Scan Chain Reordering

Scan chain reordering is a process which is done in the Physical Design to optimize the congestion while doing placement. When we do Scan Stitching , we don't have any information of where the Flip-Flop will be placed physically. So it is possible to have registers which are placed far from each other but getting stitched in the same scan chain. Also they may not be having any valid paths between them functionally.Hence the Physical Design tool has to route between these two far away Flip-Flop just for scan purpose. But with scan reordering , the Physical Design tool reorders the registers in the scan chains based on the placement if them to reduce the scan wire length.