/* Interupt-Controller base addresses */
#? define INTSUBMSK?0x4A00001C
#? define CLKDIVN?0x4C000014?/* clock divisor register */
# endif
?ldr?r0,=pWTCON
?mov?r1,#0x0
?str?r1,[r0]
?/*
? * mask all IRQs by setting all bits in the INTMR - default
? */
?mov?r1,#0xffffffff
?ldr?r0,=INTMSK
?str?r1,[r0]
# if defined(CONFIG_S3C2410)??? //shut up all interrupt
?ldr?r1,=0x3ff
?ldr?r0,=INTSUBMSK
?str?r1,[r0]
# endif
?/* FCLK:HCLK:PCLK = 1:2:4 */
?/* default FCLK is 120 MHz ! */
?ldr?r0,=CLKDIVN
?mov?r1,#3
?str?r1,[r0]
#endif?/* CONFIG_S3C24X0 */
#ifndef CONFIG_SKIP_LOWLEVEL_INIT
?bl?cpu_init_crit????????? #跳转到cpu_init_crit处 对CPU的cashe mmu进行初始化 关闭
#endif
#ifndef CONFIG_SKIP_RELOCATE_UBOOT
relocate:????/* relocate U-Boot to RAM???? */#加载uboot到RAM对于nor flash 启动boot//本可以直接运行但是效率低所以加载到RAM中运行
?adr?r0,_start??/* r0 <- current position of code?? */?? #加载运行起始地址到r0? 如果从nor flash启动 这里为0x0
?ldr?r1,_TEXT_BASE??/* test if we run from flash or RAM */ #加载_TEXT_BASE到r1 _TEXT_BASE位于SDRAM中??默认为0x33f80000
?cmp?r0,r1???/* don't reloc during debug???????? */????? #比较r0 与 r1 即判断程序是从flash启动还是从RAM启动
?beq?stack_setup?? /*如果r0 == r1 就跳转到stack_up*/???????? #如果相等 表示从RAM启动 那么下面的代码搬运到RAM步骤就没比要了 直接跳到stack_setup运行
?ldr?r2,_armboot_start?????????? #代码搬运
?ldr?r3,_bss_start?????? /*U-boot.lds中定义 uboot代码的结束地址*/
?sub?r2,r3,r2??/* r2 <- size of armboot??????????? */?? #得到代码长度
?add?r2,r2??/* r2 <- source end address???????? */? #r2中存放uboot结束代码地址
copy_loop:???????????????????? /*将数据从norflash搬到SDRAM r0为_start程序开始地址r1为_TEXT_BASE属于SDRAM中的地址0x33f80000 所以我们的uboot 512KB*/
?ldmia?r0!,{r3-r10}??/* copy from source address [r0]??? */? #从起始地址开始搬_start
?stmia?r1!,{r3-r10}??/* copy to?? target address [r1]??? */????? #搬到目的地址 从_TEXT_BASE开始
?cmp?r0,r2???/* until source end addreee [r2]??? */???????????? #判断是否搬完 即r0中的值是否==上面r2中值
?ble?copy_loop
#endif?/* CONFIG_SKIP_RELOCATE_UBOOT */
?/* Set up the stack????????? */
stack_setup:??????????????????????????????????????????????????? #搬完了后设置栈? 前面说的判断程序启动地址 如果从RAM启动 则直接来设置栈，有栈了后才能使用c语言。。。
?ldr?r0,_TEXT_BASE??/* upper 128 KiB: relocated uboot?? */?? #栈为向下生长 在确定栈指针sp之前? 先留出部分空间?放下面的内容
?sub?r0,#CONFIG_SYS_MALLOC_LEN?/* malloc area????????????? */??? #1? 一段长度放置malloc段
?sub?r0,#CONFIG_SYS_GBL_DATA_SIZE /* bdinfo???????????????? */????? #2? 一段长度放置GBL段
#ifdef CONFIG_USE_IRQ
?sub?r0,#(CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ)?? #3 还要留一段长度放置IRQ FIQ中断状态保存段
#endif
?sub?sp,#12??/* leave 3 words for abort-stack??? */
?bic?sp,sp,#7??/* 8-byte alignment for ABI compliance */??????????????? #接下来就是sp指针的位置了
clear_bss:?????????????????????????????????????????????????????????????????????????????????????????????? #做完了后在开始跳到uboot第二阶段的C代码前?清BSS段 这里放了一些初始化为0的或者没有初始化的全局?#????? 变????????? 量??? 局部变量? 可以先清掉 在当要调用的时候再赋值
?ldr?r0,_bss_start??/* find start of bss segment??????? */
?ldr?r1,_bss_end??/* stop here??????????????????????? */
?mov?r2,#0x00000000??/* clear??????????????????????????? */???? #全部清空
clbss_l:str?r2,[r0]??/* clear loop...??????????????????? */
?add?r0,#4
?cmp?r0,r1
?ble?clbss_l
?ldr?pc,_start_armboot???????????????????????????????????????? #将指针指向_start_armboot? 这里为第二阶段C函数的入口了
_start_armboot:?.word start_armboot
?
