u-boot 内核启动的时候依赖于以下这两行代码：
s = getenv("bootcmd");
...
run_command(s,0);第一条命令是从nand把内核把读到到一个地址上去；第二条命令是从内核里面启动内核；
从哪里读？从kernel分区读；
读到哪里去？放到指定地址(0x30007fc0)去；
在PC机上，每一个硬盘前面都有一个分区表。对于嵌入式Linux来说，flash上面没有分区表，显然这个分区就和PC机上不一样；既然没有分区表，这些分区怎么体现？只能在源码里面写死的；
定义分区的源码如下：
#define MTDPARTS_DEFAULT "mtdparts=nandflash0:256K@0(bootloader),"\也即从0到256K为bootloader
"128k(params),"\接下来的128K放的是uboot的环境变量
"2m(kernel),"\ 2M空间放的是kernel
"-(root)" 剩下的是root分区上面定义了各个分区的起始地址；
具体地址从uboot菜单中输入mtd命令即可。下面的这个图是我的四个分区：
所以 nand read.jffs2 0x30007fc0 kernel = nand read.jffs2 0x30007fc0 0x00060000 0x0x00200000
下面分析一下如何读，如何把2M的内核读到0x30007fc0处？
因为启动时do_bootm，所以可以猜测nand read 应该是do_nand函数,do_nand函数代码如下：
int do_nand(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])
{
int i, dev, ret;
ulong addr, off, size;
char *cmd, *s;
nand_info_t *nand;
int quiet = 0;
const char *quiet_str = getenv("quiet");
/* at least two arguments please */
if (argc < 2)
goto usage;
if (quiet_str)
quiet = simple_strtoul(quiet_str, NULL, 0) != 0;
cmd = argv[1];
if (strcmp(cmd, "info") == 0) {
putc('\n');
for (i = 0; i < CFG_MAX_NAND_DEVICE; i++) {
if (nand_info[i].name)
printf("Device %d: %s, sector size %lu KiB\n",
i, nand_info[i].name,
nand_info[i].erasesize >> 10);
}
return 0;
}
if (strcmp(cmd, "device") == 0) {
if (argc < 3) {
if ((nand_curr_device < 0) ||
(nand_curr_device >= CFG_MAX_NAND_DEVICE))
puts("\nno devices available\n");
else
printf("\nDevice %d: %s\n", nand_curr_device,
nand_info[nand_curr_device].name);
return 0;
}
dev = (int)simple_strtoul(argv[2], NULL, 10);
if (dev < 0 || dev >= CFG_MAX_NAND_DEVICE || !nand_info[dev].name) {
puts("No such device\n");
return 1;
}
printf("Device %d: %s", dev, nand_info[dev].name);
puts("... is now current device\n");
nand_curr_device = dev;
#ifdef CFG_NAND_SELECT_DEVICE
/* * Select the chip in the board/cpu specific driver */
board_nand_select_device(nand_info[dev].priv, dev);
#endif
return 0;
}
if (strcmp(cmd, "bad") != 0 && strcmp(cmd, "erase") != 0 &&
strncmp(cmd, "dump", 4) != 0 &&
strncmp(cmd, "read", 4) != 0 && strncmp(cmd, "write", 5) != 0 &&
strcmp(cmd, "scrub") != 0 && strcmp(cmd, "markbad") != 0 &&
strcmp(cmd, "biterr") != 0 &&
strcmp(cmd, "lock") != 0 && strcmp(cmd, "unlock") != 0 )
goto usage;
/* the following commands operate on the current device */
if (nand_curr_device < 0 || nand_curr_device >= CFG_MAX_NAND_DEVICE ||
!nand_info[nand_curr_device].name) {
puts("\nno devices available\n");
return 1;
}
nand = &nand_info[nand_curr_device];
if (strcmp(cmd, "bad") == 0) {
printf("\nDevice %d bad blocks:\n", nand_curr_device);
for (off = 0; off < nand->size; off += nand->erasesize)
if (nand_block_isbad(nand, off))
printf(" %08x\n", off);
return 0;
}
/* * Syntax is: * 0 1 2 3 4 * nand erase [clean] [off size] */
if (strcmp(cmd, "erase") == 0 || strcmp(cmd, "scrub") == 0) {
nand_erase_options_t opts;
/* "clean" at index 2 means request to write cleanmarker */
int clean = argc > 2 && !strcmp("clean", argv[2]);
int o = clean ? 3 : 2;
int scrub = !strcmp(cmd, "scrub");
