Scan Chain Reordering

We know how scan chains are being inserted and how it effects the circuit. Now let’s focus on the main topic that is, how tool optimizes the scan chain.
Reordering of the scan chain helps in optimizing the routing resources and make design decongested. This is known as scan chain reordering. Lets take one example of before and after scan chains and see how the routing resources are being saved.

Before Scan Chain Reordering:

before-scan-chain-reordering -vlsi
Before Scan Chain Reordering

In the above figure, we can see that route1 and route2 completes the scan chain routing which is comparatively longer route than after scan chain reordering where we have small route length completing our requirement. During placement optimization, tool does these optimizations to save route tracks for the clock/signal routing at later stages.

After the Scan Chain Reordering:

After the Scan Chain Reordering

We have less routing congestion and is getting estimated by trial route run.


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