uboot命令的实现
先分一下，uboot如何解析我们输进去的命令，其中argv[x]就是用来保存每一条指令，uboot支持多条命令一起输入，用分号;隔开
/* Extract arguments */
if ((argc = parse_line (finaltoken, argv)) == 0) {
rc = -1; /* no command at all */
continue;
}
然后是在表中查找是否有输入的命令，后续还要做一些命令合格性的检查
/* Look up command in command table */
if ((cmdtp = find_cmd(argv[0])) == NULL) {
printf ("Unknown command '%s' - try 'help'\n", argv[0]);
rc = -1; /* give up after bad command */
continue;
}
/* found - check max args */
if (argc > cmdtp->maxargs) {
printf ("Usage:\n%s\n", cmdtp->usage);
rc = -1;
continue;
}
其中有个结构体需要注意，每个命令，都有一个名字，还有对应的参数，以及执行命令的函数，这些都被打包放在一起结构体变量中
struct cmd_tbl_s {
char *name; /* Command Name */
int maxargs; /* maximum number of arguments */
int repeatable; /* autorepeat allowed? */
/* Implementation function */
int (*cmd)(struct cmd_tbl_s *, int, int, char *[]);
char *usage; /* Usage message (short) */
#ifdef CFG_LONGHELP
char *help; /* Help message (long) */
#endif
#ifdef CONFIG_AUTO_COMPLETE
/* do auto completion on the arguments */
int (*complete)(int argc, char *argv[], char last_char, int maxv, char *cmdv[]);
#endif
};
在find_cmd中，通过一个for循环去找命令是否存在
for (cmdtp = &__u_boot_cmd_start;
cmdtp != &__u_boot_cmd_end;
cmdtp++) {
if (strncmp (cmd, cmdtp->name, len) == 0) {
if (len == strlen (cmdtp->name))
return cmdtp; /* full match */
cmdtp_temp = cmdtp; /* abbreviated command ? */
n_found++;
}
}
其中__u_boot_cmd_start和__u_boot_cmd_end是在链接脚本中指定的
. = .;
__u_boot_cmd_start = .;
.u_boot_cmd : { *(.u_boot_cmd) }
__u_boot_cmd_end = .;
再看一下u_boot_cmd这个段到底是干嘛的，可以找到两个宏定义，第一个定义了一个段，第二个在执行命令时进行宏展开
#define Struct_Section __attribute__ ((unused,section (".u_boot_cmd")))
#define U_BOOT_CMD(name,maxargs,rep,cmd,usage,help) \
cmd_tbl_t __u_boot_cmd_##name Struct_Section = {#name, maxargs, rep, cmd, usage, help}
如果现在执行bootm 0x30007FC0，看看跟宏U_BOOT_CMD有什么关系
U_BOOT_CMD(
bootm, CFG_MAXARGS, 1, do_bootm,
"bootm - boot application image from memory\n",
"[addr [arg ...]]\n - boot application image stored in memory\n"
"\tpassing arguments 'arg ...'; when booting a Linux kernel,\n"
"\t'arg' can be the address of an initrd image\n"
#ifdef CONFIG_OF_FLAT_TREE
"\tWhen booting a Linux kernel which requires a flat device-tree\n"
"\ta third argument is required which is the address of the of the\n"
"\tdevice-tree blob. To boot that kernel without an initrd image,\n"
"\tuse a '-' for the second argument. If you do not pass a third\n"
"\ta bd_info struct will be passed instead\n"
#endif
);
展开后，发现是定义了一个cmd_tbl_t类型的结构体变量__u_boot_cmd_bootm，后面的Struct_Section也宏展开，发现段属性被强制设为u_boot_cmd段
cmd_tbl_t __u_boot_cmd_bootm Struct_Section = {"bootm", CFG_MAXARGS, 1, do_bootm, usage, help}
Struct_Section __attribute__ ((unused,section (".u_boot_cmd")))
这里面的usage和help，是替换上面的字符串，其中
- usage：“bootm - boot application image from memory\n”
- help：剩下的所有字符串
可以发现usage替换的后面是有逗号的，help的字符串双引号之间没有任何间隔符号
接下来自己写一个命令试试看，在common目录下创建文件cmd_hello.c
#include <common.h>
#include <watchdog.h>
#include <command.h>
#include <image.h>
#include <malloc.h>
#include <zlib.h>
#include <bzlib.h>
#include <environment.h>
#include <asm/byteorder.h>
int do_hello (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
{
printf("hello world uboot sb things\n");
}
U_BOOT_CMD(
hello, CFG_MAXARGS, 1, do_hello,
"hello - this is a first uboot cmd, hello world\n",
"this is a infomation for help, long string"
);
修改command目录下的Makefile文件，增加一个源文件cmd_hello.o，编译烧录即可
uboot启动内核
通过之前的分析，可以知道，内核是由bootm启动，所以接下来分析整个bootcmd命令的参数
s = getenv ("bootcmd");
printf("Booting Linux ...\n");
run_command (s, 0);
这条命令，第一句话，将内核从kernel分区读出，并放到SDRAM的指定地址，然后从这个地址启动内核
bootcmd=nand read.jffs2 0x30007FC0 kernel; bootm 0x30007FC0
在uboot中，一般会将分区大小写死
#define MTDPARTS_DEFAULT "mtdparts=nandflash0:256k@0(bootloader)," \
"128k(params)," \
"2m(kernel)," \
"-(root)"
所以第一句话等价于下面的，从0x00060000读取内核，大小为0x00200000，存放到0x30007FC0
bootcmd=nand read.jffs2 0x30007FC0 kernel;
bootcmd=nand read.jffs2 0x30007FC0 0x00060000 0x00200000;
接下来看如何从nand中读取内核，重点在于nand_read_opts
int do_nand(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[])
{
...
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);
}
...
}
读出了内核后，接下来如何启动，分析bootm
bootm 0x30007FC0
首先分析一下uImage的结构，它是一个64字节的头部+真正的内核组成，其中有两项比较重要的参数
ih_load加载地址和ih_ep入口地址
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;
bootm命令先去读取uImage的头部信息，如果发现当前内核并不位于它指定的加载地址，就将内核移到指定的加载地址，然后uboot需要告诉内核一些启动参数，这些参数是存放到某些地址，然后内核去这些地址去读取对应的参数，就是所谓的tag，参数传完后，跳转到入口地址执行
memmove (&header, (char *)addr, sizeof(image_header_t));
memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len);
do_bootm_linux(...);
setup_start_tag (bd); //设置参数
setup_serial_tag (¶ms);
setup_revision_tag (¶ms);
setup_memory_tags (bd);
setup_commandline_tag (bd, commandline);
等等
theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep);
theKernel (0, bd->bi_arch_number, bd->bi_boot_params); //启动内核
启动内核时传递了三个参数，其中bd->bi_arch_number是机器ID，bd->bi_boot_params是传递的参数地址