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AR# 20354

6.3i XST- XST incorrectly synthesizes a mux driving a comparator

Description

Keywords: decoder, if, case

Using the code below, for a mux driving a comparator, XST removes too many signals from the mux:

Match_count <= "11001" when sel = '1' else "11011";

q<='1' when (in1(4 downto 0) >= Match_count) else '0';

Solution

This issue is fixed in ISE 7.1i

To work around this in the 6.3i software, replace the line:

Match_count <= "11001" when sel = '1' else "11011";

with the line:

Match_count <= "110"&(not cmpsel)&'1';
AR# 20354
Date Created 11/10/2004
Last Updated 07/02/2007
Status Archive
Type General Article