U-Boot与Linux内核的交互

olga

U-Boot与Linux内核的交互

　　说明：本文所使用的U-Boot的版本是1.1.6，平台是S3C2440。
目录
一、简介
1.1标记列表
二、设置标记存放的地址
2.1相关的结构体定义
2.2标记存放地址的设定
三、标记的设置
3.1设置标记ATAG_CORE
3.2设置内存标记ATAG_MEM
3.3设置命令行标记ATAG_CMDLINE
3.4设置ATAG_NONE
一、简介　　U-Boot与Linux内核的交互是单向的，U-Boot将各类参数传递给讷河。由于他们不能同时运行，传递办法只能有一个个：U-Boot将参数放在某个约定的地方之后，在启动内核，内核启动后从这个地方获得参数。
1.1标记列表　　除了约定好参数存放的地方外，还要规定参数的结构。Linux2.4.x以后的内核都以标记列表（tagged list）的形式来传递参数。标记就是一种数据结构；标记列表就是挨着存放的多个标记。标记列表以标记ATAG_CORE开始，以ATAGE_NONE结束。
　　标记的数据结构为tag，它是偶一个tag_header结构和一个联合体（union）组成。tag_header结构体表示标记的类型及长度，比如是表示内存还是表示命令行参数等。对于不同类型的标记使用不同的联合体，比如表示内存=时使用tag_men32，表示命令行时使用tag_cmdline。其定定义在include/asm-arm/setup.c文件中。
　　



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• /*
  
• * The new way of passing information: a list of tagged entries
  
• */
  
• 
  
• /* The list ends with an ATAG_NONE node. */
  
• #define ATAG_NONE   0x00000000
  
• 
  
• struct tag_header {
  
•     u32 size;
  
•     u32 tag;
  
• };
  
• 
  
• /* The list must start with an ATAG_CORE node */
  
• #define ATAG_CORE   0x54410001
  
• 
  
• struct tag_core {
  
•     u32 flags;      /* bit 0 = read-only */
  
•     u32 pagesize;
  
•     u32 rootdev;
  
• };
  
• 
  
• /* it is allowed to have multiple ATAG_MEM nodes */
  
• #define ATAG_MEM    0x54410002
  
• 
  
• struct tag_mem32 {
  
•     u32 size;
  
•     u32 start;  /* physical start address */
  
• };
  
• 
  
• /* VGA text type displays */
  
• #define ATAG_VIDEOTEXT  0x54410003
  
• 
  
• struct tag_videotext {
  
•     u8      x;
  
•     u8      y;
  
•     u16     video_page;
  
•     u8      video_mode;
  
•     u8      video_cols;
  
•     u16     video_ega_bx;
  
•     u8      video_lines;
  
•     u8      video_isvga;
  
•     u16     video_points;
  
• };
  
• 
  
• /* describes how the ramdisk will be used in kernel */
  
• #define ATAG_RAMDISK    0x54410004
  
• 
  
• struct tag_ramdisk {
  
•     u32 flags;  /* bit 0 = load, bit 1 = prompt */
  
•     u32 size;   /* decompressed ramdisk size in _kilo_ bytes */
  
•     u32 start;  /* starting block of floppy-based RAM disk image */
  
• };
  
• 
  
• /* describes where the compressed ramdisk image lives (virtual address) */
  
• /*
  
• * this one accidentally used virtual addresses - as such,
  
• * its depreciated.
  
• */
  
• #define ATAG_INITRD 0x54410005
  
• 
  
• /* describes where the compressed ramdisk image lives (physical address) */
  
• #define ATAG_INITRD2    0x54420005
  
• 
  
• struct tag_initrd {
  
•     u32 start;  /* physical start address */
  
•     u32 size;   /* size of compressed ramdisk image in bytes */
  
• };
  
• 
  
• /* board serial number. "64 bits should be enough for everybody" */
  
• #define ATAG_SERIAL 0x54410006
  
• 
  
• struct tag_serialnr {
  
•     u32 low;
  
•     u32 high;
  
• };
  
• 
  
• /* board revision */
  
• #define ATAG_REVISION   0x54410007
  
• 
  
• struct tag_revision {
  
•     u32 rev;
  
• };
  
