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AR# 20089

LogiCORE Adder/Subtractor v6.0 - NGDBuild issues warning: "WARNING:NgdBuild:452 - logical net 'Q_C_OUT' has no driver" and MAP issues error: "ERROR:MapLib:661"

Description


When I use the Adder/Subtracter Core v6.0 provided with COREGen, the following warning occurs in NGDBuild and the following error occurs in MAP:

"WARNING:NgdBuild:452 - logical net 'sum_of1p' has no driver"
"ERROR:MapLib:661 - LUT3_L symbol "clip8_01_U1__n0000<0>1" (outputsignal=clip8_01_U1__n0000<0>1/O) has input signal "sum_of1p" which will betrimmed. See the trim report for details about why the input signal willbecome undriven."

Solution


This error and warning message might be caused by the Adder/Subtracter Core v6.0. An incorrect setting for the carry and overflow options regarding the output size/type cause these messages.
Refer to the Core Data Sheet table "Availability of Carry/Borrow/Overflow Outputs and Output Data Type/Size Against Input Data Type" in the latest documentation found at:
http://www.xilinx.com/support/documentation/ipmath_addersubtractor_adder-subtractor.htm
This is not an issue in Core version 7.0 since the CORE Generator software does not allow the conflicting setting.
However, if the Core is upgraded from version 6.0 to 7.0, you must regenerate the v7.0 Core from scratch. The CORE Generator GUI feature "File -> Execute Command File" allows you to select the XCO file generated from v6.0, but do not use the v6.0 XCO file. Instead, generate the v7.0 Core from scratch.
AR# 20089
Date Created 09/03/2007
Last Updated 12/15/2012
Status Active
Type General Article