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AR# 21223

7.1i XST - XST creates incorrect logic for signed multiplier

Description

Keywords: embedded, Virtex-4, Virtex-II

In my design, when the operands are used twice (once for unsigned and once for signed), XST creates one unsigned multiplier:

C <= A*B;
S <= tmp + signed(A)*signed(B);

XST only infers one multiplier for C and an adder for S. The logic inferred for S is incorrect.

Solution

This problem has been fixed in the latest 7.1i Service Pack available at:
http://www.xilinx.com/xlnx/xil_sw_updates_home.jsp
The first service pack containing the fix is 7.1i Service Pack 2.
AR# 21223
Date Created 09/04/2007
Last Updated 01/07/2009
Status Archive
Type General Article