uboot 启动流程分析.doc

U-Boot启动流程大多数bootloader都分为stage1和stage2两大部分，u-boot也不例外。依赖于CPU体系结构的代码(如设备初始化代码等) 通常都放在stage1，且可以用汇编语言来实现，而stage2则通常用C语言来实现，这样可以实现复杂的功能，而且有更好的可读性和移植性。u-boot启动大致流程如图1所示： 图 1 Stage1在flash中执行的引导代码,也就是bootloader中的stage1,负责初始化硬件环境，把u-boot从flash加载到RAM中去，然后跳到lib_arm/board.c中的start_armboot中去执行。u-boot的stage1代码通常放在start.s文件中，它用汇编语言写成，其主要代码部分如下：1)定义入口由于一个可执行的Image必须有一个入口点，并且只能有一个全局入口，通常这个入口放在ROM(Flash) 的0x0地址，因此，必须通知编译器以使其知道这个入口，该工作可通过修改连接器脚本来完成。2)设置异常向量(Exception Vector) 。3)设置CPU的速度、时钟频率及中断控制寄存器。4)初始化内存控制器5)将ROM中的程序复制到RAM中。6)初始化堆栈7)转到RAM中执行，该工作可使用指令ldr pc, _start_armboot来完成。 Stage2lib_arm/board.c中的start_armboot是C语言开始的函数，也是整个启动代码中C语言的主函数，同时还是整个u-boot(armboot) 的主函数，该函数主要流程分析如下：void start_armboot (void) init_fnc_t *init_fnc_ptr; char *s;#if !defined(CFG_NO_FLASH) | defined (CONFIG_VFD) | defined(CONFIG_LCD) ulong size;#endif#if defined(CONFIG_VFD) | defined(CONFIG_LCD) unsigned long addr;#endif /* Pointer is writable since we allocated a register for it */ /* 给全局数据变量gd安排空间 */ gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t); /* compiler optimization barrier needed for GCC = 3.4 */ _asm_ _volatile_(: : :memory); /* 给板子数据变量gd-bd安排空间 */ memset (void*)gd, 0, sizeof (gd_t); gd-bd = (bd_t*)(char*)gd - sizeof(bd_t); memset (gd-bd, 0, sizeof (bd_t); monitor_flash_len = _bss_start - _armboot_start; /* 顺序执行init_sequence数组中的初始化函数 */ for (init_fnc_ptr = init_sequence; *init_fnc_ptr; +init_fnc_ptr) if (*init_fnc_ptr)() != 0) hang (); /*初始化函数列表： init_fnc_t *init_sequence = cpu_init, /* basic cpu dependent setup */#if defined(CONFIG_SKIP_RELOCATE_UBOOT) reloc_init, /* Set the relocation done flag, must do this AFTER cpu_init(), but as soon as possible */#endif board_init, /* basic board dependent setup */ interrupt_init, /* set up exceptions */ 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_HW_WATCHDOG) hw_watchdog_init, /* watchdog setup */#endif#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 */ display_dram_config, NULL,; */ /* armboot_start is defined in the board-specific linker script */ mem_malloc_init (_armboot_start - CFG_MALLOC_LEN);#if defined(CONFIG_CMD_NAND) puts (NAND: ); /* NAND FLASH初始化 */ nand_init(); /* go init the NAND */#endif /* 重新定位环境变量 */ env_relocate ();#ifdef CONFIG_VFD /* must do this after the framebuffer is allocated */ drv_vfd_init();#endif /* CONFIG_VFD */#ifdef CONFIG_SERIAL_MULTI /* 串口初始化 */ serial_initialize();#endif /* 从环境变量中获取IP地址和MAC地址 */ gd-bd-bi_ip_addr = getenv_IPaddr (ipaddr); /* MAC Address */ int i; ulong reg; char *s, *e; char tmp64; i = getenv_r (ethaddr, tmp, sizeof (tmp); s = (i 0) ? tmp : NULL; for (reg = 0; reg bd-bi_enetaddrreg = s ? simple_strtoul (s, &e, 16) : 0; if (s) s = (*e) ? e + 1 : e; #ifdef CONFIG_HAS_ETH1 i = getenv_r (eth1addr, tmp, sizeof (tmp); s = (i 0) ? tmp : NULL; for (reg = 0; reg bd-bi_enet1addrreg = s ? simple_strtoul (s, &e, 16) : 0; if (s) s = (*e) ? e + 1 : e; #endif devices_init (); /* get