void start_armboot (void)
{
?init_fnc_t **init_fnc_ptr;
?char *s;
#if defined(CONFIG_VFD) || defined(CONFIG_LCD)
?unsigned long addr;
#endif
?/* Pointer is writable since we allocated a register for it */
?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,sizeof (gd_t));
?gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));
?memset (gd->bd,sizeof (bd_t));
?gd->flags |= GD_FLG_RELOC;
?monitor_flash_len = _bss_start - _armboot_start;
?for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {??????????????????????? //这里为调用一系列初始化函数? 具体见uboot源码，就是初始化各个外设模块 串口啊 GPIO USB
??if ((*init_fnc_ptr)() != 0) {
???hang ();
??}
?}
?/* armboot_start is defined in the board-specific linker script */
?mem_malloc_init (_armboot_start - CONFIG_SYS_MALLOC_LEN,
???CONFIG_SYS_MALLOC_LEN);
#ifndef CONFIG_SYS_NO_FLASH
?/* configure available FLASH banks */
?display_flash_config (flash_init ());
#endif /* CONFIG_SYS_NO_FLASH */
#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 */
?addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
?vfd_setmem (addr);
?gd->fb_base = addr;
#endif /* CONFIG_VFD */
#ifdef CONFIG_LCD
?/* board init may have inited fb_base */
?if (!gd->fb_base) {
#??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);
??lcd_setmem (addr);
??gd->fb_base = addr;
?}
#endif /* CONFIG_LCD */
#if defined(CONFIG_CMD_NAND)
?puts ("NAND:? ");
?nand_init();??/* go init the NAND */
#endif
#if defined(CONFIG_CMD_ONENAND)
?onenand_init();
#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 */
#ifdef CONFIG_SERIAL_MULTI
?serial_initialize();
#endif
?/* IP Address */
?gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr");
?stdio_init ();?/* get the devices list going. */
?jumptable_init ();
#if defined(CONFIG_API)
?/* Initialize API */
?api_init ();
#endif
?console_init_r ();?/* fully init console as a device */
#if defined(CONFIG_ARCH_MISC_INIT)
?/* miscellaneous arch dependent initialisations */
?arch_misc_init ();
#endif
#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_TI_EMAC
?/* XXX: this needs to be moved to board init */
extern void davinci_eth_set_mac_addr (const u_int8_t *addr);
?if (getenv ("ethaddr")) {
??uchar enetaddr[6];
??eth_getenv_enetaddr("ethaddr",enetaddr);
??davinci_eth_set_mac_addr(enetaddr);
?}
#endif
#if defined(CONFIG_DRIVER_SMC91111) || defined (CONFIG_DRIVER_LAN91C96)
?/* XXX: this needs to be moved to board init */
?if (getenv ("ethaddr")) {
??uchar enetaddr[6];
??eth_getenv_enetaddr("ethaddr",enetaddr);
??smc_set_mac_addr(enetaddr);
?}
#endif /* CONFIG_DRIVER_SMC91111 || CONFIG_DRIVER_LAN91C96 */
?/* Initialize from environment */
?if ((s = getenv ("loadaddr")) != NULL) {
??load_addr = simple_strtoul (s,NULL,16);
?}
#if defined(CONFIG_CMD_NET)
?if ((s = getenv ("bootfile")) != NULL) {
??copy_filename (BootFile,s,sizeof (BootFile));
?}
#endif
#ifdef BOARD_LATE_INIT
?board_late_init ();
#endif
#ifdef CONFIG_GENERIC_MMC
?puts ("MMC:?? ");
?mmc_initialize (gd->bd);
#endif
#ifdef CONFIG_BITBANGMII
?bb_miiphy_init();
#endif
#if defined(CONFIG_CMD_NET)
#if defined(CONFIG_NET_MULTI)
?puts ("Net:?? ");
#endif
?eth_initialize(gd->bd);
#if defined(CONFIG_RESET_PHY_R)
?debug ("Reset Ethernet PHYn");
?reset_phy();
#endif
#endif
?/* main_loop() can return to retry autoboot,if so just run it again. */
?for (;;) {
??main_loop ();?????????????????????//上面各个板级外设初始化完成后 开始进入main_loop()死循环
?}
?/* NOTREACHED - no way out of command loop except booting */
}
void main_loop (void)
s = getenv ("bootdelay");
?bootdelay = s ? (int)simple_strtol(s,10) : CONFIG_BOOTDELAY;??????? //如果定义了延时 加载这条? 这里涉及一个重要的函数getenv()获得环境变量
run_command (s,0);?????? //死循环中运行命令函数? 我们在串口输入各种命令 就是靠这个函数解析
