Advanced Maneuvers in Feedthrough Insertion: Maximizing Routability while Minimizing Port Creation

Previously I wrote about the basics of feedthrough insertion in Encounter.  Today I'd like to push into a tiny but powerful example of how Encounter's feedthrough insertion solution can derive solutions that enable rapid top-level design closure.

Feedthrough insertion in Encounter has two modes of operation: Placement-based -or- route-based.  The advantage of route-based is its awareness of congested vs. sparse areas of the design.  Encounter's high capacity virtual flat view of the design combined with hierarchically aware track-assignment-based trial routing provides design insight not usually available until after partitioning and reassembly.  We can use this information to derive feedthrough insertion and pin assignment with a high degree of routability.

Once we embark up on deriving feedthrough insertion solutions based on trial routing, some interesting situations arise.  Take for example the one pictured below.  The design has 4 partitions.  The example net potentially in need of feedthrough insertion is driven from an instance within the partition on the lower left to a partition on the upper right.  I've highlighted the net showing how it crosses over the neighboring partition to the lower right:

If we run route-based feedthrough insertion it will follow the topology of the net, determine which partitions it crosses, and insert feedthroughs generally along the route.

Here is the command:
insertPtnFeedthrough -chanLess -doubleBuffer -routeBased

And here is the result:

After performing pin assignment (assignPtnPin) and commiting the partitions (partition) the result is neatly aligned connections on the partitions with no top level routing crossing over partitions:

This solution is fine, but what if we wanted to reduce the number of ports created and feedthrough buffers inserted?  For this particular net we could avoid the need for feedthrough buffers all together if we instead assign the partition pins for the lower left and upper right partition along the common edge they share in the center of the design.

But how can derive the benefits of route-based feedthrough insertion while still detecting situations where it would be better to instead simply align pins on common edges in situations like this?  There's a very useful switch called "-preferPinAbutment" that will give us the best of both worlds.  With it, the tool will perform route-based feedthrough insertion and back off in situations where a common edge is available -- unless the common edges are highly congested.

insertPtnFeedthrough -chanLess -doubleBuffer -routeBased -preferPinAbutment

I remember working with our developers on this capability years ago.  I thought it was a stretch when I asked them for it but I was pleased when they implemented it.  There are a number of other capabilities insertPtnFeedthrough has that are subtly powerful.  I'll be talking about them in future blog posts.

Have you used Encounter's feedthrough insertion functionality?  If so I'd love to hear what's working and what's not in the comments.

Bob Dwyer