HOME       UP       PREV       NEXT (Power Estimation Formula)  

Rent's Rule Estimate of Wire Length

If we know the physical area of each leaf cell we can estimate the area of each component in a heirarchic design (sum of parts plus percentage swell).

Rent's rule pertains to the organization of computing logic, specifically the relationship between the number of external signal connections to a logic block with the number of logic gates in the logic block, and has been applied to circuits ranging from small digital circuits to mainframe computers »[Wikipedia].

Rent gives a simple power-law relationship and wire length distribution (with good placement) follows an equally-predictable pattern.

With a heirarchic design, where we have the area use of each leaf cell, even without placement, we can follow a net's trajectorary up and down the hierarchy and apply Rent's Rule.

Hence we can estimate a signal's length by sampling a power law distribution whose 'maximum' is the square root of the area of the lowest-common-parent component in the hierarchy.

10: (C) 2008-13, DJ Greaves, University of Cambridge, Computer Laboratory.