4.11.1. Design Recommendations
In a synchronous design, a clock signal triggers all events. When you meet all register timing requirements, a synchronous design behaves in a predictable and reliable manner for all process, voltage, and temperature (PVT) conditions. You can easily target synchronous designs to different device families or speed grades.
Clock signals have a large effect on the timing accuracy, performance, and reliability of your design. Problems with clock signals can cause functional and timing problems in your design. Use dedicated clock pins and clock routing for best results, and if you have PLLs in your target device, use the PLLs for clock inversion, multiplication, and division. For clock multiplexing and gating, use the dedicated clock control block or PLL clock switchover feature instead of combinational logic, if these features are available in your device. If you must use internally-generated clock signals, register the output of any combinational logic used as a clock signal to reduce glitches.
Consider the architecture of the device you choose so that you can use specific features in your design. For example, the control signals should use the dedicated control signals in the device architecture. Sometimes, you might need to limit the number of different control signals used in your design to achieve the best results.