• 
  
• /* initial values for vesafb-type framebuffers. see struct screen_info
  
• * in include/linux/tty.h
  
• */
  
• #define ATAG_VIDEOLFB   0x54410008
  
• 
  
• struct tag_videolfb {
  
•     u16     lfb_width;
  
•     u16     lfb_height;
  
•     u16     lfb_depth;
  
•     u16     lfb_linelength;
  
•     u32     lfb_base;
  
•     u32     lfb_size;
  
•     u8      red_size;
  
•     u8      red_pos;
  
•     u8      green_size;
  
•     u8      green_pos;
  
•     u8      blue_size;
  
•     u8      blue_pos;
  
•     u8      rsvd_size;
  
•     u8      rsvd_pos;
  
• };
  
• 
  
• /* command line: \0 terminated string */
  
• #define ATAG_CMDLINE    0x54410009
  
• 
  
• struct tag_cmdline {
  
•     char    cmdline[1]; /* this is the minimum size */
  
• };
  
• 
  
• /* acorn RiscPC specific information */
  
• #define ATAG_ACORN  0x41000101
  
• 
  
• struct tag_acorn {
  
•     u32 memc_control_reg;
  
•     u32 vram_pages;
  
•     u8 sounddefault;
  
•     u8 adfsdrives;
  
• };
  
• 
  
• /* footbridge memory clock, see arch/arm/mach-footbridge/arch.c */
  
• #define ATAG_MEMCLK 0x41000402
  
• 
  
• struct tag_memclk {
  
•     u32 fmemclk;
  
• };
  
• 
  
• 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;
  
• };
  
• 
  
• #define tag_next(t)  ((struct tag *)((u32 *)(t) + (t)->hdr.size))
  
• #define tag_size(type)   ((sizeof(struct tag_header) + sizeof(struct type)) >> 2) //???
  

/** The new way of passing information: a list of tagged entries*//* The list ends with an ATAG_NONE node. */#define ATAG_NONE0x00000000struct tag_header {u32 size;u32 tag;};/* The list must start with an ATAG_CORE node */#define ATAG_CORE0x54410001struct tag_core {u32 flags;/* bit 0 = read-only */u32 pagesize;u32 rootdev;};/* it is allowed to have multiple ATAG_MEM nodes */#define ATAG_MEM0x54410002struct tag_mem32 {u32size;u32start;/* physical start address */};/* VGA text type displays */#define ATAG_VIDEOTEXT0x54410003struct tag_videotext {u8x;u8y;u16video_page;u8video_mode;u8video_cols;u16video_ega_bx;u8video_lines;u8video_isvga;u16video_points;};/* describes how the ramdisk will be used in kernel */#define ATAG_RAMDISK0x54410004struct tag_ramdisk {u32 flags;/* bit 0 = load, bit 1 = prompt */u32 size;/* decompressed ramdisk size in _kilo_ bytes */u32 start;/* starting block of floppy-based RAM disk image */};/* describes where the compressed ramdisk image lives (virtual address) *//** this one accidentally used virtual addresses - as such,* its depreciated.*/#define ATAG_INITRD0x54410005/* describes where the compressed ramdisk image lives (physical address) */#define ATAG_INITRD20x54420005struct tag_initrd {u32 start;/* physical start address */u32 size;/* size of compressed ramdisk image in bytes */};/* board serial number. "64 bits should be enough for everybody" */#define ATAG_SERIAL0x54410006struct tag_serialnr {u32 low;u32 high;};/* board revision */#define ATAG_REVISION0x54410007struct tag_revision {u32 rev;};/* initial values for vesafb-type framebuffers. see struct screen_info* in include/linux/tty.h*/#define ATAG_VIDEOLFB0x54410008struct tag_videolfb {u16lfb_width;u16lfb_height;u16lfb_depth;u16lfb_linelength;u32lfb_base;u32lfb_size;u8red_size;u8red_pos;u8green_size;u8green_pos;u8blue_size;u8blue_pos;u8rsvd_size;u8rsvd_pos;};/* command line: \0 terminated string */#define ATAG_CMDLINE0x54410009struct tag_cmdline {charcmdline[1];/* this is the minimum size */};/* acorn RiscPC specific information */#define ATAG_ACORN0x41000101struct tag_acorn {u32 memc_control_reg;u32 vram_pages;u8 sounddefault;u8 adfsdrives;};/* footbridge memory clock, see arch/arm/mach-footbridge/arch.c */#define ATAG_MEMCLK0x41000402struct tag_memclk {u32 fmemclk;};struct tag {struct tag_header hdr;union {struct tag_corecore;struct tag_mem32mem;struct tag_videotextvideotext;struct tag_ramdiskramdisk;struct tag_initrdinitrd;struct tag_serialnrserialnr;struct tag_revisionrevision;struct tag_videolfbvideolfb;struct tag_cmdlinecmdline;/** Acorn specific*/struct tag_acornacorn;/** DC21285 specific*/struct tag_memclkmemclk;} u;};#define tag_next(t)((struct tag *)((u32 *)(t) + (t)->hdr.size))#define tag_size(type)((sizeof(struct tag_header) + sizeof(struct type)) >> 2) //???二、设置标记存放的地址2.1相关的结构体定义　　
　　结构体bd中保存了标记存放的地址。bd结构体是gd结构体的一项，我们先看gd结构体，其定义在include/asm-arm/global_data.h文件中：
　　



