Quartus® Prime Pro Edition User Guide: Power Analysis and Optimization

ID 683174
Date 4/01/2024
Document Table of Contents

1.3.4. Specifying Toggle Rates for Specific Nodes

You can assign toggle rates and static probabilities to individual nodes in the design. These assignments have the highest priority, overriding data from all other signal activity sources.

You must use the Assignment Editor or Tcl commands to create the Power Toggle Rate and Power Static Probability assignments. You can specify the power toggle rate as an absolute toggle rate in transitions per second using the Power Toggle Rate assignment, or you can use the Power Toggle Rate Percentage assignment to specify a toggle rate relative to the clock domain of the assigned node for a more specific assignment made in terms of hierarchy level.

Note: If you use the Power Toggle Rate Percentage assignment, and the node does not have a clock domain, the Quartus® Prime software issues a warning and ignores the assignment.

Assigning toggle rates and static probabilities to individual nodes is appropriate for signals in which you have knowledge of the signal being analyzed. For example, if you know that a 100 MHz data bus or memory output produces data that is essentially random (uncorrelated in time), you can directly enter a 0.5 static probability and a toggle rate of 50 million transitions per second.

The Power Analyzer treats bidirectional I/O pins differently. The combinational input port and the output pad for a pin share the same name. However, those ports might not share the same signal activities. For reading signal activity assignments, the Power Analyzer creates a distinct name <node_name~output> when configuring the bidirectional signal as an output and <node_name~result> when configuring the signal as an input. For example, if a design has a bidirectional pin named MYPIN, assignments for the combinational input use the name MYPIN~result, and the assignments for the output pad use the name MYPIN~output.

Note: When you create the logic assignment in the Assignment Editor, you cannot find the MYPIN~result and MYPIN~output node names in the Node Finder. Therefore, to create the logic assignment, you must manually enter the two differentiating node names to create the assignment for the input and output port of the bidirectional pin.