LNT-30026: LUT With More Than 1 Input Driving Primary Device Output Ports

Description

Violations of this rule identify lookup tables that combine more than one input signal and drive into primary device output ports. Any time a lookup table has multiple inputs, there is a risk of signal transitions arriving at those inputs at different times and creating glitches at the LUT output. These relative delays may differ between compiles as the optimization solution changes.

Without careful consideration and timing constraints, glitches on primary device output ports can trigger spurious and unexpected off-chip events.

Recommendation

If the violating LUT cannot be removed or its output cannot be registered, ensure that it is properly timing constrained to avoid glitches and waive its violation.

Severity

Low

Tags

Tag Description
nonstandard-timing Design rule checks related to topologies which have unique timing analysis methodologies and may prove problematic.

Device Family

  • Intel Agilex®
  • Intel Agilex®
  • Intel Agilex®
  • Intel®Stratix® 10
  • Intel®Arria® 10
  • Intel®Cyclone® 10 GX