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• typedef struct  global_data {
  
•     bd_t        *bd;//开发板相关参数 ,结构体变量，参考u-boot.h
  
•     unsigned long   flags;//指示标志，如设备已经初始化标志等
  
•     unsigned long   baudrate;//串行口通讯速率
  
•     unsigned long   have_console;
  
•     /* serial_init() was called 如果执行了该函数，则设置为1 */
  
•     unsigned long   reloc_off;
  
•     /*
  
•      *Relocation Offset 重定位偏移，就是实际定向的位置与编译连接时指定的位置之差，一般为0
  
•         */
  
•     unsigned long   env_addr;   /* 环境参数地址*/
  
•     unsigned long   env_valid;  /* 环境参数CRC检验有效标志*/
  
•     unsigned long   fb_base;    /*帧缓冲区基地址*/
  
• #ifdef CONFIG_VFD
  
•     unsigned char   vfd_type;   /* 显示类型*/
  
• #endif
  
• #if 0
  
•     unsigned long   cpu_clk;    /*cpu时钟*/
  
•     unsigned long   bus_clk;    //总线时钟
  
•     unsigned long   ram_size;   /* RAM size */
  
•     unsigned long   reset_status;   /* reset status register at boot */
  
• #endif
  
•     void        **jt;   /* jump table 跳转表，用来登记"函数调用地址"*/
  
• } gd_t;
  

typedefstructglobal_data {bd_t*bd;//开发板相关参数 ,结构体变量，参考u-boot.h unsigned longflags;//指示标志，如设备已经初始化标志等unsigned longbaudrate;//串行口通讯速率unsigned longhave_console;/* serial_init() was called 如果执行了该函数，则设置为1 */unsigned longreloc_off;/* *Relocation Offset 重定位偏移，就是实际定向的位置与编译连接时指定的位置之差，一般为0*/unsigned longenv_addr;/* 环境参数地址*/unsigned longenv_valid;/* 环境参数CRC检验有效标志*/unsigned longfb_base;/*帧缓冲区基地址*/#ifdef CONFIG_VFDunsigned charvfd_type;/* 显示类型*/#endif#if 0unsigned longcpu_clk;/*cpu时钟*/unsigned longbus_clk;    //总线时钟unsigned longram_size;/* RAM size */unsigned longreset_status;/* reset status register at boot */#endifvoid**jt;/* jump table 跳转表，用来登记"函数调用地址"*/} gd_t;接来下我们来看一下bd结构体，这个结构体定义在include/asm-arm/u-boot.h文件中：　　
　　



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• typedef struct bd_info {
  
•     int         bi_baudrate;    /* 串口波特率*/
  
•     unsigned long   bi_ip_addr; /*  IP 地址*/
  
•     unsigned char   bi_enetaddr[6]; /* MAC地址*/
  
•     struct environment_s           *bi_env;
  
•     ulong           bi_arch_number; /*  板子的id*/
  
•     ulong           bi_boot_params; /* 启动参数*/
  
•     struct              /* RAM 配置*/
  
•     {
  
•     ulong start;
  
•     ulong size;
  
•     }bi_dram[CONFIG_NR_DRAM_BANKS];
  
• #ifdef CONFIG_HAS_ETH1
  
•     /* second onboard ethernet port */
  
•     unsigned char   bi_enet1addr[6];
  
