为什么打印函数rt_kprintf("");会多一个空行？

请问达人们，为什么打印出来的行与行之间会多一行? 突然中间就多一行，图2

代码如下，是例程。

谢谢

static void led2_thread_entry(void parameter)
{
rt_pin_mode(LED2_PIN, PIN_MODE_OUTPUT);
while (1)
{
//rt_pin_write(LED2_PIN, PIN_LOW);
rt_kprintf("led off\n");
rt_kprintf("led off\n");
rt_kprintf("led off\n");
rt_kprintf("led off\n");
rt_kprintf("led off\n");
// rt_kprintf("led off\n");
// rt_kprintf("led off\n");
// rt_kprintf("led off\n");
// rt_kprintf("led off\n");
// rt_kprintf("led off\n");
rt_thread_delay(1000); / 延时300个tick /
// rt_pin_write(LED2_PIN, PIN_HIGH);
// rt_thread_delay(1000); / 延时300个tick */
}
}