Intel® Quartus® Prime Software
Intel® Quartus® Prime Design Software, Design Entry, Synthesis, Simulation, Verification, Timing Analysis, System Design (Platform Designer, formerly Qsys)
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16012 Discussions

What exactly does Platform Designer do with unconnected component input ports?

New Contributor II

In RTL code one must tie input ports to ground or logic high if they are not being used. It is not possible to leave this upto to the synthesis tool.

If there are unconnected ports inside a platform designer system, we might get some warning. However, running Generate command will still complete without any fatal error. This is mind boggling.

What does platform designer do to unconnected ports when it runs through system generate and what happens to them when we run through complete compilation?

Is it a good idea to assign default input values at the port declaration of an entity to ensure that no strange behaviour takes place?

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3 Replies
Honored Contributor III

Are you talking about exported interfaces or interfaces that are simply not connected to other components in the system?

Exported interfaces are normally connected to something outside the system, like another part of your Quartus project or to I/O pins.  Interfaces that are not exported don't all have to be connected to something.  If they are unconnected, the unused logic is optimized away.  This happens in the HDL that is created from the system generation process.

I'm not sure why you think this is "mind boggling".  Synthesis does this whenever you compile a design whether you use Platform Designer or not.  The only difference is that the HDL code from the tool gets written this way as opposed to how the post-synthesis netlist is built (though the subsequent post-synthesis netlist will obviously also be missing this logic because it won't be in the HDL).

If you are referring specifically to an input, if for some reason the logic cannot be optimized away and the input value is required, you would most likely get a warning.


May I know whether the reply from sstrell answered your question? Do you need further help on this case?

Best Regards,
Richard Tan

p/s: If any answer from the community or Intel support are helpful, please feel free to give Kudos. 


I have yet to receive any response from you to the previous question/reply/answer provided but I believed that you have found a solution to this case. 
With that, I will now transition this thread to community support. If you have a new question, feel free to open a new thread to get the support from Intel experts. Otherwise, the community users will continue to help you on this thread. Thank you.

Best Regards,
Richard Tan

p/s: If any answer from the community or Intel support are helpful, please feel free to give Kudos.