在u-boot中，通过bootm命令启动内核。bootm命令的作用是将内核加载到指定的内存地址，然后通过R0、R1、R2寄存器传递启动参数之后启动内核。在启动内核之前需要对环境做一些初始化工作，主要有如下几个方面：
(1)、cpu 寄存器设置
* R0 = 0
* R1 = 板级 id
* R2 = 启动参数在内存中的起始地址
(2)、cpu 模式
* 禁止所有中断
* 必须为SVC（超级用户）模式
(3)、缓存、MMU
* 关闭 MMU
* 指令缓存可以开启或者关闭
* 数据缓存必须关闭并且不能包含任何脏数据
(4)、设备
* DMA 设备应当停止工作
(5)、boot loader 需要跳转到内核镜像的第一条指令处
这些需求都由 boot loader 实现，在常用的 uboot 中完成一系列的初始化后最后通过 bootm 命令加载 linux 内核。bootm 将内核镜像从各种媒介中读出，存放在指定的位置；然后设置标记列表给内核传递参数；最后跳到内核的入口点去执行。
在分析u-boot源码之前，我们首先来分析一下u-boot中的命令格式。u-boot中每个命令都是通过 U_BOOT_CMD 宏来定义的，格式如下：
U_BOOT_CMD(name,maxargs,repeatable,command,"usage","help")
各项参数的意义如下：
(1) -- name:命令的名字，注意，它不是一个字符串（不要用双引号括起来）；
(2）-- maxargs:最大的参数个数；
(3）-- repeatable:命令是否可以重复，可重复是指运行一个命令后，下次敲回车即可再次运行；
(4）-- command:对应的函数指针，类型为（*cmd）(struct cmd_tbl_s *, int, int, char *[]);
(5) -- usage:简单的使用说明，这是个字符串；
(6）-- help:较详细的使用说明，这是个字符串。
下面就来具体分析一下bootm命令。bootm命令的源码路径为：u-boot源码路径/common/cmd_bootm.c
我们通过
U_BOOT_CMD( bootm, CONFIG_SYS_MAXARGS, 1, do_bootm, ...)
可以看出bootm命令的入口函数为d_bootm，下面我们就去看一下它的庐山真面目。
/*******************************************************************/ /* bootm - boot application image from image in memory */ /*******************************************************************/ int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[]) { #ifdef CONFIG_ZIMAGE_BOOT #define LINUX_ZIMAGE_MAGIC 0x016f2818 image_header_t *hdr; ulong addr; //找到内核镜像的地址 /* find out kernel image address */ if (argc < 2) { addr = load_addr; debug ("* kernel: default image load address = 0x%08lx\n", load_addr); } else { addr = simple_strtoul(argv[1], NULL, 16); } //检查内核是否为zImage格式 if (*(ulong *)(addr + 9*4) == LINUX_ZIMAGE_MAGIC) { u32 val; printf("Boot with zImage\n"); //将内核地址转换为物理地址 //addr = virt_to_phys(addr); hdr = (image_header_t *)addr; hdr->ih_os = IH_OS_LINUX; hdr->ih_ep = ntohl(addr); //提取内核镜像的头信息 memmove (&images.legacy_hdr_os_copy, hdr, sizeof(image_header_t)); //保存头信息 /* save pointer to image header */ images.legacy_hdr_os = hdr; images.legacy_hdr_valid = 1; goto after_header_check; } #endif #ifdef CONFIG_NEEDS_MANUAL_RELOC static int relocated = 0; //重定位启动函数表 /* relocate boot function table */ if (!relocated) { int i; for (i = 0; i < ARRAY_SIZE(boot_os); i++) if (boot_os[i] != NULL) boot_os[i] += gd->reloc_off; relocated = 1; } #endif //判断是否有子命令 /* determine if we have a sub command */ if (argc > 1) { char *endp; simple_strtoul(argv[1], &endp, 16); /* endp pointing to NULL means that argv[1] was just a * valid number, pass it along to the normal bootm processing * * If endp is ':' or '#' assume a FIT identifier so pass * along for normal processing. * * Right now we assume the first arg should never be '-' */ if ((*endp != 0) && (*endp != ':') && (*endp != '#')) return do_bootm_subcommand(cmdtp, flag, argc, argv); } //获取内核相关信息 if (bootm_start(cmdtp, flag, argc, argv)) return 1; /* * We have reached the point of no return: we are going to * overwrite all exception vector code, so we cannot easily * recover from any failures any more... */ //关闭中断 iflag = disable_interrupts(); #if defined(CONFIG_CMD_USB) /* * turn off USB to prevent the host controller from writing to the * SDRAM while Linux is booting. This could happen (at least for OHCI * controller), because the HCCA (Host Controller Communication Area) * lies within the SDRAM and the host controller writes continously to * this area (as