Xilinx Answer #668 : FITNET/FITEQN: packing more pterms into an FFB macrocell

Answers Database

FITNET/FITEQN: packing more pterms into an FFB macrocell

Record #668
Problem Title:
FITNET/FITEQN: packing more pterms into an FFB macrocell

Problem Description:

Solution 1:

PROGRAM: FITEQN, FITNET

VERSION: 5.0, 5.1

PLATFORM: All

SHORT DESCRIPTION:

A way to pack more pterms into a Fast Function Block macrocell

LONG DESCRIPTION:

PROBLEM:

Currently the fitter used in 5.0 and 5.1 allows a default of 4 product terms
maximum in an FFB output. This causes the fitter to break up large equations
into multiple macrocells.

This results in two problems:

1) It slows the design down.

2) It can waste resources. This happens if the equation is later DeMorganed
    to use fewer than 4 pterms. In this case, the software could have fit the
    equation into a single macrocell instead of splitting it.

SOLUTION:

Copy the file XACT\DATA\XEPLD.CFG into the project directory. Edit the last
line:

    alias ffb_pterm_limit 36

so that it is surrounded by parentheses:

   (alias ffb_pterm_limit 36)

This will change the maximum to 36 pterms.

Note: The 5.2 software will automatically default to 36.

End of Record #668 - Last Modified: 11/06/96 03:41

For the latest news, design tips, and patch information on the Xilinx design environment, check out the Technical Tips!