printf("\nNAND %s: ", scrub ? "scrub" : "erase");
/* skip first two or three arguments, look for offset and size */
if (arg_off_size(argc - o, argv + o, nand, &off, &size) != 0)
return 1;
memset(&opts, 0, sizeof(opts));
opts.offset = off;
opts.length = size;
opts.jffs2 = clean;
opts.quiet = quiet;
if (scrub) {
puts("Warning: "
"scrub option will erase all factory set "
"bad blocks!\n"
" "
"There is no reliable way to recover them.\n"
" "
"Use this command only for testing purposes "
"if you\n"
" "
"are sure of what you are doing!\n"
"\nReally scrub this NAND flash? <y/N>\n");
if (getc() == 'y' && getc() == '\r') {
opts.scrub = 1;
} else {
puts("scrub aborted\n");
return -1;
}
}
ret = nand_erase_opts(nand, &opts);
printf("%s\n", ret ? "ERROR" : "OK");
return ret == 0 ? 0 : 1;
}
if (strncmp(cmd, "dump", 4) == 0) {
if (argc < 3)
goto usage;
s = strchr(cmd, '.');
off = (int)simple_strtoul(argv[2], NULL, 16);
if (s != NULL && strcmp(s, ".oob") == 0)
ret = nand_dump_oob(nand, off);
else
ret = nand_dump(nand, off);
return ret == 0 ? 1 : 0;
}
/* read write */
if (strncmp(cmd, "read", 4) == 0 || strncmp(cmd, "write", 5) == 0) {
int read;
if (argc < 4)
goto usage;
addr = (ulong)simple_strtoul(argv[2], NULL, 16);
read = strncmp(cmd, "read", 4) == 0; /* 1 = read, 0 = write */
printf("\nNAND %s: ", read ? "read" : "write");
if (arg_off_size(argc - 3, argv + 3, nand, &off, &size) != 0)
return 1;
s = strchr(cmd, '.');
if (s != NULL &&
(!strcmp(s, ".jffs2") || !strcmp(s, ".e") || !strcmp(s, ".i"))) {
if (read) {
/* read */
nand_read_options_t opts;
memset(&opts, 0, sizeof(opts));
opts.buffer = (u_char*) addr;
opts.length = size;
opts.offset = off;
opts.quiet = quiet;
ret = nand_read_opts(nand, &opts);
} else {
/* write */
nand_write_options_t opts;
memset(&opts, 0, sizeof(opts));
opts.buffer = (u_char*) addr;
opts.length = size;
opts.offset = off;
/* opts.forcejffs2 = 1; */
opts.pad = 1;
opts.blockalign = 1;
opts.quiet = quiet;
ret = nand_write_opts(nand, &opts);
}
} else {
if (read)
ret = nand_read(nand, off, &size, (u_char *)addr);
else
ret = nand_write(nand, off, &size, (u_char *)addr);
}
printf(" %d bytes %s: %s\n", size,
read ? "read" : "written", ret ? "ERROR" : "OK");
return ret == 0 ? 0 : 1;
}
if (strcmp(cmd, "markbad") == 0) {
addr = (ulong)simple_strtoul(argv[2], NULL, 16);
int ret = nand->block_markbad(nand, addr);
if (ret == 0) {
printf("block 0x%08lx successfully marked as bad\n",
(ulong) addr);
return 0;
} else {
printf("block 0x%08lx NOT marked as bad! ERROR %d\n",
(ulong) addr, ret);
}
return 1;
}
if (strcmp(cmd, "biterr") == 0) {
/* todo */
return 1;
}
if (strcmp(cmd, "lock") == 0) {
int tight = 0;
int status = 0;
if (argc == 3) {
if (!strcmp("tight", argv[2]))
tight = 1;
if (!strcmp("status", argv[2]))
status = 1;
}
if (status) {
ulong block_start = 0;
ulong off;
int last_status = -1;
struct nand_chip *nand_chip = nand->priv;
/* check the WP bit */
nand_chip->cmdfunc (nand, NAND_CMD_STATUS, -1, -1);
printf("device is %swrite protected\n",
(nand_chip->read_byte(nand) & 0x80 ?
