当一个设备驱动需要处理它的硬件的反应时间, 涉及到的延时常常是最多几个毫秒. 在这 个情况下, 依靠时钟嘀哒显然不对路. The kernel functions ndelay, udelay, and mdelay serve well for short delays, delaying execution for the specified number of nanoseconds, microseconds, or milliseconds respectively.* Their p