U-Boot启动引导内核分析(二).doc

U-Boot启动引导内核分析(二) 2011-03-23 09:20:00| 分类： 默认分类 | 标签： |字号大中小 订阅也许细心的你会问：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 p