"NOT " : "" ) );
for (off = 0; off < nand->size; off += nand->oobblock) {
int s = nand_get_lock_status(nand, off);
/* print message only if status has changed * or at end of chip */
if (off == nand->size - nand->oobblock
|| (s != last_status && off != 0)) {
printf("%08x - %08x: %8d pages %s%s%s\n",
block_start,
off-1,
(off-block_start)/nand->oobblock,
((last_status & NAND_LOCK_STATUS_TIGHT) ? "TIGHT " : ""),
((last_status & NAND_LOCK_STATUS_LOCK) ? "LOCK " : ""),
((last_status & NAND_LOCK_STATUS_UNLOCK) ? "UNLOCK " : ""));
}
last_status = s;
}
} else {
if (!nand_lock(nand, tight)) {
puts("NAND flash successfully locked\n");
} else {
puts("Error locking NAND flash\n");
return 1;
}
}
return 0;
}
if (strcmp(cmd, "unlock") == 0) {
if (arg_off_size(argc - 2, argv + 2, nand, &off, &size) < 0)
return 1;
if (!nand_unlock(nand, off, size)) {
puts("NAND flash successfully unlocked\n");
} else {
puts("Error unlocking NAND flash, "
"write and erase will probably fail\n");
return 1;
}
return 0;
}
usage:
printf("Usage:\n%s\n", cmdtp->usage);
return 1;
}
u-boot 在flash上的存储的内核称为uImage,uimage的格式：头部+真正的内核； 头部主要有:
in-load:加载地址，表示运行内核的时候，内核应该先将其放到哪里；
in_ep:入口地址，表示要运行内核的时候，直接跳到这个地址就可以了；
下面要开始分析如何启动内核,主要是do_bootm函数:
int do_bootm (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
{
ulong iflag;
ulong addr;
ulong data, len, checksum;
ulong *len_ptr;
uint unc_len = CFG_BOOTM_LEN;
int i, verify;
char *name, *s;
int (*appl)(int, char *[]);
image_header_t *hdr = &header;
注释开始
这里就是uimage的头部，是一个结构体
typedef struct image_header {
uint32_t ih_magic;
uint32_t ih_hcrc;
uint32_t ih_time;
uint32_t ih_size;
uint32_t ih_load; 表示内核运行的时候你要把它放在哪里。
uint32_t ih_ep; 运行内核的时候入口地址，之前设置的是0x30007fc0，只要不破坏uboot内存使用分配即可，因为sp后面还有几十M的空间。正是因为uimage中有个header，header结构体中有一个loadaddress。我们把uimage放在某个地址，bootm加上这个地址，去读出头部中的in_load，如果发现内核不在加载地址中，则需要把内核移动到这个加载地址中去，最后跳到in_ep去执行。
uint32_t ih_dcrc;
uint8_t ih_os;
uint8_t ih_arch;
uint8_t ih_type;
uint8_t ih_comp;
uint8_t ih_name[IH_NMLEN];
} image_header_t;
注释结束
s = getenv ("verify");
verify = (s && (*s == 'n')) ? 0 : 1;
if (argc < 2) {
addr = load_addr;
} else {
addr = simple_strtoul(argv[1], NULL, 16);
}
SHOW_BOOT_PROGRESS (1);
printf ("## Booting image at lx ...\n", addr);
#ifdef CONFIG_HAS_DATAFLASH
if (addr_dataflash(addr)){
read_dataflash(addr, sizeof(image_header_t), (char *)&header);
} else
#endif
memmove (&header, (char *)addr, sizeof(image_header_t));
if (ntohl(hdr->ih_magic) != IH_MAGIC) {
#ifdef __I386__
if (fake_header(hdr, (void*)addr, -1) != NULL) {
addr -= sizeof(image_header_t);
verify = 0;
} else
#endif
{
puts ("Bad Magic Number\n");
SHOW_BOOT_PROGRESS (-1);
return 1;
}
