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alexis_jp
Explorer
Explorer
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Registered: ‎09-10-2019

GTWizard Dynamic Frac-N and COMMON in the example design?

I can't successfully generate the COMMON logic for my needs.

I want to use both QPLL0 and QPLL1 using the Dynamic Frac-N/SDM feature.

The sdm* signals are hard coded and aren't exposed in the common wrapper.

Also, QPLL0_SDM_CFG0 and QPLL1_SDM_CFG0 stay at 0... the bit7 should be 1.

The sdm signals are greyed out and can't be exposed from the wizard.

 

How to enable Dynamic Frac-N in the wizard with GTCOMMON in the example design?

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roym
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Registered: ‎07-30-2007

On the structural options tab if you put the GT*_COMMON in the core you can choose to bring the SDM* IO's to the top level.  If you choose to put the GT*_COMMON in the example design you can't bring them to the top level as they are already in the example design where you can work with them, however, you may have to do some coding to bring them to the top level.  So if the common is in the example design the choice to bring them to the top level is greyed out.  If you have no other reason to put the GT*_COMMON in the example design then leave it in the core and let the wizard do the wiring for you.




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alexis_jp
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Registered: ‎09-10-2019

@roymWe need the GT*_COMMON in the example design to be able to use both QPLLs at the same time and having something more scalable and usable than the gtwizard.

As said, the problem comes from QPLL0/1_SDM_CFG0 that is defined as Reserved in the UG.

I know from a different source that the generated value of QPLL0_SDM_CFG0 is wrong, the bit 7 should be high when the frac-N feature is used but it's not.

Since it's defined as Reserved in the UG and the GTWizard generates a wrong value, I don't want to overwrite that undocumented value.

That is the reason of my question, Frac-N/SDM feature + GT*_COMMON outside of the core => How?

Any information on that?

 

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roym
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Registered: ‎07-30-2007

Is it possible that your wizard design isn't enabling FRAC-N to begin with?  If not I would say it is a good idea to enable it there so you are not missing any other settings.   When you put the common outside the core it is in the design at a lower level of hierarchy but accessible to you so you could make settings changes.  See attached.  I notice that the *_cfg0 is an attribute and not a port so you would have to change that setting through the GT_COMMON's DRP ports.

To enable fracn press the calc button in the wizard.  If it is enabled there will be a fractional part number as shown below.




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gtcommon.JPG
fracn.JPG
alexis_jp
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Registered: ‎09-10-2019

@roymOf course Frac-N is already enabled. I could confirm it with the SDM0/1DATA. It contains the frac value defined in the gtwizard.

I don't see how the DRP has something to do with that parameter. It's defined in the code when the common is in the core.

That's an undocumented parameter then I need the gtwizard to generate the value correctly.

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roym
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Registered: ‎07-30-2007

If you have a Wizard design that where Frac-N is enabled but not working then please attach the *.XCI file here and we will investigate.




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