busmaster!). The HccaFrameNumber is for example * updated every 1 ms within the HCCA structure in SDRAM! For more * details see the OpenHCI specification. */ //关闭USB usb_stop(); #endif //加载内核 ret = bootm_load_os(images.os, &load_end, 1); if (ret < 0) { if (ret == BOOTM_ERR_RESET) do_reset (cmdtp, flag, argc, argv); if (ret == BOOTM_ERR_OVERLAP) { if (images.legacy_hdr_valid) { if (image_get_type (&images.legacy_hdr_os_copy) == IH_TYPE_MULTI) puts ("WARNING: legacy format multi component " "image overwritten\n"); } else { puts ("ERROR: new format image overwritten - " "must RESET the board to recover\n"); show_boot_progress (-113); do_reset (cmdtp, flag, argc, argv); } } if (ret == BOOTM_ERR_UNIMPLEMENTED) { if (iflag) enable_interrupts(); show_boot_progress (-7); return 1; } } lmb_reserve(&images.lmb, images.os.load, (load_end - images.os.load)); if (images.os.type == IH_TYPE_STANDALONE) { if (iflag) enable_interrupts(); /* This may return when 'autostart' is 'no' */ bootm_start_standalone(iflag, argc, argv); return 0; } show_boot_progress (8); #if defined(CONFIG_ZIMAGE_BOOT) after_header_check: images.os.os = hdr->ih_os; images.ep = image_get_ep (&images.legacy_hdr_os_copy); #endif #ifdef CONFIG_SILENT_CONSOLE if (images.os.os == IH_OS_LINUX) fixup_silent_linux(); #endif //获取内核启动参数 boot_fn = boot_os[images.os.os]; if (boot_fn == NULL) { if (iflag) enable_interrupts(); printf ("ERROR: booting os '%s' (%d) is not supported\n", genimg_get_os_name(images.os.os), images.os.os); show_boot_progress (-8); return 1; } //内核启动前的准备 arch_preboot_os(); //启动内核，不返回 boot_fn(0, argc, argv, &images); show_boot_progress (-9); #ifdef DEBUG puts ("\n## Control returned to monitor - resetting...\n"); #endif do_reset (cmdtp, flag, argc, argv); return 1; }
该函数主要的工作流程是，通过bootm_start来获取内核镜像文件的信息，然后通过bootm_load_os函数来加载内核，最后通过boot_fn来启动内核。
首先看一下bootm_start，该函数主要进行镜像的有效性判定、校验、计算入口地址等操作，大部分工作通过 boot_get_kernel -> image_get_kernel 完成。
static int bootm_start(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[]) { void *os_hdr; int ret; memset ((void *)&images, 0, sizeof (images)); //读取环境变量，从环境变量中检查是否要对镜像的数据（不是镜像头）进行校验 images.verify = getenv_yesno ("verify"); //不做任何有意义的工作，除了定义# define lmb_reserve(lmb, base, size) bootm_start_lmb(); //获取镜像头，加载地址，长度，返回指向内存中镜像头的指针 /* get kernel image header, start address and length */ os_hdr = boot_get_kernel (cmdtp, flag, argc, argv, &images, &images.os.image_start, &images.os.image_len); if (images.os.image_len == 0) { puts ("ERROR: can't get kernel image!\n"); return 1; } //根据镜像魔数获取镜像类型 /* get image parameters */ switch (genimg_get_format (os_hdr)) { case IMAGE_FORMAT_LEGACY: images.os.type = image_get_type (os_hdr);//镜像类型 images.os.comp = image_get_comp (os_hdr);//压缩类型 images.os.os = image_get_os (os_hdr);//操作系统类型 images.os.end = image_get_image_end (os_hdr);//当前镜像的尾地址 images.os.load = image_get_load (os_hdr);//镜像数据的载入地址 break; #if defined(CONFIG_FIT) case IMAGE_FORMAT_FIT: if (fit_image_get_type (images.fit_hdr_os, images.fit_noffset_os, &images.os.type)) { puts ("Can't get image type!\n"); show_boot_progress (-109); return 1; } if (fit_image_get_comp (images.fit_hdr_os, images.fit_noffset_os, &images.os.comp)) { puts ("Can't get image compression!\n"); show_boot_progress (-110); return 1; } if (fit_image_get_os (images.fit_hdr_os, images.fit_noffset_os, &images.os.os)) { puts ("Can't get image OS!