让uboot按下指定键停止autoboot

默认uboot是按下任意键停止autoboot，有人觉得不爽，害怕终端操作用户误操作，要指定特殊按键
这个功能很简单，例如要按下ESC键，停止自动boot
只需要添加

#define CONFIG_AUTOBOOT_KEYED 1
#define CONFIG_AUTOBOOT_PROMPT "Press ESC to abort autoboot in %d seconds"
#define CONFIG_AUTOBOOT_DELAY_STR "linux"
#define CONFIG_AUTOBOOT_STOP_STR "\x1b"

即可，0x1B就是ESC的ascii码

在2008.10等高版本uboot上这样做就可以了，低版本的倒计时有些问题，以下是我在uboot1.3.4上的修改

#if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0)
# if defined(CONFIG_AUTOBOOT_KEYED)
static __inline__ int abortboot(int bootdelay)
{
    int abort = 0;
    unsigned int start_tick = get_ticks();
    uint64_t t1=endtick(1);

    uint64_t etime = endtick(bootdelay);
    struct {
        char* str;
        u_int len;
        int retry;
    }
    delaykey [] = {
        { str: getenv ("bootdelaykey"),  retry: 1 },
        { str: getenv ("bootdelaykey2"), retry: 1 },
        { str: getenv ("bootstopkey"),   retry: 0 },
        { str: getenv ("bootstopkey2"),  retry: 0 },
    };

    char presskey [MAX_DELAY_STOP_STR];
    u_int presskey_len = 0;
    u_int presskey_max = 0;
    u_int i;

#  ifdef CONFIG_AUTOBOOT_PROMPT
    printf(CONFIG_AUTOBOOT_PROMPT,bootdelay);
    printf("\b\b\b\b\b\b\b\b\b");
#  endif

#  ifdef CONFIG_AUTOBOOT_DELAY_STR
    if (delaykey[0].str == NULL)
        delaykey[0].str = CONFIG_AUTOBOOT_DELAY_STR;
#  endif
#  ifdef CONFIG_AUTOBOOT_DELAY_STR2
    if (delaykey[1].str == NULL)
        delaykey[1].str = CONFIG_AUTOBOOT_DELAY_STR2;
#  endif
#  ifdef CONFIG_AUTOBOOT_STOP_STR
    if (delaykey[2].str == NULL)
        delaykey[2].str = CONFIG_AUTOBOOT_STOP_STR;
#  endif
#  ifdef CONFIG_AUTOBOOT_STOP_STR2
    if (delaykey[3].str == NULL)
        delaykey[3].str = CONFIG_AUTOBOOT_STOP_STR2;
#  endif

    for (i = 0; i < sizeof(delaykey) / sizeof(delaykey[0]); i ++) {
        delaykey[i].len = delaykey[i].str == NULL ?
                    0 : strlen (delaykey[i].str);
        delaykey[i].len = delaykey[i].len > MAX_DELAY_STOP_STR ?
                    MAX_DELAY_STOP_STR : delaykey[i].len;

        presskey_max = presskey_max > delaykey[i].len ?
                    presskey_max : delaykey[i].len;

#  if DEBUG_BOOTKEYS
        printf("%s key:<%s>\n",
               delaykey[i].retry ? "delay" : "stop",
               delaykey[i].str ? delaykey[i].str : "NULL");
#  endif
    }

    /* In order to keep up with incoming data, check timeout only
     * when catch up.
     */

    while (!abort && get_ticks() <= etime) {
        for (i = 0; i < sizeof(delaykey) / sizeof(delaykey[0]); i ++) {
            if (delaykey[i].len > 0 &&
                presskey_len >= delaykey[i].len &&
                memcmp (presskey + presskey_len - delaykey[i].len,
                    delaykey[i].str,
                    delaykey[i].len) == 0) {
#  if DEBUG_BOOTKEYS
                printf("got %skey\n",
                       delaykey[i].retry ? "delay" : "stop");
#  endif

#  ifdef CONFIG_BOOT_RETRY_TIME
                /* don't retry auto boot */
                if (! delaykey[i].retry)
                    retry_time = -1;
#  endif
                abort = 1;
                printf("\n");
            }
        }

        if(get_ticks() > t1)
        {
            bootdelay--;
            printf("%d\b",bootdelay);

               t1=endtick(1);
        }

        if (tstc()) {
            if (presskey_len < presskey_max) {

                presskey [presskey_len ++] = getc();
            }
            else {
                for (i = 0; i < presskey_max - 1; i ++)
                    presskey [i] = presskey [i + 1];

                presskey [i] = getc();
            }
        }
    }
#  if DEBUG_BOOTKEYS
    if (!abort)
        puts("key timeout\n");
#  endif

#ifdef CONFIG_SILENT_CONSOLE
    if (abort)
        gd->flags &= ~GD_FLG_SILENT;
#endif

    return abort;
}

# else    /* !defined(CONFIG_AUTOBOOT_KEYED) */