8.2 Logical Cones

A logical cone is a window that displays only a portion of the netlist. You create this window in a Netlist Viewer and simply select the objects that you want to appear in the separate view. You can add individual instances, blocks, nets, and ports to a logical cone. You can also remove design objects from this cone. Logical cones are useful for debugging and path analysis, especially for timing-critical nets.

Logical cones help you navigate and analyze a specific part of the design in which you are interested. A logical cone view is very similar to the Netlist Viewer view. The main differences between the Logical cone and Netlist Viewer views are:

• In a logical cone, you see only the pieces of the design you want to focus on (for example, analysis of timing-critical paths) whereas in Netlist Viewer, you see the entire netlist.
• In a logical cone, a net appears as a dashed line rather than a solid line unless all instances that are connected to that net are also present in the Logical Cone view. These dash-line nets are designated as partially connected, as opposed to fully connected nets (solid lines).
• In a logical cone, all objects of the netlist appear on a single sheet, with hierarchical boundaries still visible. This is a trade-off between the classical hierarchical view, where you must use Push and Pop commands to navigate in the netlist, and the flattened view, where hierarchy is simply ignored.