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AR# 18397

XST - "WARNING:Xst:1293 - FF/Latch <my_flop> is constant in block <my_block>"

Description

Keywords: INIT, synthesize, optimization

When I synthesize a design with XST, the following warning occurs:

"WARNING:Xst:1293 - FF/Latch <my_flop> is constant in block <my_block>."

Solution

This warning occurs when a register with an INIT value has a constant input that matches the INIT value and no other control signal (such as a local set/reset). The constant input might be due to an undriven input or logic optimization.

To avoid the warning, examine the logic value and/or trimming at the input signal of the register to be sure no unexpected optimization has been done.
AR# 18397
Date Created 09/03/2007
Last Updated 01/08/2009
Status Active
Type General Article