GT2440--U-Boot分析（四）
run_command()分析：
int run_command (const char *cmd, int flag)
{
cmd_tbl_t *cmdtp;
char cmdbuf[CFG_CBSIZE]; /* working copy of cmd */
char *token; /* start of token in cmdbuf */
char *sep; /* end of token (separator) in cmdbuf */
char finaltoken[CFG_CBSIZE];
char *str = cmdbuf;
char *argv[CFG_MAXARGS + 1]; /* NULL terminated */
int argc, inquotes;
int repeatable = 1;
int rc = 0;
clear_ctrlc(); /* forget any previous Control C */
if (!cmd || !*cmd) {
return -1; /* empty command */
}
if (strlen(cmd) >= CFG_CBSIZE) {
puts ("## Command too long!\n");
return -1;
}
strcpy (cmdbuf, cmd);
while (*str) {
/*
* Find separator, or string end
* Allow simple escape of ';' by writing "\;"
*/
for (inquotes = 0, sep = str; *sep; sep++) {
if ((*sep=='\'') &&
(*(sep-1) != '\\'))
inquotes=!inquotes;
if (!inquotes &&
(*sep == ';') && /* separator */
( sep != str) && /* past string start */
(*(sep-1) != '\\')) /* and NOT escaped */
break;
}
/*
* Limit the token to data between separators
*/
token = str;
if (*sep) {
str = sep + 1; /* start of command for next pass */
*sep = '\0';
}
else
str = sep; /* no more commands for next pass */
/* find macros in this token and replace them */
process_macros (token, finaltoken);
/* Extract arguments */
if ((argc = parse_line (finaltoken, argv)) == 0) {
rc = -1; /* no command at all */
continue;
}
/* 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;
}
#if (CONFIG_COMMANDS & CFG_CMD_BOOTD)
/* avoid "bootd" recursion */
if (cmdtp->cmd == do_bootd) {
if (flag & CMD_FLAG_BOOTD) {
puts ("'bootd' recursion detected\n");
rc = -1;
continue;
} else {
flag |= CMD_FLAG_BOOTD;
}
}
#endif /* CFG_CMD_BOOTD */
/* OK - call function to do the command */
if ((cmdtp->cmd) (cmdtp, flag, argc, argv) != 0) {
rc = -1;
}
repeatable &= cmdtp->repeatable;
/* Did the user stop this? */
if (had_ctrlc ())
return 0; /* if stopped then not repeatable */
}
return rc ? rc : repeatable;
}
上述代码为删减后的run_command()函数代码并不是很难，且代码中有着较为详细的注释。其中应注意如下两句代码：
if ((cmdtp = find_cmd(argv[0])) == NULL) /* 在u_boot_com数据段下查询是否有这个指令 */
if ((cmdtp->cmd) (cmdtp, flag, argc, argv) != 0) /* 调用实现该指令的函数 */
下面进行find_cmd()函数的分析，这函数相对较为简短；
cmd_tbl_t *find_cmd (const char *cmd)
{
cmd_tbl_t *cmdtp;
cmd_tbl_t *cmdtp_temp = &__u_boot_cmd_start; /*Init value */
const char *p;
int len;
int n_found = 0;
/*
* Some commands allow length modifiers (like "cp.b");
* compare command name only until first dot.
*/
len = ((p = strchr(cmd, '.')) == NULL) ? strlen (cmd) : (p - cmd);
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++;
}
}
if (n_found == 1) { /* exactly one match */
return cmdtp_temp;
}
return NULL; /* not found or ambiguous command */
}
重点留意如下代码：
1、cmd_tbl_t结构体：
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
};
typedef struct cmd_tbl_s cmd_tbl_t;
2、查询u_boot_cmd数据段的for循环寻找合适的指令
for (cmdtp = &__u_boot_cmd_start; cmdtp != &__u_boot_cmd_end; cmdtp++)
要查询此数据段那则次数据段必须建立一组命令表,通过如下步骤建立这个表：
一、添加结构体定义
U_BOOT_CMD( menu, 3, 0, do_menu, "menu - display a menu, to select the items to do something\n", " - display a menu, to select the items to do something" );
二、此命令的实现函数
int do_menu (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
{
menu_shell();
return 0;
}
其中上面循环中使用到的__u_boot_cmd_start与__u_boot_cmd_end均定义在u_boot.lds连接脚本中；
cmdtp = &__u_boot_cmd_start; /* u_boot_cmd数据段的__u_boot_cmd_start地址的内容取出存放至cmdtp中 */
此时进行.u_boot_cmd数据段查询的如下代码：
#define Struct_Section __attribute__ ((unused,section (".u_boot_cmd")))
并得到如下的宏定义：
#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}
例如增加一个toraloo命令，则上述宏可展开为：
cmd_tbl_t __u_boot_cmd_toraloo Struct_Section = {“toraloo”, 3, 1, do_toraloo, “string 1”, “string 2”};
toraloo命令可仿照menu命令编写如：
U_BOOT_CMD(
toraloo 3, 1, do_toraloo,
"toraloo - I am toraloo,HAHAHA.......\n",
" TORALOO is toraloo,ToraLoo is toraloo"
);
int do_menu (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
{
int i;
printf(“this is a test! %d\n”,argc);
for(i=0; i<argc; i++)
{
printf(“argv[%d] = %s\n”,i,argv[i]);
}
return 0;
}
再此文件中添加部分头文件，在对/command/makefile下增加cmd_toraloo.o的编译项重新再编译一次u-boot，再将其下载即可看见toraloo这个命令了。
U-boot下的内核启动命令：bootm
输入bootm运行时相当于运行了bootcmd，其将会调度do_bootm()完成命令的功能在do_bootm(...)中再调度do_bootm_linux(....)完成内的内核启动前的设定与硬件参数的设定（如SDRAM地址大小等信息...）最终通过如下两句话实现内核的启动：
theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep); theKernel (0, bd->bi_arch_number, bd->bi_boot_params);
（PS：还有注意一下关于镜像文件头结构体：
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;
这种留意如下三个参数：
uint32_t ih_size; /* Image Data Size */
uint32_t ih_load; /* Data Load Address */
uint32_t ih_ep; /* Entry Point Address */
）