}
SHOW_BOOT_PROGRESS (2);
data = (ulong)&header;
len = sizeof(image_header_t);
checksum = ntohl(hdr->ih_hcrc);
hdr->ih_hcrc = 0;
if (crc32 (0, (uchar *)data, len) != checksum) {
puts ("Bad Header Checksum\n");
SHOW_BOOT_PROGRESS (-2);
return 1;
}
SHOW_BOOT_PROGRESS (3);
#ifdef CONFIG_HAS_DATAFLASH
if (addr_dataflash(addr)){
len = ntohl(hdr->ih_size) + sizeof(image_header_t);
read_dataflash(addr, len, (char *)CFG_LOAD_ADDR);
addr = CFG_LOAD_ADDR;
}
#endif
print_image_hdr ((image_header_t *)addr);
data = addr + sizeof(image_header_t);
len = ntohl(hdr->ih_size);
if (verify) {
puts (" Verifying Checksum ... ");
if (crc32 (0, (uchar *)data, len) != ntohl(hdr->ih_dcrc)) {
printf ("Bad Data CRC\n");
SHOW_BOOT_PROGRESS (-3);
return 1;
}
puts ("OK\n");
}
SHOW_BOOT_PROGRESS (4);
len_ptr = (ulong *)data;
#if defined(__PPC__)
if (hdr->ih_arch != IH_CPU_PPC)
#elif defined(__ARM__)
if (hdr->ih_arch != IH_CPU_ARM)
#elif defined(__I386__)
if (hdr->ih_arch != IH_CPU_I386)
#elif defined(__mips__)
if (hdr->ih_arch != IH_CPU_MIPS)
#elif defined(__nios__)
if (hdr->ih_arch != IH_CPU_NIOS)
#elif defined(__M68K__)
if (hdr->ih_arch != IH_CPU_M68K)
#elif defined(__microblaze__)
if (hdr->ih_arch != IH_CPU_MICROBLAZE)
#elif defined(__nios2__)
if (hdr->ih_arch != IH_CPU_NIOS2)
#elif defined(__blackfin__)
if (hdr->ih_arch != IH_CPU_BLACKFIN)
#elif defined(__avr32__)
if (hdr->ih_arch != IH_CPU_AVR32)
#else
# error Unknown CPU type
#endif
{
printf ("Unsupported Architecture 0x%x\n", hdr->ih_arch);
SHOW_BOOT_PROGRESS (-4);
return 1;
}
SHOW_BOOT_PROGRESS (5);
switch (hdr->ih_type) {
case IH_TYPE_STANDALONE:
name = "Standalone Application";
if (argc > 2) {
hdr->ih_load = htonl(simple_strtoul(argv[2], NULL, 16));
}
break;
case IH_TYPE_KERNEL:
name = "Kernel Image";
break;
case IH_TYPE_MULTI:
name = "Multi-File Image";
len = ntohl(len_ptr[0]);
data += 8;
for (i=1; len_ptr[i]; ++i)
data += 4;
break;
default: printf ("Wrong Image Type for %s command\n", cmdtp->name);
SHOW_BOOT_PROGRESS (-5);
return 1;
}
SHOW_BOOT_PROGRESS (6);
iflag = disable_interrupts();
#ifdef CONFIG_AMIGAONEG3SE
icache_disable();
invalidate_l1_instruction_cache();
flush_data_cache();
dcache_disable();
#endif
switch (hdr->ih_comp) {
case IH_COMP_NONE:
if(ntohl(hdr->ih_load) == addr) {如果ih_load==addr，则打印xip
printf (" XIP %s ... ", name);
} else {
#if defined(CONFIG_HW_WATCHDOG) || defined(CONFIG_WATCHDOG)
size_t l = len;
void *to = (void *)ntohl(hdr->ih_load);
void *from = (void *)data;
printf (" Loading %s ... ", name);
while (l > 0) {
size_t tail = (l > CHUNKSZ) ? CHUNKSZ : l;
WATCHDOG_RESET();
memmove (to, from, tail);
to += tail;
from += tail;
