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rodrigomelo9
Observer
Observer
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Registered: ‎05-07-2021

MMCME4 with ZHOLD does not drive sequential IO

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Hi. I generated an MMCM4_ADV instantiation with the Clock Wizard (targeting a ZU9EG device), where the COMPENSATION parameter is assigned with "AUTO".

According to UG572:

3. The COMPENSATION attribute values are documented for informational purpose only. The Vivado tools automatically select the appropriate compensation based on circuit topology. Do not manually select a compensation value, leave the attribute at the default value.

 

But elaborating the design (synth_design -rtl -rtl_skip_mlo) and running report_methodology:

CLKC-22#1 Advisory
MMCME4 with ZHOLD does not drive sequential IO
The MMCME4 cell clocks/mmcm/mmcme4_adv_inst has COMPENSATION value ZHOLD, but CLKOUT0 output does not drive any sequential IO cells. It is recommended to use the MMCM without a feedback buffer and set COMPENSATION to INTERNAL.
Related violations: <none>

 

Is safe to ignore it? Can I solve this issue?

Regards,

Rodrigo

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dsheils
Moderator
Moderator
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Registered: ‎01-05-2017

HI @rodrigomelo9 

The message here shown by Vivado is really just an advisory or recommended good practice. 

ZHOLD: Indicates the MMCM is configured to provide a negative hold time at the I/O registers but your MMCM is not driving any sequential IO cells so you should be ok to let the tool decide what mode to use.

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dsheils
Moderator
Moderator
256 Views
Registered: ‎01-05-2017

HI @rodrigomelo9 

The message here shown by Vivado is really just an advisory or recommended good practice. 

ZHOLD: Indicates the MMCM is configured to provide a negative hold time at the I/O registers but your MMCM is not driving any sequential IO cells so you should be ok to let the tool decide what mode to use.

-------------------------------------------------------------------------
Don’t forget to reply, kudo, and accept as solution.
-------------------------------------------------------------------------

View solution in original post

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