\n"); show_boot_progress (-111); return 1; } images.os.end = fit_get_end (images.fit_hdr_os); if (fit_image_get_load (images.fit_hdr_os, images.fit_noffset_os, &images.os.load)) { puts ("Can't get image load address!\n"); show_boot_progress (-112); return 1; } break; #endif default: puts ("ERROR: unknown image format type!\n"); return 1; } //获取内核入口地址 /* find kernel entry point */ if (images.legacy_hdr_valid) { images.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, &images.ep); if (ret) { puts ("Can't get entry point property!\n"); return 1; } #endif } else { puts ("Could not find kernel entry point!\n"); return 1; } if (((images.os.type == IH_TYPE_KERNEL) || (images.os.type == IH_TYPE_MULTI)) && (images.os.os == IH_OS_LINUX)) { //获取虚拟磁盘 /* find ramdisk */ ret = boot_get_ramdisk (argc, argv, &images, IH_INITRD_ARCH, &images.rd_start, &images.rd_end); if (ret) { puts ("Ramdisk image is corrupt or invalid\n"); return 1; } #if defined(CONFIG_OF_LIBFDT) //获取设备树，设备树是linux 3.XX版本特有的 /* find flattened device tree */ ret = boot_get_fdt (flag, argc, argv, &images, &images.ft_addr, &images.ft_len); if (ret) { puts ("Could not find a valid device tree\n"); return 1; } set_working_fdt_addr(images.ft_addr); #endif } //将内核加载地址赋值给images.os.start images.os.start = (ulong)os_hdr; //更新镜像状态 images.state = BOOTM_STATE_START; return 0; }
接着看一下bootm_load_os函数，它的主要工作是解压内核镜像文件，并且将它移动到内核加载地址。
首先看一下两个重要的结构体
//include/image.h typedef struct image_header { uint32_t ih_magic; /* Image Header Magic Number */ uint32_t ih_hcrc; /* Image Header CRC Checksum */ uint32_t ih_time; /* Image Creation Timestamp */ uint32_t ih_size; /* Image Data Size */ uint32_t ih_load; /* Data Load Address */ uint32_t ih_ep; /* Entry Point Address */ uint32_t ih_dcrc; /* Image Data CRC Checksum */ uint8_t ih_os; /* Operating System */ uint8_t ih_arch; /* CPU architecture */ uint8_t ih_type; /* Image Type */ uint8_t ih_comp; /* Compression Type */ uint8_t ih_name[IH_NMLEN]; /* Image Name */ } image_header_t; typedef struct image_info { ulong start, end; /* start/end of blob */ ulong image_start, image_len; /* start of image within blob, len of image */ ulong load; /* load addr for the image */ uint8_t comp, type, os; /* compression, type of image, os type */ } image_info_t;
static int bootm_start(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[]) { void *os_hdr; int ret; memset ((void *)&images, 0, sizeof (images)); //读取环境变量，从环境变量中检查是否要对镜像的数据（不是镜像头）进行校验 images.verify = getenv_yesno ("verify"); //不做任何有意义的工作，除了定义# define lmb_reserve(lmb, base, size) bootm_start_lmb(); //获取镜像头，加载地址，长度，返回指向内存中镜像头的指针 /* get kernel image header, start address and length */ os_hdr = boot_get_kernel (cmdtp, flag, argc, argv, &images, &images.os.image_start, &images.os.image_len); if (images.os.image_len == 0) { puts ("ERROR: can't get kernel image!\n"); return 1; } //根据镜像魔数获取镜像类型 /* get image parameters */ switch (genimg_get_format (os_hdr)) { case IMAGE_FORMAT_LEGACY: images.os.type = image_get_type (os_hdr);//镜像类型 images.os.comp = image_get_comp (os_hdr);//压缩类型 images.os.os = image_get_os (os_hdr);//操作系统类型 images.os.end = image_get_image_end (os_hdr);//当前镜像的尾地址 images.os.load = image_get_load (os_hdr);//镜像数据的载入地址 break; #if defined(CONFIG_FIT) case IMAGE_FORMAT_FIT: if (fit_image_get_type (images.fit_hdr_os, images.fit_noffset_os, &images.os.type)) { puts ("Can't get image type!