More "timing closure efficient" Timing Driven Placements by implementing
our new net weight for negative slack paths to enhance timing closure
behavior is provided by a NSRF (Negative Slack Recover Factor). This new
weight would not be based on the absolute amount of negative slack in a
path, but rather it would be based on the proportion or percentage of the
path's total net delay adder that must be recovered in order to achieve
timing closure (zero slack). After an initial or previous placement has
been created, then a list of paths with timing violations with a Negative
Slack Recover Factor (NSRF) is created for each net in each of the timing
paths on the list of paths, and then calculating a NSRF net weight factor
for use in subsequent placements and also assigning nets in the list of
paths with no timing violations a NSRF default value of one. The NSRF
value is calculated as equaling (ZWLM slack value+negative slack
value)/ZWLM slack value=(1+(negative slack value/ZWLM slack value)),
where ZWLM is a Zero Wire Load Model (ZWLM) value of timing wherein all
wire parasitics are removed from consideration in the timing.