11.4.5 CLKINT/CLKBUF for Reset and/or High Fanout Networks

Many designs have internally generated clocks, high fanout control signals, or internally generated reset signals. These signals need a large internal driver, CLKINT, to meet both area and performance goals for the circuit. If the high fanout signals come directly into the design through an I/O, a CLKBUF driver is used. Most synthesis tools do not automatically use these drivers. Instead, the synthesis tool builds a buffer tree that consumes one module per driver. On a high fanout net this can affect both the area and timing for that signal. If the global drivers for a given array are still available, you should instantiate the CLKINT or CLKBUF driver into the design. The following example shows how to instantiate these drivers.