说明：  用FPGA实现大型设计时，可能需要FPGA具有以多个时钟运行的多重数据通路，这种多时钟FPGA设计必须特别小心，需要注意最大时钟速率、抖动、最大时钟数、异步时钟设计和时钟/数据关系。设计过程中最重要的一步是确定要用多少个不同的时钟，以及如何进行布线
(Realize large-scale use of FPGA design, may need to FPGA with multiple clocks to run multiple data path, the multi-clock FPGA design must be particularly careful to note the maximum clock rate, jitter, the largest number of clock, asynchronous clock design and clock/data relations. The design process the most important step is to determine how much it costs to different clocks, as well as how to carry out wiring)