\n"); show_boot_progress (-109); return 1; } if (fit_image_get_comp (images.fit_hdr_os, images.fit_noffset_os, &images.os.comp)) { puts ("Can't get image compression!\n"); show_boot_progress (-110); return 1; } if (fit_image_get_os (images.fit_hdr_os, images.fit_noffset_os, &images.os.os)) { puts ("Can't get image OS!\n"); show_boot_progress (-111); return 1; } images.os.end = fit_get_end (images.fit_hdr_os); if (fit_image_get_load (images.fit_hdr_os, images.fit_noffset_os, &images.os.load)) { puts ("Can't get image load address!\n"); show_boot_progress (-112); return 1; } break; #endif default: puts ("ERROR: unknown image format type!\n"); return 1; } //获取内核入口地址 /* find kernel entry point */ if (images.legacy_hdr_valid) { images.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, &images.ep); if (ret) { puts ("Can't get entry point property!\n"); return 1; } #endif } else { puts ("Could not find kernel entry point!\n"); return 1; } if (((images.os.type == IH_TYPE_KERNEL) || (images.os.type == IH_TYPE_MULTI)) && (images.os.os == IH_OS_LINUX)) { //获取虚拟磁盘 /* find ramdisk */ ret = boot_get_ramdisk (argc, argv, &images, IH_INITRD_ARCH, &images.rd_start, &images.rd_end); if (ret) { puts ("Ramdisk image is corrupt or invalid\n"); return 1; } #if defined(CONFIG_OF_LIBFDT) //获取设备树，设备树是linux 3.XX版本特有的 /* find flattened device tree */ ret = boot_get_fdt (flag, argc, argv, &images, &images.ft_addr, &images.ft_len); if (ret) { puts ("Could not find a valid device tree\n"); return 1; } set_working_fdt_addr(images.ft_addr); #endif } //将内核加载地址赋值给images.os.start images.os.start = (ulong)os_hdr; //更新镜像状态 images.state = BOOTM_STATE_START; return 0; } #define BOOTM_ERR_RESET -1 #define BOOTM_ERR_OVERLAP -2 #define BOOTM_ERR_UNIMPLEMENTED -3 static int bootm_load_os(image_info_t os, ulong *load_end, int boot_progress) { uint8_t comp = os.comp;//压缩格式 ulong load = os.load;//加载地址 ulong blob_start = os.start;//系统起始地址 ulong blob_end = os.end;//系统结束地址 ulong image_start = os.image_start;//镜像起始地址 ulong image_len = os.image_len;//镜像大小 uint unc_len = CONFIG_SYS_BOOTM_LEN;//镜像最大长度 #if defined(CONFIG_LZMA) || defined(CONFIG_LZO) int ret; #endif /* defined(CONFIG_LZMA) || defined(CONFIG_LZO) */ //获取镜像类型 const char *type_name = genimg_get_type_name (os.type); switch (comp) { case IH_COMP_NONE://镜像没有压缩过 if (load == blob_start) {//判断是否需要移动镜像 printf (" XIP %s ... ", type_name); } else { printf (" Loading %s ... ", type_name); memmove_wd ((void *)load, (void *)image_start, image_len, CHUNKSZ); } *load_end = load + image_len; puts("OK\n"); break; #ifdef CONFIG_GZIP case IH_COMP_GZIP://镜像使用gzip压缩 printf (" Uncompressing %s ... ", type_name); //解压镜像文件 if (gunzip ((void *)load, unc_len, (uchar *)image_start, &image_len) != 0) { puts ("GUNZIP: uncompress, out-of-mem or overwrite error " "- must RESET board to recover\n"); if (boot_progress) show_boot_progress (-6); return BOOTM_ERR_RESET; } *load_end = load + image_len; break; #endif /* CONFIG_GZIP */ ...... return 0; }
最后看一下boot_fn函数，boot_fn的定义为
boot_os_fn *boot_fn;
可以看出它是一个boot_os_fn类型的函数指针。它的定义为
// common/cmd_bootm.c typedef int boot_os_fn (int flag, int argc, char * const argv[], bootm_headers_t *images); /* pointers to os/initrd/fdt */ #ifdef CONFIG_BOOTM_LINUX extern boot_os_fn do_bootm_linux; #endif ......