l -= tail;
}
#else 否则就要移动真正的内核
memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);这里就是把真正内核开始的data移动到ih_load加载地址中去。韦东山开发板的内核真正地址为0x30008000，而内核头部的起始地址是0x30007fc0，两者相差64字节，正好是头部的长度，这样就不用做搬运真正的内核的工作了。可以加快启动速度。
#endif
}
break;
case IH_COMP_GZIP:
printf (" Uncompressing %s ... ", name);
if (gunzip ((void *)ntohl(hdr->ih_load), unc_len,
(uchar *)data, &len) != 0) {
puts ("GUNZIP ERROR - must RESET board to recover\n");
SHOW_BOOT_PROGRESS (-6);
do_reset (cmdtp, flag, argc, argv);
}
break;
#ifdef CONFIG_BZIP2
case IH_COMP_BZIP2:
printf (" Uncompressing %s ... ", name);
i = BZ2_bzBuffToBuffDecompress ((char*)ntohl(hdr->ih_load),
&unc_len, (char *)data, len,
CFG_MALLOC_LEN < (4096 * 1024), 0);
if (i != BZ_OK) {
printf ("BUNZIP2 ERROR %d - must RESET board to recover\n", i);
SHOW_BOOT_PROGRESS (-6);
udelay(100000);
do_reset (cmdtp, flag, argc, argv);
}
break;
#endif
default:
if (iflag)
enable_interrupts();
printf ("Unimplemented compression type %d\n", hdr->ih_comp);
SHOW_BOOT_PROGRESS (-7);
return 1;
}
puts ("OK\n");
SHOW_BOOT_PROGRESS (7);
switch (hdr->ih_type) {
case IH_TYPE_STANDALONE:
if (iflag)
enable_interrupts();
if (((s = getenv("autostart")) != NULL) && (strcmp(s,"no") == 0)) {
char buf[32];
sprintf(buf, "%lX", len);
setenv("filesize", buf);
return 0;
}
appl = (int (*)(int, char *[]))ntohl(hdr->ih_ep);
(*appl)(argc-1, &argv[1]);
return 0;
case IH_TYPE_KERNEL:
case IH_TYPE_MULTI:
break;
default:
if (iflag)
enable_interrupts();
printf ("Can't boot image type %d\n", hdr->ih_type);
SHOW_BOOT_PROGRESS (-8);
return 1;
}
SHOW_BOOT_PROGRESS (8);
switch (hdr->ih_os) {
default:
case IH_OS_LINUX:
#ifdef CONFIG_SILENT_CONSOLE
fixup_silent_linux();
#endif
do_bootm_linux (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
case IH_OS_NETBSD:
do_bootm_netbsd (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#ifdef CONFIG_LYNXKDI
case IH_OS_LYNXOS:
do_bootm_lynxkdi (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#endif
case IH_OS_RTEMS:
do_bootm_rtems (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#if (CONFIG_COMMANDS & CFG_CMD_ELF)
case IH_OS_VXWORKS:
do_bootm_vxworks (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
case IH_OS_QNX:
do_bootm_qnxelf (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#endif
#ifdef CONFIG_ARTOS
case IH_OS_ARTOS:
do_bootm_artos (cmdtp, flag, argc, argv,
addr, len_ptr, verify);
break;
#endif
}
SHOW_BOOT_PROGRESS (-9);
#ifdef DEBUG
puts ("\n## Control returned to monitor - resetting...\n");
do_reset (cmdtp, flag, argc, argv);
#endif
return 1;
}do_bootm有两个作用：
作用1：读取内核头部将内核移动到合适地方，还有一些校验
作用2：启动内核，用的是do_bootm_linux函数。在跳到ih_ep入口之前还要uboot设置内核启动参数，然后才是跳到ih_ep启动内核。
