ALTDDIO_IN Seems Slow

[GLees]

I'm designing a deserializer in Cyclone V and see something strange with a simple ALTDDIO_IN megafunction;

If I leave the clock and data_in ports unassigned the timing analyzer states an Fmax of around 400Mhz which matches up with the datasheet.  As soon as I assign physical LVDS pins to the ports the Fmax drops to around 200Mhz.  What gives?

[Nurina]

Hello,

So you've assigned the pin?

Is it possible that you've seen the Critical Warning mentioned in this KDB: https://www.intel.com/content/www/us/en/support/programmable/articles/000076713.html

May I know which Quartus version you're using?

Thanks,

Nurina

[GLees]

Yes, I've assigned physical pins, valid LVDS clock and LVDS input.  I see no critical warnings.  I'm using version 18.1.0.

Thanks for you response,

Greg

[Nurina]

Hello,

Can you share your design so I can investigate this further?

Regards,

Nurina

[GLees]

I show the design in my original post.  I'm not sure what more you need.

[Nurina]

Hi,

Please share the .qar file. To generate this, go to Project>Archive Project.

So that I can see what other settings you have applied in the project.

Regards,

Nurina

[GLees]

I started to prepare a .qar file by recompiling the project and then ran the timing analyzer one last time.  Lo and behold I now get an Fmax around 400Mhz like it should be.  I don't know how to explain this.  I guess for now the problem is solved.

[Nurina]

Hello,

That is odd, but since the problem has been solved I shall close this case. If you have a new question, please login to https://supporttickets.intel.com , view details of the desire request, and post a feed/response within the next 15 days to allow me to continue to support you. After 15 days, this thread will be transitioned to community support. The community users will be able to help you on your follow-up questions.

p/s: If any answer from community or Intel support are helpful, please feel free to mark as solution, give Kudos and rate 4/5 survey

Regards,

Nurina