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Observer
Observer
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Registered: ‎05-23-2014

cpri frame and synchronization interface behavior changed

Hello,

While upgrading our cpri design from Vivado 2017.2 to 2018.1, we observed a change in the behaviour of Xilinx cpri core Frame and synchronization interface.


-Vivado2017.2: it's possible to force iq_tx_enable signal timing by issuing a 260ns nodebfn_tx_strobe signal: xilinx cpri core aligns iq_tx_enable on last cpri_core_clock of nodebfn_tx_strobe pulse, and then following iq_tx_enables are issued every 260ns.
We really liked this behaviour because it let us control cpri frame start time not only at Basic Frame level, but also at single clock level (260 ns of uncertainty vs ~4ns of uncertainty on data propagation delays).

-Vivado2018.1: iq_tx_enable timing seems not to align to nodebfn_tx_strobe signal anymore: xilinx cpri core still tries to align iq_tx_enable by raising it on last cpri_core_clock of nodebfn_tx_strobe pulse, but the following iq_tx_enables are issued periodically with second-to-last iq_tx_enable phase (so now nodebfn_tx_strobe synchronizes cpri frame at Basic Frame level, but can't synch it at single clock level).


The aforementioned behaviours have been both simulated and hardware verified.
See screenshots below for visual explaination:

 

Vivado 2017.2 Behavior:
tx_strobe_2017.2.jpg

 

Vivado 2018.1 Behavior:

tx_strobe_2018.1.jpg

LogiCORE IP Product Guide ver 8.9 (PG056, page 62) is not clear on iq_tx_enable behaviour when a strobe not aligned with previous iq_tx_enables pulse is asserted, one thing for sure is that having iq_tx_enable adapt to nodebfn_strobe pulse made controlling cpri frame start time of our system way easier (also made possible to synchronize in time different CPRI cores sharing the same reference clock).


Questions:
- Is Vivado2018.1 Frame and Synch interface intended, or is it a bug? And if it is intended, why whas it changed?
- Can iq_tx_enable previous behaviour be restored on cpri core somehow?


Thank you.
Best Regards,

Giulio

 

 

 

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Moderator
Moderator
891 Views
Registered: ‎04-01-2018

 Hi Giulio,

 

We are working on this issue offline. Once the issue gets resolved we will update on this Post further.

 

With Best Regards,

Krishna Gadde 


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Moderator
Moderator
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Registered: ‎04-01-2018

This is a known issue in CPRI 8.9 in Vivado 2018.1. It will be fixed in Vivado 2018.3.

 

You can use the attached patch in AR (AR71369_Vivado_2018_1_preliminary_rev1.zip) to work around the problem.

 

Find the below link of the AR:

 

https://www.xilinx.com/support/answers/71369.html

 

 

With Best Regards,

Krishna Gadde

 

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Give Kudos to a post if it is helpful or gives an information.
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