• #endif
  
• } bd_t;
  

typedef struct bd_info {intbi_baudrate;/* 串口波特率*/unsigned longbi_ip_addr;/*  IP 地址*/unsigned charbi_enetaddr[6]; /* MAC地址*/struct environment_s       *bi_env;ulong        bi_arch_number;/*  板子的id*/ulong        bi_boot_params;/* 启动参数*/struct/* RAM 配置*/{ulong start;ulong size;}bi_dram[CONFIG_NR_DRAM_BANKS];#ifdef CONFIG_HAS_ETH1/* second onboard ethernet port */unsigned char   bi_enet1addr[6];#endif} bd_t;2.2标记存放地址的设定　　
　　在board/smdk2410/smdk2410.c的board_init 函数设置了bi_boot_params 参数：
　　



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• int board_init (void)
  
• {
  
•     S3C24X0_CLOCK_POWER * const clk_power = S3C24X0_GetBase_CLOCK_POWER();//获取时钟和电源配置寄存器的第一个寄存器的地址，寄存器的地上是连续的
  
•     S3C24X0_GPIO * const gpio = S3C24X0_GetBase_GPIO();//获取GPIO配置寄存器的第一个寄存器的地址
  
• 
  
•     /* to reduce PLL lock time, adjust the LOCKTIME register */
  
•     clk_power->LOCKTIME = 0xFFFFFF;
  
• 
  
•     /* configure MPLL */
  
•     clk_power->MPLLCON = ((M_MDIV GPBUP = 0x000007FF;
  
•     gpio->GPCCON = 0xAAAAAAAA;
  
•     gpio->GPCUP = 0x0000FFFF;
  
•     gpio->GPDCON = 0xAAAAAAAA;
  
•     gpio->GPDUP = 0x0000FFFF;
  
•     gpio->GPECON = 0xAAAAAAAA;
  
•     gpio->GPEUP = 0x0000FFFF;
  
•     gpio->GPFCON = 0x000055AA;
  
•     gpio->GPFUP = 0x000000FF;
  
•     gpio->GPGCON = 0xFF95FFBA;
  
•     gpio->GPGUP = 0x0000FFFF;
  
•     gpio->GPHCON = 0x002AFAAA;
  
•     gpio->GPHUP = 0x000007FF;
  
• 
  
•     /* arch number of SMDK2410-Board */
  
•     gd->bd->bi_arch_number = MACH_TYPE_SMDK2410;
  
• 
  
•     /* adress of boot parameters */
  
•     gd->bd->bi_boot_params = 0x30000100;
  
• 
  
•     icache_enable();  //调用cpu/arm920t/cpu.c中的函数
  
•     dcache_enable();
  
• 
  
•     return 0;
  
• }
  

int board_init (void){S3C24X0_CLOCK_POWER * const clk_power = S3C24X0_GetBase_CLOCK_POWER();//获取时钟和电源配置寄存器的第一个寄存器的地址，寄存器的地上是连续的S3C24X0_GPIO * const gpio = S3C24X0_GetBase_GPIO();//获取GPIO配置寄存器的第一个寄存器的地址/* to reduce PLL lock time, adjust the LOCKTIME register */clk_power->LOCKTIME = 0xFFFFFF;/* configure MPLL */clk_power->MPLLCON = ((M_MDIV GPBUP = 0x000007FF;gpio->GPCCON = 0xAAAAAAAA;gpio->GPCUP = 0x0000FFFF;gpio->GPDCON = 0xAAAAAAAA;gpio->GPDUP = 0x0000FFFF;gpio->GPECON = 0xAAAAAAAA;gpio->GPEUP = 0x0000FFFF;gpio->GPFCON = 0x000055AA;gpio->GPFUP = 0x000000FF;gpio->GPGCON = 0xFF95FFBA;gpio->GPGUP = 0x0000FFFF;gpio->GPHCON = 0x002AFAAA;gpio->GPHUP = 0x000007FF;/* arch number of SMDK2410-Board */gd->bd->bi_arch_number = MACH_TYPE_SMDK2410;/* adress of boot parameters */gd->bd->bi_boot_params = 0x30000100;icache_enable();  //调用cpu/arm920t/cpu.c中的函数dcache_enable();return 0;}三、标记的设置　　
　　U-Boot通过bootm命令引导Linux内核，bootm命令对吼调用do_bootm_linux函数来引导内核。在do_bootm_linux函数就设置了标记，该函数的定义在lib_arm/armlinux.c中：
　　