the devices list going. */#ifdef CONFIG_CMC_PU2 load_sernum_ethaddr ();#endif /* CONFIG_CMC_PU2 */ /* 跳转表的初始化*/ jumptable_init (); /* 控制台的初始化 */ console_init_r (); /* fully init console as a device */ /* IRQ中断使能 */ enable_interrupts (); /* 各种型号网络设备的初始化 */#ifdef CONFIG_DRIVER_TI_EMACextern void dm644x_eth_set_mac_addr (const u_int8_t *addr); if (getenv (ethaddr) dm644x_eth_set_mac_addr(gd-bd-bi_enetaddr); #endif#ifdef CONFIG_DRIVER_CS8900 cs8900_get_enetaddr (gd-bd-bi_enetaddr);#endif /* 通过环境变量初始化load_addr 默认定义ulong load_addr = CFG_LOAD_ADDR; */ 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#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 /* 循环不断地执行main_loop ()函数main_loop ()主要处理用户命令 */ for (;) main_loop (); 整个u-boot的执行就进入等待用户输入命令，解析并执行命令的死循环中。也许细心的你会问：我在用UBoot的时候并没有直接进入用户命令界面呀，而是在倒计时结束后自动引导kernel。这是怎么回事呢？在 main_loop（）函数当中有如下一段代码：#if defined(CONFIG_BOOTDELAY) & (CONFIG_BOOTDELAY = 0) s = getenv (bootcmd); /*获取bootcmd 的内容*/ /*bootcmd=nand read 0x22000000 0xB0000 0x200000; bootm */ # ifndef CFG_HUSH_PARSER run_command (s, 0); /*运行s包含的命令*/ /*运行nand read 0x22000000 0xB0000 0x200000表示将NANDFLASH 0xB0000处数据读取放于0x22000000处，读取长度为0x200000 */ /*运行bootm命令，引导内核启动*/# else parse_string_outer(s, FLAG_PARSE_SEMICOLON | FLAG_EXIT_FROM_LOOP);# endif #endif /* CONFIG_BOOTDELAY */bootm命令是什么？它是怎样引导内核的？要知道想解决这个问题，就要分析common/cmd_bootm.c中的函数do_bootm，因为引导kernel就是bootm这条命令的工作，do_bootm是命令bootm的执行函数。现在我们来分析一下common/cmd_bootm.c中的函数do_bootm，这是bootm命令的处理函数。int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char *argv) ulong iflag; const char *type_name; uint unc_len = CFG_BOOTM_LEN; uint8_t comp, type, os; void *os_hdr; ulong os_data, os_len; ulong image_start, image_end; ulong load_start, load_end; ulong mem_start; phys_size_t mem_size; struct lmb lmb; memset (void *)&images, 0, sizeof (images); images.verify = getenv_yesno (verify); images.lmb = &lmb; lmb_init(&lmb); mem_start = getenv_bootm_low(); mem_size = getenv_bootm_size(); lmb_add(&lmb, (phys_addr_t)mem_start, mem_size); board_lmb_reserve(&lmb); /* get kernel image header, start address and length */ /* 获取内核镜像头信息 */ /* 打印 “# Booting kernel from Legacy Image at 22000000 . Image Name: Linux-2.6.30 Image Type: ARM Linux Kernel Image (uncompressed) Data Size: 1507760 Bytes = 1.4 MB Load Address: 20008000 Entry Point: 20008000 Verifying Checksum . OK”*/ os_hdr = boot_get_kernel (cmdtp, flag, argc, argv, &images, &os_data, &os_len); if (os_len = 0) puts (ERROR: cant get kernel image!n); return 1; /* get image parameters */ /* 获取内核镜像格式 */ switch (genimg_get_format (os_hdr) case IMAGE_FORMAT_LEGACY: /* 获取内核镜像参数 */ type = image_get_type (os_hdr); comp = image_get_comp (os_hdr); os = image_get_os (os_hdr); image_end = image_get_image_end (os_hdr); load_start = image_get_load (os_hdr); break; image_start = (ulong)os_hdr; load_end = 0; type_name = genimg_get_type_name (type); /* 禁止所有中断 */ iflag = disable_interrupts();#ifdef CONFIG_AMIGAONEG3SE /* * Weve possible left the caches enabled during * bios emulation, so turn them off again */ icache_disable(); invalidate_l1_instruction_cache(); flush_data_cache(); dcache_disable();#endif switch (comp) case IH_COMP_NONE: /* 加载内核镜像 */ /* 打印“Loading Kernel Image . OK” */ if (load_start = (ulong)os_hdr) printf ( XIP %s . , type_name); else printf ( Loading %s . , type_name); memmove_wd (void *)load_start, (void *)os_data, os_len, CHUNKSZ); load_end = load_start + os_len; puts(OKn); break; puts (OKn); debug ( kernel loaded at 0x%08lx, end = 0x%08lxn, load_start, load_end); show_boot_progress (7); /* 加载错误 */ if (load_start image_start) debug (image_start = 0x%lX, image_end = 0x%lxn, image_start, image_end); debug (load_start = 0x%lx, load_end = 0x%lxn, load_start, load_end); if (images.legacy_hdr_valid) if (image_get_type (&images.legacy_hdr_os_copy) = IH_TYPE_MULTI) puts (WARNING: legacy format multi component image overwrittenn); else puts (ERROR: new format image overwritten - must RESET the board to recovern); show_boot_progress (-113); do_reset (cmdtp, flag, argc, argv); show_boot_progress (8); lmb_reserve(&lmb, load_start, (load_end - load_start); switch (os) default: /* handled by (original) Linux case */ case IH_OS_LINUX:#ifdef CONFIG_SILENT_CONSOLE fixup_silent_linux();#endif /* 引导内核启动函数 */ do_bootm_linux (cmdtp, flag, argc, argv, &images); break; show_boot_progress (-9);#ifdef DEBUG puts (n# Control returned to monitor - resetting.n); do_reset (cmdtp, flag, argc, argv);#endif if (iflag) enable_interrupts(); return 1;至此do_bootm函数完成引导内核前的准备任务了。引导内核启动函数将由do_bootm_linux()函数执行。do_bootm_linux()函数位于lib_arm/Bootm.c文件中，主要流程分析如下：void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv, bootm_headers_t *images) ulong initrd_start, initrd_end; ulong ep = 0; bd_t *bd = gd-bd; char *s; int machid = bd-bi_arch_number; void (*theKernel)(int zero, int arch, uint params); int ret;#ifdef CONFIG_CMDLINE_TAG char *commandline = getenv (bootargs);#endif /* find kernel entry point */ if (images-legacy_hdr_valid) ep = image_get_ep (&images-legacy_hdr_os_copy);#if defined(CONFIG_FIT) else if (images-fit_uname_os) ret = fit_image_get_entry (images-fit_hdr_os, images-fit_noffset_os, &ep); if (ret) puts (Cant get entry point property!n); goto error; #endif else puts (Could not find kernel entry point!n); goto error; theKernel = (void (*)(int, int, uint)ep; s = getenv (machid); if (s) machid = simple_strtoul (s, NULL, 16); printf (Using machid 0x%x from environmentn, machid); ret = boot_get_ramdisk (argc, argv, images, IH_ARCH_ARM, &initrd_start, &initrd_end); if (ret) goto error; show_boot_progress (15); debug (# Transferring control to Linux (at address %08lx) .n, (ulong) theKernel);#if defined (CONFIG_SETUP_MEMORY_TAGS) | defined (CONFIG_CMDLINE_TAG) | defined (CONFIG_INITRD_TAG) | defined (CONFIG_SERIAL_TAG) | defined (CONFIG_REVISION_TAG) | defined (CONFIG_LCD) | defined (CONFIG