void goto_shell(const char *str)
{
    printf("%s \r\n", str);
    start_shell();
}

void goto_boot_from_app(void)
void update_from_backup(int size);

void main()
{
    boot_cnt++;
    
    if (boot_cnt >= (3 + 2))
        goto_shell("Exceeded the maximum number of boot count.");
    
    if (app_has_data && (!update_flag) && (boot_cnt <= 3))
        goto_boot_from_app(Boot APP normally ...);
    
    if (!backup_has_data)
        goto_shell("Backup has no data.");

    if (backup_crc_store != backup_crc_cal)
        goto_shell("Backup crc error.");
    
    if (app_crc_store == backup_crc_store)
        goto_boot_from_app(APP and backup are same, so we do not uodate. Boot APP ...);
    
    update_cnt++;
    rt = update_from_backup(backup_size);
    if (rt != SUCCESS)
        reset();
    
    goto_boot_from_app(Upate APP from backup success. Boot APP ...);
}