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• void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],
  
•              ulong addr, ulong *len_ptr, int verify)
  
• {
  
•     ulong len = 0, checksum;
  
•     ulong initrd_start, initrd_end;
  
•     ulong data;
  
•     void (*theKernel)(int zero, int arch, uint params);
  
•     image_header_t *hdr = &header;
  
•     bd_t *bd = gd->bd;
  
• 
  
• #ifdef CONFIG_CMDLINE_TAG
  
•     char *commandline = getenv ("bootargs");
  
• #endif
  
• 
  
•     theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
  
•     设置kernal加载地址
  
• 
  
•     /*
  
•      * Check if there is an initrd image
  
•      */
  
•     用户自定义了initrd之后需要加载进来，整个过程需要进行头部以及整个数据内部校，类似于内核的加载校验，这里省略了。
  
• initial RAM disk　　Linux初始 RAM磁盘（initrd）是在系统引导过程中挂载的一个临时根文件系统，用来支持两阶段的引导过程。initrd文件中包含了各种可执行程序和驱动程序，它们可以用来挂载实际的根文件系统，然后再将这个 initrd RAM 磁盘卸载，并释放内存。在很多嵌入式Linux 系统中，initrd 就是最终的根文件系统。
  
•     if (argc >= 3) {
  
•         SHOW_BOOT_PROGRESS (9);
  
• 
  
•         addr = simple_strtoul (argv[2], NULL, 16);
  
• 
  
•         printf ("## Loading Ramdisk Image at %08lx ...\n", addr);
  
• 
  
•         /* Copy header so we can blank CRC field for re-calculation */
  
• #ifdef CONFIG_HAS_DATAFLASH
  
•         if (addr_dataflash (addr)) {
  
•             read_dataflash (addr, sizeof (image_header_t),
  
•                     (char *) &header);
  
•         } else
  
• #endif
  
•             memcpy (&header, (char *) addr,
  
•                 sizeof (image_header_t));
  
• 
  
•         if (ntohl (hdr->ih_magic) != IH_MAGIC) {
  
•             printf ("Bad Magic Number\n");
  
•             SHOW_BOOT_PROGRESS (-10);
  
•             do_reset (cmdtp, flag, argc, argv);
  
•         }
  
• 
  
•         data = (ulong) & header;
  
•         len = sizeof (image_header_t);
  
• 
  
•         checksum = ntohl (hdr->ih_hcrc);
  
•         hdr->ih_hcrc = 0;
  
• 
  
•         if (crc32 (0, (unsigned char *) data, len) != checksum) {
  
•             printf ("Bad Header Checksum\n");
  
•             SHOW_BOOT_PROGRESS (-11);
  
•             do_reset (cmdtp, flag, argc, argv);
  
•         }
  
• 
  
•         SHOW_BOOT_PROGRESS (10);
  
• 
  
•         print_image_hdr (hdr);
  
• 
  
•         data = addr + sizeof (image_header_t);
  
•         len = ntohl (hdr->ih_size);
  
• 
  
• #ifdef CONFIG_HAS_DATAFLASH
  
•         if (addr_dataflash (addr)) {
  
•             read_dataflash (data, len, (char *) CFG_LOAD_ADDR);
  
•             data = CFG_LOAD_ADDR;
  
•         }
  
• #endif
  
• 
  
•         if (verify) {
  
•             ulong csum = 0;
  
• 
  
•             printf ("   Verifying Checksum ... ");
  
•             csum = crc32 (0, (unsigned char *) data, len);
  
•             if (csum != ntohl (hdr->ih_dcrc)) {
  
•                 printf ("Bad Data CRC\n");
  
•                 SHOW_BOOT_PROGRESS (-12);
  
•                 do_reset (cmdtp, flag, argc, argv);
  
•             }
  
•             printf ("OK\n");
  
•         }
  
• 
  
•         SHOW_BOOT_PROGRESS (11);
  
• 
  
•         if ((hdr->ih_os != IH_OS_LINUX) ||
  
•             (hdr->ih_arch != IH_CPU_ARM) ||
  
•             (hdr->ih_type != IH_TYPE_RAMDISK)) {
  
•             printf ("No Linux ARM Ramdisk Image\n");
  
