arm9_uboot add commands

Serial data is received and passed to run_command () function, run_command () function call common / command.c implemented find_cmd () function to find the u_boot_list command section, and returns cmd_tbl_t structure. Then run_command () function returns a pointer cmd_tbl_t structure used in the function call do_hello (), thereby completing execution of the command

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 */
}

In u-boot.1.1.6 / board / 100ask24x0 / u-boot.lds in

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

In u-boot.1.1.6 / include / command.h in

#define U_BOOT_CMD(name,maxargs,rep,cmd,usage,help) \
cmd_tbl_t __u_boot_cmd_##name Struct_Section = {#name, maxargs, rep, cmd, usage}

Struct_Section the __attribute__ #define ((unused, sectionTop ( ".u_boot_cmd"))) 
// can be interpreted as: instantiating a cmd_tbl_t type structure, and save it in the section where .u_boot_cmd

In u-boot.1.1.6 / include / command.h, the following definitions cmd_tbl_t

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;

In u-boot.1.1.6 / common, the new file cmd_hello.c

#include <common.h>
#include <command.h>

int do_hello ( cmd_tbl_t *cmdtp, int flag, int argc, char *argv[] )
{
    printf("this is hello!\n");
    return 0;
}

U_BOOT_CMD(
    hello, 1, 0, do_hello,
    "hello\t- this cmd is hello\n",
    "this cmd is hello,too\n"
);

After addition cmd_hello.o behind u-boot.1.1.6 / common / Makefile of COBJS; in the root directory make, programming; hello new commands can occur