As anyone who's routed a pc board knows, a successful routing job combines intuition, speed, and good old-fashioned design chops. EDA vendors and pc-board-tool homebrewers alike have sought to build all of the above into automatic routing tools. But an algorithm that mimics the pattern-recognition capabilities of a good, experienced manual routing job has proved elusive.
In its new topology-routing technology, Mentor Graphics may have come the closest to date to enabling an autorouter to foster close collaboration between the design engineer, who oversees the system design, and the board designer, who translates the system requirements into a layout. Intended as an optional add-on to Mentor's existing Board Station and Expedition PCB design flows, the topology router consists of two applications.
The first is a topology planner used by design engineers to sketch out the placement of major components in their design. Traditionally, this stage of the board placement is done on paper to give the board designer guidance. But the topology planner goes much further, allowing the designer to plan and optimize the buses and subsystem interconnects on the pc board (see the figure). It broadens the component-placement routine to encompass the performance of the logic pathways between those components.
The second application is the topology router itself, which automatically routes the bus interconnects while following the pathways defined by the designer. In so doing, it creates a routing structure that mimics the results that experienced board designers can create by hand.
Moreover, it does so while avoiding the labyrinth of iterations that would ordinarily take place between the circuit designer and board designer to fine-tune the device placement. Additionally, the router facilitates a layout that meets the delay criteria and other constraints for the signal paths.
The design and structure of the bus paths is stored with the design database, enabling incremental modifications of the board or future reuse of the bus structures without re-routing.
The topology-router technology will be available in the fourth quarter as an option to both the Expedition Enterprise and Board Station PCB design flows.