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jsmithsrc
Adventurer
Adventurer
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Registered: ‎06-25-2012

UltraScale clocking wizard safe clock startup timing failure

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I am seeing a timing failure due to Safe Clock Startup feature in Clocking Wizard, as described in PG065 v6.0 pg 71. I am using Vivado 2017.4.

The suggested solution is to insert another BUFGCE on output of MMCM in parallel with the BUFGCE that feeds the shift registers to enable safe clock startup.

My question is: If I am using the Clocking Wizard IP, how do I get direct access to the MMCM clock output to place this clock buffer manually? I only have access to the generated clocks and the locked signal.

I'm going to assume I would need to manually edit generated Clocking Wizard IP or construct my own HDL design with the same effect?

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jsmithsrc
Adventurer
Adventurer
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Registered: ‎06-25-2012

You understand my question.

Unfortunately, when Safe Clock Startup is selected on "Clocking Options" tab, the only available option in the "Drives" column if BUFGCE.  If Safe Clock Startup is not selected, then I agree with your assessment. So it seems my only choice here would be to use unbuffered outputs and implement the safe clock startup function myself.

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evant_nq
Explorer
Explorer
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Registered: ‎07-18-2018

hi jsmithsrc,

    If your goal is to do something like this from the PG:

 

GOAL.PNG

With using the Wizard, I think you likely will just need to turn off the output buffer for the clock. If you go to the output clocks page you can see the Drivers. If you select none you will just get the MMCM port output, not the buffer output. Then just add all your BUFGs after the MMCM instance as needed:

 

GOAL2.PNG

jsmithsrc
Adventurer
Adventurer
956 Views
Registered: ‎06-25-2012

You understand my question.

Unfortunately, when Safe Clock Startup is selected on "Clocking Options" tab, the only available option in the "Drives" column if BUFGCE.  If Safe Clock Startup is not selected, then I agree with your assessment. So it seems my only choice here would be to use unbuffered outputs and implement the safe clock startup function myself.

View solution in original post

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