然后boot_fn在do_bootm函数中被赋值为
boot_fn = boot_os[images.os.os];
boot_os是一个函数指针数组
// common/cmd_bootm.c static boot_os_fn *boot_os[] = { #ifdef CONFIG_BOOTM_LINUX [IH_OS_LINUX] = do_bootm_linux, #endif #ifdef CONFIG_BOOTM_NETBSD [IH_OS_NETBSD] = do_bootm_netbsd, #endif #ifdef CONFIG_LYNXKDI [IH_OS_LYNXOS] = do_bootm_lynxkdi, #endif #ifdef CONFIG_BOOTM_RTEMS [IH_OS_RTEMS] = do_bootm_rtems, #endif #if defined(CONFIG_BOOTM_OSE) [IH_OS_OSE] = do_bootm_ose, #endif #if defined(CONFIG_CMD_ELF) [IH_OS_VXWORKS] = do_bootm_vxworks, [IH_OS_QNX] = do_bootm_qnxelf, #endif #ifdef CONFIG_INTEGRITY [IH_OS_INTEGRITY] = do_bootm_integrity, #endif };
可以看出 boot_fn 函数指针最后指向的函数是位于 arch/arm/lib/bootm.c的 do_bootm_linux，这是内核启动前最后的一个函数，该函数主要完成启动参数的初始化，并将板子设定为满足内核启动的环境。
int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images) { //从全局变量结构体中获取串口参数 bd_t *bd = gd->bd; char *s; //获取机器码 int machid = bd->bi_arch_number; //内核入口函数 void (*kernel_entry)(int zero, int arch, uint params); int ret; //获取启动参数 #ifdef CONFIG_CMDLINE_TAG char *commandline = getenv ("bootargs"); #endif if ((flag != 0) && (flag != BOOTM_STATE_OS_GO)) return 1; //从环境变量中获取机器码 s = getenv ("machid"); if (s) { machid = simple_strtoul (s, NULL, 16); printf ("Using machid 0x%x from environment\n", machid); } //获取ramdisk ret = boot_get_ramdisk(argc, argv, images, IH_ARCH_ARM, &(images->rd_start), &(images->rd_end)); if(ret) printf("[err] boot_get_ramdisk\n"); show_boot_progress (15); #ifdef CONFIG_OF_LIBFDT if (images->ft_len) return bootm_linux_fdt(machid, images); #endif kernel_entry = (void (*)(int, int, uint))images->ep; debug ("## Transferring control to Linux (at address %08lx) ...\n", (ulong) kernel_entry); #if defined (CONFIG_SETUP_MEMORY_TAGS) || \ defined (CONFIG_CMDLINE_TAG) || \ defined (CONFIG_INITRD_TAG) || \ defined (CONFIG_SERIAL_TAG) || \ defined (CONFIG_REVISION_TAG) setup_start_tag (bd); #ifdef CONFIG_SERIAL_TAG setup_serial_tag (params); #endif #ifdef CONFIG_REVISION_TAG setup_revision_tag (params); #endif #ifdef CONFIG_SETUP_MEMORY_TAGS setup_memory_tags (bd); #endif #ifdef CONFIG_CMDLINE_TAG setup_commandline_tag (bd, commandline); #endif #ifdef CONFIG_INITRD_TAG if (images->rd_start && images->rd_end) setup_initrd_tag (bd, images->rd_start, images->rd_end); #endif setup_end_tag(bd); #endif announce_and_cleanup(); #ifdef CONFIG_ENABLE_MMU theLastJump((void *)virt_to_phys(kernel_entry), machid, bd->bi_boot_params); #else kernel_entry(0, machid, bd->bi_boot_params); /* does not return */ #endif return 1; }
kernel_entry(0, machid, r2)
真正将控制权交给内核， 启动内核；
满足arm架构linux内核启动时的寄存器设置条件:第一个参数为0 ；第二个参数为板子id需与内核中的id匹配，第三个参数为启动参数地址bi_boot_params 。
（1）首先取出环境变量bootargs，这就是要传递给内核的参数。
（2）调用setup_XXX_tag
static void setup_start_tag (bd_t *bd) { //将tags的首地址也就是bi_boot_params传给kernel params = (struct tag *) bd->bi_boot_params; params->hdr.tag = ATAG_CORE; params->hdr.size = tag_size (tag_core); params->u.core.flags = 0; params->u.core.pagesize = 0; params->u.core.rootdev = 0; params = tag_next (params); }
params是一个用来存储要传给kernel的参数的静态全局变量。
u-boot 是通过标记列表向内核传递参数，标记在源代码中定义为tag,是一个结构体，在 arch/arm/include/asm/setup.h 中定义。
