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, , 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 < ) {
addr = load_addr;
debug ("* kernel: default image load address = 0x%08lx\n",
load_addr);
} else {
addr = simple_strtoul(argv[], NULL, );
}
//检查内核是否为zImage格式
if (*(ulong *)(addr + *) == 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 = ;
goto after_header_check;
}
#endif
#ifdef CONFIG_NEEDS_MANUAL_RELOC
static int relocated = ;
//重定位启动函数表
/* relocate boot function table */
if (!relocated) {
int i;
for (i = ; i < ARRAY_SIZE(boot_os); i++)
if (boot_os[i] != NULL)
boot_os[i] += gd->reloc_off;
relocated = ;
}
#endif
//判断是否有子命令
/* determine if we have a sub command */
if (argc > ) {
char *endp;
simple_strtoul(argv[], &endp, );
/* 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 != ) && (*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 ;
/*
* 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, );
if (ret < ) {
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 (-);
do_reset (cmdtp, flag, argc, argv);
}
}
if (ret == BOOTM_ERR_UNIMPLEMENTED) {
if (iflag)
enable_interrupts();
show_boot_progress (-);
return ;
}
}
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 ;
}
show_boot_progress ();
#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 (-);
return ;
}
//内核启动前的准备
arch_preboot_os();
//启动内核，不返回
boot_fn(, argc, argv, &images);
show_boot_progress (-);
#ifdef DEBUG
puts ("\n## Control returned to monitor - resetting...\n");
#endif
do_reset (cmdtp, flag, argc, argv);
return ;
}
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, , 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 == ) {
puts ("ERROR: can't get kernel image!\n");
return ;
}
//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 (-);
return ;
}
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 (-);
return ;
}
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 (-);
return ;
}
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 (-);
return ;
}
break;
#endif
default:
puts ("ERROR: unknown image format type!\n");
return ;
}
//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 ;
}
#endif
} else {
puts ("Could not find kernel entry point!\n");
return ;
}
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 ;
} #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 ;
}
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 ;
}
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, , 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 == ) {
puts ("ERROR: can't get kernel image!\n");
return ;
}
//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 (-);
return ;
}
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 (-);
return ;
}
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 (-);
return ;
}
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 (-);
return ;
}
break;
#endif
default:
puts ("ERROR: unknown image format type!\n");
return ;
}
//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 ;
}
#endif
} else {
puts ("Could not find kernel entry point!\n");
return ;
}
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 ;
} #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 ;
}
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 ;
}
#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) != ) {
puts ("GUNZIP: uncompress, out-of-mem or overwrite error "
"- must RESET board to recover\n");
if (boot_progress)
show_boot_progress (-);
return BOOTM_ERR_RESET;
}
*load_end = load + image_len;
break;
#endif /* CONFIG_GZIP */
......
return ;
}
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 != ) && (flag != BOOTM_STATE_OS_GO))
return ;
//从环境变量中获取机器码
s = getenv ("machid");
if (s) {
machid = simple_strtoul (s, NULL, );
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 ();
#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(, machid, bd->bi_boot_params);
/* does not return */
#endif
return ;
}
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 = ;
params->u.core.pagesize = ;
params->u.core.rootdev = ;
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 = ;
}
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[];
};
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 = ;
pCurTag->u.core.pagesize = ;
pCurTag->u.core.rootdev = ; 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++)>>; strcpy(pCurTag->u.cmdline.cmdline,cmdline); pCurTag = tag_next(pCurTag);
}
void setup_end_tag()
{
pCurTag->hdr.tag = ATAG_NONE;
pCurTag->hdr.size = ;
}
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(,,SDRAM_TAGS_START);
printf("qi dong linux nei he"); }