FIFO是通过时钟来确定是同步还是异步的，同步FIFO的读写操作是通用一个时钟来控制的。另一方面。两个不同频率或者不同香味的时钟来控制异步FIFO的读写操作。

异步FIFO 跨越时钟域的同步问题-FIFO is determined by the clock is synchronous or asynchronous, synchronous FIFO read and write operations are a common clock control. on the other hand. Two different frequencies or different flavor to control the clock asynchronous FIFO read and write operations. FIFO　asynchronous clock domain crossing synchronization issues