struct tag { struct tag_header hdr; union { struct tag_core core; struct tag_mem32 mem; struct tag_videotext videotext; struct tag_ramdisk ramdisk; struct tag_initrd initrd; struct tag_serialnr serialnr; struct tag_revision revision; struct tag_videolfb videolfb; struct tag_cmdline cmdline; /* * Acorn specific */ struct tag_acorn acorn; /* * DC21285 specific */ struct tag_memclk memclk; } u;
tag包括hdr和各种类型的tag_*,hdr来标志当前的tag是哪种类型的tag。setup_start_tag是初始化了第一个tag，是tag_core类型的tag。最后调用tag_next跳到第一个tag末尾，为下一个tag做准备。
tag_next是一个宏定义，被定义在arch/arm/include/asm/setup.h中
#define tag_next(t) ((struct tag *)((u32 *)(t) + (t)->hdr.size))
struct tag_header { u32 size; u32 tag; };
最后调用setup_end_tag，将末尾的tag设置为ATAG_NONE，标志tag列表结束。
static void setup_end_tag (bd_t *bd) { params->hdr.tag = ATAG_NONE; params->hdr.size = 0; }
u-boot将参数以tag数组的形式布局在内存的某一个地址，每个tag代表一种类型的参数，首尾tag标志开始和结束，首地址传给kernel供其解析
通过上面的分析，我们可以尝试自己写一个bootm来引导内核（代码与4412无关，是学6410时的笔记）
//atag.h #define ATAG_CORE 0x54410001 #define ATAG_MEM 0x54410002 #define ATAG_CMDLINE 0x54410009 #define ATAG_NONE 0x00000000 struct tag_header { unsigned int size; unsigned int tag; }; struct tag_core { unsigned int flags; unsigned int pagesize; unsigned int rootdev; }; struct tag_mem32 { unsigned int size; unsigned int start; }; struct tag_cmdline { char cmdline[1]; }; struct tag { struct tag_header hdr; union { struct tag_core core; struct tag_mem32 mem; struct tag_cmdline cmdline; } u; }; #define tag_size(type) ((sizeof(struct tag_header) + sizeof(struct type)) >> 2) #define tag_next(t) ((struct tag *)((unsigned int *)(t) + (t)->hdr.size))
//boot.c #include "atag.h" #include "string.h" void (*theKernel)(int , int , unsigned int ); #define SDRAM_KERNEL_START 0x51000000 #define SDRAM_TAGS_START 0x50000100 #define SDRAM_ADDR_START 0x50000000 #define SDRAM_TOTAL_SIZE 0x16000000 struct tag *pCurTag; const char *cmdline = "console=ttySAC0,115200 init=/init"; void setup_core_tag() { pCurTag = (struct tag *)SDRAM_TAGS_START; pCurTag->hdr.tag = ATAG_CORE; pCurTag->hdr.size = tag_size(tag_core); pCurTag->u.core.flags = 0; pCurTag->u.core.pagesize = 4096; pCurTag->u.core.rootdev = 0; pCurTag = tag_next(pCurTag); } void setup_mem_tag() { pCurTag->hdr.tag = ATAG_MEM; pCurTag->hdr.size = tag_size(tag_mem32); pCurTag->u.mem.start = SDRAM_ADDR_START; pCurTag->u.mem.size = SDRAM_TOTAL_SIZE; pCurTag = tag_next(pCurTag); } void setup_cmdline_tag() { int linelen = strlen(cmdline); pCurTag->hdr.tag = ATAG_CMDLINE; pCurTag->hdr.size = (sizeof(struct tag_header)+linelen+1+4)>>2; strcpy(pCurTag->u.cmdline.cmdline,cmdline); pCurTag = tag_next(pCurTag); } void setup_end_tag() { pCurTag->hdr.tag = ATAG_NONE; pCurTag->hdr.size = 0; } void boot_linux(){ //1.获取Linux启动地址 theKernel = (void (*)(int , int , unsigned int ))SDRAM_KERNEL_START; printf("huo qu linux qi dong di zhi"); //2.设置启动参数 //2.1.设置核心启动参数 setup_core_tag(); //2.2.设置内存参数 setup_mem_tag(); //2.3.设置命令行参数 setup_cmdline_tag(); //2.4.设置结束标志 setup_end_tag(); //4.启动Linux内核 theKernel(0,1626,SDRAM_TAGS_START); printf("qi dong linux nei he"); }