•             SHOW_BOOT_PROGRESS (-13);
  
•             do_reset (cmdtp, flag, argc, argv);
  
•         }
  
• 
  
• #if defined(CONFIG_B2) || defined(CONFIG_EVB4510) || defined(CONFIG_ARMADILLO)
  
•         /*
  
•          *we need to copy the ramdisk to SRAM to let Linux boot
  
•          */
  
•         memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
  
•         data = ntohl(hdr->ih_load);
  
• #endif /* CONFIG_B2 || CONFIG_EVB4510 */
  
• 
  
•         /*
  
•          * Now check if we have a multifile image
  
•          */
  
•     } else if ((hdr->ih_type == IH_TYPE_MULTI) && (len_ptr[1])) {
  
•         ulong tail = ntohl (len_ptr[0]) % 4;
  
•         int i;
  
• 
  
•         SHOW_BOOT_PROGRESS (13);
  
• 
  
•         /* skip kernel length and terminator */
  
•         data = (ulong) (&len_ptr[2]);
  
•         /* skip any additional image length fields */
  
•         for (i = 1; len_ptr; ++i)
  
•             data += 4;
  
•         /* add kernel length, and align */
  
•         data += ntohl (len_ptr[0]);
  
•         if (tail) {
  
•             data += 4 - tail;
  
•         }
  
• 
  
•         len = ntohl (len_ptr[1]);
  
• 
  
•     } else {
  
•         /*
  
•          * no initrd image
  
•          */
  
•         SHOW_BOOT_PROGRESS (14);
  
• 
  
•         len = data = 0;
  
•     }
  
• 
  
• #ifdef  DEBUG
  
•     if (!data) {
  
•         printf ("No initrd\n");
  
•     }
  
• #endif
  
• 
  
•     if (data) {
  
•         initrd_start = data;
  
•         initrd_end = initrd_start + len;
  
•     } else {
  
•         initrd_start = 0;
  
•         initrd_end = 0;
  
•     }
  
• 
  
•     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_VFD)
  
•     setup_start_tag (bd);设置各种tag，用于传递参数给Linux
  
• #ifdef CONFIG_SERIAL_TAG
  
•     setup_serial_tag (¶ms);
  
• #endif
  
• #ifdef CONFIG_REVISION_TAG
  
•     setup_revision_tag (¶ms);
  
• #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 (initrd_start && initrd_end)
  
•         setup_initrd_tag (bd, initrd_start, initrd_end);
  
• #endif
  
• #if defined (CONFIG_VFD) || defined (CONFIG_LCD)
  
•     setup_videolfb_tag ((gd_t *) gd);
  
• #endif
  
•     setup_end_tag (bd);
  
• #endif
  
• 
  
•     /* we assume that the kernel is in place */
  
•     printf ("\nStarting kernel ...\n\n");打印信息
  
• 
  
• #ifdef CONFIG_USB_DEVICE
  
•     {
  
•         extern void udc_disconnect (void);
  
•         udc_disconnect ();
  
•     }
  
• #endif
  
• 
  
•     cleanup_before_linux ();启动之前先做一些清理工作cpu/arm920t/cpu.c
  
• 
  
• 调用内核需要传递的参数如下：
  
• R0：必须为0
  
• R1：机器类型ID，本机为ARM（bd->bi_arch_number）
  
• R2：启动参数列表在内存中的位置（bd->bi_boot_params）
  
•     theKernel (0, bd->bi_arch_number, bd->bi_boot_params);
  
