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AR# 18924

7.1i CPLDFit XC9500 CoolRunner/-II - "WARNING:Cpld:179 - The signal(s) '%s' are in combinational feedback loops"


General Description:

When my design contains a combinational feedback loop, a message similar to the following occurs:

"WARNING:Cpld:179 - The signal(s) 'test' are in combinational feedback loops.

These signals may cause hazards/glitches. Logic should include hazard reduction circuitry to avoid hazards/glitches. Apply the NOREDUCE parameter to the hazard reduction circuitry."


This warning message reminds you to check for glitches or hazards. Hazard reduction circuitry is redundant in logic optimization. To prevent the CPLD Fitter from optimizing this redundant logic away, add a NOREDUCE attribute to the equation to instruct the CPLD Fitter to not optimize this equation.

For more details on applying the NOREDUCE attribute, see the "Constraints Guide", which can be accessed at:


AR# 18924
Date 12/15/2012
Status Active
Type General Article