9.4 Maximum Clock Frequency

Generally, you set clock constraints on clocks for which you have a specified requirement. The absence of violations indicates that this clock can run at least at the specified frequency. However, in the absence of such requirements, you may still be interested in computing the maximum frequency of a specific clock domain.

To obtain the maximum clock frequency, a static timing analysis tool computes the minimum period for each path between two sequential elements. To compute the maximum period, the tool evaluates the maximum data path delay and the minimum skew between the two elements, as well as the setup on the receiving sequential element. It also considers the polarity of each sequential element. The maximum frequency is the inverse of the largest value among the maximum period of all the paths in the clock domain. The path responsible for limiting the frequency of a given clock is called the “critical path.”