Linux系统环境搭建

对uboot、Linux、rootfs的深刻理解
uboot2012改进：
学习使用cmd,添加cmd_menu.c
了解U_BOOT_CMD的用法：
    #define U_BOOT_CMD(name,maxargs,rep,cmd,usage,help) \
      U_BOOT_CMD_COMPLETE(name,maxargs,rep,cmd,usage,help,NULL)
     
   #define U_BOOT_CMD_COMPLETE(name,maxargs,rep,cmd,usage,help,comp) \
      cmd_tbl_t __u_boot_cmd_##name Struct_Section = \
  U_BOOT_CMD_MKENT_COMPLETE(name,maxargs,rep,cmd,usage,help,comp)
   
    #define U_BOOT_CMD_MKENT_COMPLETE(name,maxargs,rep,cmd,usage,help,comp) \
  {#name, maxargs, rep, cmd, usage, _CMD_HELP(help) _CMD_COMPLETE(comp)}
 
U_BOOT_CMD(name,maxargs,rep,cmd,usage,help)
1 name  命令的名字
2 maxargs  最大命令行参数个数
3 rep
4 cmd   命令
5 usage 用法
6 帮助

其实我们只关心前面4个宏参数,U_BOOT_CMD的最终定义是这样的：
#define U_BOOT_CMD(name,maxargs,rep,cmd,usage,help) cmd_tbl_t __u_boot_cmd_##name Struct_Section = \
 {#name, maxargs, rep, cmd, usage, _CMD_HELP(help) _CMD_COMPLETE(comp)}
 
 比如：
  U_BOOT_CMD(
 menu, 3, 1, do_menu,
 "sure you have prepared file by tftp, and press corresponding key",
 "sure you have prepared file by tftp \n"
 "press corresponding key, the u-boot will help you download file to the suited memory location \n"
 );
 得到：
 cmd_tbl_t __u_boot_cmd_menu Struct_Section = {"menu", 3, 1, do_menu, ...}
 
 #define Struct_Section  __attribute__((unused, section(".u_boot_cmd"), \
  aligned(4)))  //将这个结构体链接到.u_boot_cmd输入段

__attribute__： 需要了解一下gcc的__attribute__的编绎属性，__attribute__主要用于改变所声明或定义的函数或数据的特性
               它有很多子项，用于改变作用对象的特性
              
 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 * const []);
 char  *usage;  /* Usage message (short) */
#ifdef CONFIG_SYS_LONGHELP
 char  *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_s cmd_tbl_t

简单一点：
 struct cmd_tbl_s __u_boot_cmd_menu = {
                           .name = "menu",
                           .maxargs = 3,
                           .repeatable = 1,
                           .cmd = do_menu
 }
 
 从int (*cmd)(struct cmd_tbl_s *, int, int, char * const []); 看出do_menu应该有4个参数
 输入 menu 命令应该就会执行do_menu函数      

为u-boot添加menu菜单：

在common目录下添加这个程序：https://www.cnblogs.com/zhu-g5may/p/10084942.html

修改Makefile，编译进内核

效果：

CPUID: 32440001
FCLK:      400 MHz
HCLK:      100 MHz
PCLK:       50 MHz
DRAM:  64 MiB
WARNING: Caches not enabled
Flash: 0 KB
NAND:  256 MiB
In:    serial
Out:   serial
Err:   serial
Net:   dm9000
Hit any key to stop autoboot:  0
SMDK2440 #
SMDK2440 #
SMDK2440 #
SMDK2440 #
SMDK2440 # menu

##### u-boot cmd menu #####
[o] download u-boot to nor
[n] download u-boot to nand
[k] download kernel to nand
[f] download rootfs to nand
[b] boot the system
[q] quit from menu