• }
  

void do_bootm_linux (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[],ulong addr, ulong *len_ptr, int verify){ulong len = 0, checksum;ulong initrd_start, initrd_end;ulong data;void (*theKernel)(int zero, int arch, uint params);image_header_t *hdr = &header;bd_t *bd = gd->bd;#ifdef CONFIG_CMDLINE_TAGchar *commandline = getenv ("bootargs");#endiftheKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);设置kernal加载地址/** Check if there is an initrd image*/用户自定义了initrd之后需要加载进来，整个过程需要进行头部以及整个数据内部校，类似于内核的加载校验，这里省略了。initial RAM disk　　Linux初始 RAM磁盘（initrd）是在系统引导过程中挂载的一个临时根文件系统，用来支持两阶段的引导过程。initrd文件中包含了各种可执行程序和驱动程序，它们可以用来挂载实际的根文件系统，然后再将这个 initrd RAM 磁盘卸载，并释放内存。在很多嵌入式Linux 系统中，initrd 就是最终的根文件系统。if (argc >= 3) {SHOW_BOOT_PROGRESS (9);addr = simple_strtoul (argv[2], NULL, 16);printf ("## Loading Ramdisk Image at %08lx ...\n", addr);/* Copy header so we can blank CRC field for re-calculation */#ifdef CONFIG_HAS_DATAFLASHif (addr_dataflash (addr)) {read_dataflash (addr, sizeof (image_header_t),(char *) &header);} else#endifmemcpy (&header, (char *) addr,sizeof (image_header_t));if (ntohl (hdr->ih_magic) != IH_MAGIC) {printf ("Bad Magic Number\n");SHOW_BOOT_PROGRESS (-10);do_reset (cmdtp, flag, argc, argv);}data = (ulong) & header;len = sizeof (image_header_t);checksum = ntohl (hdr->ih_hcrc);hdr->ih_hcrc = 0;if (crc32 (0, (unsigned char *) data, len) != checksum) {printf ("Bad Header Checksum\n");SHOW_BOOT_PROGRESS (-11);do_reset (cmdtp, flag, argc, argv);}SHOW_BOOT_PROGRESS (10);print_image_hdr (hdr);data = addr + sizeof (image_header_t);len = ntohl (hdr->ih_size);#ifdef CONFIG_HAS_DATAFLASHif (addr_dataflash (addr)) {read_dataflash (data, len, (char *) CFG_LOAD_ADDR);data = CFG_LOAD_ADDR;}#endifif (verify) {ulong csum = 0;printf ("   Verifying Checksum ... ");csum = crc32 (0, (unsigned char *) data, len);if (csum != ntohl (hdr->ih_dcrc)) {printf ("Bad Data CRC\n");SHOW_BOOT_PROGRESS (-12);do_reset (cmdtp, flag, argc, argv);}printf ("OK\n");}SHOW_BOOT_PROGRESS (11);if ((hdr->ih_os != IH_OS_LINUX) ||(hdr->ih_arch != IH_CPU_ARM) ||(hdr->ih_type != IH_TYPE_RAMDISK)) {printf ("No Linux ARM Ramdisk Image\n");SHOW_BOOT_PROGRESS (-13);do_reset (cmdtp, flag, argc, argv);}#if defined(CONFIG_B2) || defined(CONFIG_EVB4510) || defined(CONFIG_ARMADILLO)/**we need to copy the ramdisk to SRAM to let Linux boot*/memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);data = ntohl(hdr->ih_load);#endif /* CONFIG_B2 || CONFIG_EVB4510 *//** Now check if we have a multifile image*/} else if ((hdr->ih_type == IH_TYPE_MULTI) && (len_ptr[1])) {ulong tail = ntohl (len_ptr[0]) % 4;int i;SHOW_BOOT_PROGRESS (13);/* skip kernel length and terminator */data = (ulong) (&len_ptr[2]);/* skip any additional image length fields */for (i = 1; len_ptr; ++i)data += 4;/* add kernel length, and align */data += ntohl (len_ptr[0]);if (tail) {data += 4 - tail;}len = ntohl (len_ptr[1]);} else {/** no initrd image*/SHOW_BOOT_PROGRESS (14);len = data = 0;}#ifdefDEBUGif (!data) {printf ("No initrd\n");}#endifif (data) {initrd_start = data;initrd_end = initrd_start + len;} else {initrd_start = 0;initrd_end = 0;}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_VFD)setup_start_tag (bd);设置各种tag，用于传递参数给Linux#ifdef CONFIG_SERIAL_TAGsetup_serial_tag (¶ms);#endif#ifdef CONFIG_REVISION_TAGsetup_revision_tag (¶ms);#endif#ifdef CONFIG_SETUP_MEMORY_TAGSsetup_memory_tags (bd);#endif#ifdef CONFIG_CMDLINE_TAGsetup_commandline_tag (bd, commandline);#endif#ifdef CONFIG_INITRD_TAGif (initrd_start && initrd_end)setup_initrd_tag (bd, initrd_start, initrd_end);#endif#if defined (CONFIG_VFD) || defined (CONFIG_LCD)setup_videolfb_tag ((gd_t *) gd);#endifsetup_end_tag (bd);#endif/* we assume that the kernel is in place */printf ("\nStarting kernel ...\n\n");打印信息#ifdef CONFIG_USB_DEVICE{extern void udc_disconnect (void);udc_disconnect ();}#endifcleanup_before_linux ();启动之前先做一些清理工作cpu/arm920t/cpu.c调用内核需要传递的参数如下：R0：必须为0R1：机器类型ID，本机为ARM（bd->bi_arch_number）R2：启动参数列表在内存中的位置（bd->bi_boot_params）theKernel (0, bd->bi_arch_number, bd->bi_boot_params);}3.1设置标记ATAG_CORE　　
　　标记列表以标记ATAG_CORE开始
　　