do_bootm_linux函数开始的代码如下：
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);
if (argc >= 3) {
SHOW_BOOT_PROGRESS (9);
addr = simple_strtoul (argv[2], NULL, 16);
printf ("## Loading Ramdisk Image at lx ...\n", addr);
#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)
memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
data = ntohl(hdr->ih_load);
#endif
} else if ((hdr->ih_type == IH_TYPE_MULTI) && (len_ptr[1])) {
ulong tail = ntohl (len_ptr[0]) % 4;
int i;
SHOW_BOOT_PROGRESS (13);
data = (ulong) (&len_ptr[2]);
for (i = 1; len_ptr[i]; ++i)
data += 4;
data += ntohl (len_ptr[0]);
if (tail) {
data += 4 - tail;
}
len = ntohl (len_ptr[1]);
} else {
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 lx) ...\n",
(ulong) theKernel);
#if defined (CONFIG_SETUP_MEMORY_TAGS) || \ uboot设置参数在这里
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);
#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
printf ("\nStarting kernel ...\n\n");
#ifdef CONFIG_USB_DEVICE
{
extern void udc_disconnect (void);
udc_disconnect ();
}
#endif
cleanup_before_linux ();
theKernel (0, bd->bi_arch_number, bd->bi_boot_params);启动内核在这里
}do_bootm_linux
作用1：设置内核启动参数，参数的格式是tag，对于韦东山的开发板地址是0x30000100，下面分析两个参数，其中setup_start_tag和setup_end_tag是必须的。
static void setup_start_tag (bd_t *bd)
{
params = (struct tag *) bd->bi_boot_params;bi_boot_params在代码中搜索发现是
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);
}作用2：跳到入口地址去是
theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
theKernel (0, bd->bi_arch_number, bd->bi_boot_params);
这样就启动内核了！！！
具体bi_boot_params是多少搜索代码可以知道，其实韦东山是在自己的100ask24x0.c中自己定义的。
setup_start_tag之后我们得到：
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);
}0x30000100|size|tag|flag|page_size|root_dev|
其中header_size=sizeof(struct tag_header) + (sizeof(struct type) >> 2)
也就是说执行完这个函数之后，要明白在内核启动参数区域都放了大小是多少的参数。
执行完setup_memory_tag函数之后：
#ifdef CONFIG_SETUP_MEMORY_TAGS
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[i].start;
params->u.mem.size = bd->bi_dram[i].size;
params = tag_next (params);
}
}
#endif这时存储内核启动参数的区域类似于setup_start_tag
开始是size|tag|size|start|
下面是start_commandline_tag
static void setup_commandline_tag (bd_t *bd, char *commandline)
{
char *p;
if (!commandline)
return;
把命令前面的空格给干掉
for (p = commandline; *p == ' '; p++);
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);
}commandline被传入一个参数*commandline，而这个参数是getev(“bootargs”),用print命令在uboot命令行中查看bootargs，其中包括了内核的console的信息从哪里打印出来，是同ttyssa0也即串口0打出来。
size|tag|bootargs
最后一个是setup_end_tag-
static void setup_end_tag (bd_t *bd)
{
params->hdr.tag = ATAG_NONE;
params->hdr.size = 0;
}这两个参数全是0。