When I run the implementation process, a message similar to the following occurs:
"WARNING:Cpld:1007 - Removing unused input(s) 'DATAIN'. The input(s) are unused after optimization. Please verify functionality via simulation."
This message occurs because your design has unnecessary inputs for one of the following reasons:
- An input is declared but never used in your design.
- A logic error in your design changes an input to a "don't care" input.
- Unconnected logic or an unconnected output results in logic trimming back to the input.
If you recognize that the input falls into one of the above three situations, but still do not want the input to be trimmed, select the "Preserve Unused Inputs" option in "Fit Process Properties" under the Advanced options section.
- 6.x: Advanced options need to be enabled from ISE using the Edit->Preferences->Processes->Advanced pull-down menu.
- 7.x: Advanced options need to be enabled from ISE by changing the 'Property Display Level' in the Fit process properties box.
This option prevents the pin from being connected to any logic in the device, and warning messages are not produced for unused inputs. The input will appear in the Fitter report, but will NOT be locked to the desired pin.
To work around this issue, Xilinx recommends creating a dummy output and connecting the input to the output in your design. This solution prevents the tools from trimming the input pin, and the input will be locked to the desired pin. If a number of inputs are trimmed, you can simply create any combinatorial logic function using the inputs in question and route it to the dummy output pin. When the design is complete, the dummy output can be removed from your design.