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• static void setup_start_tag (bd_t *bd)
  
• {
  
•     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);//指向当前标记的末尾
  
• }
  

static void setup_start_tag (bd_t *bd){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);//指向当前标记的末尾}3.2设置内存标记ATAG_MEM　　在board/smdk2410/smdk2410.c的dram_init函数设置了bd的bi_dram结构体：
　　



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• int dram_init (void)
  
• {
  
•     gd->bd->bi_dram[0].start = PHYS_SDRAM_1;
  
•     gd->bd->bi_dram[0].size = PHYS_SDRAM_1_SIZE;
  
• 
  
•     return 0;
  
• }
  

int dram_init (void){gd->bd->bi_dram[0].start = PHYS_SDRAM_1;gd->bd->bi_dram[0].size = PHYS_SDRAM_1_SIZE;return 0;}　　
　　下面是这边内存标记的结构体：
　　



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• static void setup_memory_tags (bd_t *bd)
  
• {
  
•     int i;
  
• 
  
•     for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {
  
•         params->hdr.tag = ATAG_MEM;
  
•         params->hdr.size = tag_size (tag_mem32);
  
• 
  
•         params->u.mem.start = bd->bi_dram.start;
  
•         params->u.mem.size = bd->bi_dram.size;
  
• 
  
•         params = tag_next (params);
  
•     }
  
• }
  

static void setup_memory_tags (bd_t *bd){int i;for (i = 0; i < CONFIG_NR_DRAM_BANKS; i++) {params->hdr.tag = ATAG_MEM;params->hdr.size = tag_size (tag_mem32);params->u.mem.start = bd->bi_dram.start;params->u.mem.size = bd->bi_dram.size;params = tag_next (params);}}3.3设置命令行标记ATAG_CMDLINE　　命令行就是一个字符串，用来控制内核的一些行为。比如“root=/dev/mtdblock2 init=/linuxrc console=ttySAC0 ”表示根文件系统在MTD2分区上系统启动后执行的第一个程序为/linuxrc，控制台是ttySAC0 。
　　



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• static void setup_commandline_tag (bd_t *bd, char *commandline)
  
• {
  
•     char *p;
  
• 
  
•     if (!commandline)
  
•         return;
  
• 
  
•     /* eat leading white space */
  
•     for (p = commandline; *p == ' '; p++);
  
• 
  
•     /* skip non-existent command lines so the kernel will still
  
•      * use its default command line.
  
•      */
  
•     if (*p == '\0')
  
•         return;
  
• 
  
•     params->hdr.tag = ATAG_CMDLINE;
  
•     params->hdr.size =
  
•         (sizeof (struct tag_header) + strlen (p) + 1 + 4) >> 2;
  
• 
  
•     strcpy (params->u.cmdline.cmdline, p);
  
• 
  
•     params = tag_next (params);
  
• }
  

static void setup_commandline_tag (bd_t *bd, char *commandline){char *p;if (!commandline)return;/* eat leading white space */for (p = commandline; *p == ' '; p++);/* skip non-existent command lines so the kernel will still* use its default command line.*/if (*p == '\0')return;params->hdr.tag = ATAG_CMDLINE;params->hdr.size =(sizeof (struct tag_header) + strlen (p) + 1 + 4) >> 2;strcpy (params->u.cmdline.cmdline, p);params = tag_next (params);}3.4设置ATAG_NONE　　标记列表以标记ATAG_NONE介绍。
　　



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• static void setup_end_tag (bd_t *bd)
  
• {
  
•     params->hdr.tag = ATAG_NONE;
  
•     params->hdr.size = 0;