Ambit BuildGates Synthesis User Guide

Setting Constraints

Wire Load Model Selection

Figure 6-19 provides a flow chart of the algorithm used for selecting a wire load model for a net.

Figure 6-19 Finding Wire Load Model W for a Net N

Net N

Find module modx that encloses net N

Find hierarchically lowest level module M enclosing modx with user specified wire load model W

Wireload mode = enclosed

Lookup wire load model W from module

Wire Load Model W

Ambit BuildGates Synthesis User Guide

Setting Constraints

Figure 6-20 depicts the wireload for a net, where T is the current top module, A is an instance inside T, and M1 and M2 are two instances inside A. The net net1 is fully contained inside A, but not fully contained inside either M1 or M2.

Figure 6-20 Estimating the Wireload for a Net

T

A

M1 M2

net1

top

enclosed

The wire load for net1 is estimated as follows:

■Identify the enclosing module for net1. In the figure above, module A is the enclosing module.

■For A or its parent modules (modules in its upward hierarchical path), identify if wire load table is already set.

■If set, use it as the wire load table.

■If not set, check the global wire load mode (by default, this is top).

■If the mode is enclosed, use the area of enclosing module A to identify the wire load table.

■If the mode is top, use the area of top module T to identify the wire load table.

The area look-up table for the wire load model is in the technology file.