Scan-chain reordering
Beginner
Rearranging the chain of parts used for testing, so each link connects to a close neighbor instead of one far away.
Novice
For testing, a chip’s flip-flops (one-bit memories) are linked into long chains so a tester can load and read every bit. After placement, the order of flip-flops in each chain is changed so each link joins nearby flip-flops. The chip’s normal behavior does not depend on that order.
Expert
Driven by the DEF SCANCHAINS section: FLOATING lists may be reordered, ORDERED lists may not. Classically a traveling-salesman problem over flip-flop locations, constrained by chain partitions and clock domains. ATPG patterns must be regenerated for the new order.
Explained in Placement (Design Flow).