Uboot如何添加命令

Uboot如何添加属于自己的一条命令呢？其实doc/README.commands文档中已有详细的说明如下：

Commands are added to U-Boot by creating a new command structure.
This is done by first including command.h

## 通过创建一个新的命令结构体，向U-boot中添加命令。在此之前需要包含头文件

Then using the U_BOOT_CMD() macro to fill in a cmd_tbl_t struct.

## 使用宏函数U_BOOT_CMD()填充一个cmd_tbl_t结构体(查看command.h中的结构体定义)

U_BOOT_CMD(name,maxargs,repeatable,command,"usage","help")

## 该宏函数定义在command.h头文件中

name:     is the name of the commad. THIS IS NOT a string.

# 添加命令的名字，并不是用双引号括起来的字符串。

maxargs: the maximumn numbers of arguments this function takes

# 命令处理函数处理的最大参数个数。

command: Function pointer (*cmd)(struct cmd_tbl_s *, int, int, char *[]);

# 函数指针

usage:     Short description. This is a string

# 该命令简单的使用描述。

help:     long description. This is a string

# 该命令详细的使用说明。

**** Behinde the scene ******

The structure created is named with a special prefix (__u_boot_cmd_)
and placed by the linker in a special section.

## 创建该结构体的变量名称是以(__u_boot_cmd_)为前缀，并添加了

## #define Struct_Section __attribute__ ((unused,section (".u_boot_cmd")))

## 目的是在链接的时候，放到指定的.u_boot_cmd段中。

This makes it possible for the final link to extract all commands
compiled into any object code and construct a static array so the

command can be found in an array starting at __u_boot_cmd_start.

## 定义该结构体变量添加__attribute__属性；使的在链接阶段，

## 把不同的.o文件中定义的命令抽取出来并构造成一个静态数组。

## 而且所有的命令都可以以__u_boot_cmd_start.开始的地址找到

If a new board is defined do not forget to define the command section
by writing in u-boot.lds ($(TOPDIR)/board/boardname/u-boot.lds) these
3 lines:

## 如果一个新版子被定义，

## 在$(TOPDIR)/board/boardname/u-boot.lds链接文件中，请不要忘记添加如下三行内容。

    __u_boot_cmd_start = .;
    .u_boot_cmd : { *(.u_boot_cmd) }

    __u_boot_cmd_end = .;

###########################

#    command.h 头文件内容如下    #

###########################

/* * (C) Copyright 2000-2009 * Wolfgang Denk, DENX Software Engineering, [e-mail]. * * See file CREDITS for list of people who contributed to this * project. * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License as * published by the Free Software Foundation; either version 2 of * the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, * MA 02111-1307 USA *//* *  Definitions for Command Processor */#ifndef __COMMAND_H#define __COMMAND_H#include <config.h>#ifndef NULL#define NULL0#endif/* Default to a width of 8 characters for help message command width */#ifndef CONFIG_SYS_HELP_CMD_WIDTH#define CONFIG_SYS_HELP_CMD_WIDTH8#endif#ifndef__ASSEMBLY__/* * Monitor Command Table */struct cmd_tbl_s {char*name;/* Command Name*/intmaxargs;/* maximum number of arguments*/intrepeatable;/* autorepeat allowed?*//* Implementation function*/int(*cmd)(struct cmd_tbl_s *, int, int, char * const []);char*usage;/* Usage message(short)*/#ifdefCONFIG_SYS_LONGHELPchar*help;/* Help  message(long)*/#endif#ifdef CONFIG_AUTO_COMPLETE/* do auto completion on the arguments */int(*complete)(int argc, char * const argv[], char last_char, int maxv, char *cmdv[]);#endif};typedef struct cmd_tbl_scmd_tbl_t;/* @FeiRan * __u_boot_cmd_start 和 __u_boot_cmd_end符号在 u-boot.lds文件中有定义  */extern cmd_tbl_t  __u_boot_cmd_start;extern cmd_tbl_t  __u_boot_cmd_end;/* common/command.c */int _do_help (cmd_tbl_t *cmd_start, int cmd_items, cmd_tbl_t * cmdtp, int      flag, int argc, char * const argv[]);cmd_tbl_t *find_cmd(const char *cmd);cmd_tbl_t *find_cmd_tbl (const char *cmd, cmd_tbl_t *table, int table_len);extern int cmd_usage(cmd_tbl_t *cmdtp);#ifdef CONFIG_AUTO_COMPLETEextern void install_auto_complete(void);extern int cmd_auto_complete(const char *const prompt, char *buf, int *np, int *colp);#endif/* * Monitor Command * * All commands use a common argument format: * * void function (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[]); */typedefvoidcommand_t (cmd_tbl_t *, int, int, char *[]);#if defined(CONFIG_CMD_MEMORY)\    || defined(CONFIG_CMD_I2C)\    || defined(CONFIG_CMD_ITEST)\    || defined(CONFIG_CMD_PCI)\    || defined(CONFIG_CMD_PORTIO)#define CMD_DATA_SIZEextern int cmd_get_data_size(char* arg, int default_size);#endif#endif/* __ASSEMBLY__ *//* * Command Flags: */#define CMD_FLAG_REPEAT0x0001/* repeat last command*/#define CMD_FLAG_BOOTD0x0002/* command is from bootd*/#define Struct_Section  __attribute__ ((unused,section (".u_boot_cmd")))#ifdef  CONFIG_SYS_LONGHELP#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}#define U_BOOT_CMD_MKENT(name,maxargs,rep,cmd,usage,help) \{#name, maxargs, rep, cmd, usage, help}#else/* no long help info */#define U_BOOT_CMD(name,maxargs,rep,cmd,usage,help) \cmd_tbl_t __u_boot_cmd_##name Struct_Section = {#name, maxargs, rep, cmd, usage}#define U_BOOT_CMD_MKENT(name,maxargs,rep,cmd,usage,help) \{#name, maxargs, rep, cmd, usage}#endif/* CONFIG_SYS_LONGHELP */#if defined(CONFIG_NEEDS_MANUAL_RELOC)void fixup_cmdtable(cmd_tbl_t *cmdtp, int size);#endif#endif/* __COMMAND_H */