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Participant s1gandhi
Participant
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Registered: ‎06-24-2019

GTY serdes QPLL1 for 14.6456 G

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capture.PNG

 

I want to understand why for this specific rate, for which when i regenerate the IP , i do not get option to select QPLL1  for the RX ( see the drop down shows only QPLL0 ) ?

Such problem does not exist if i select , say 9.8304 or 19.6608 .

Note, I want have TX and RX seperately configurable for different rates, hence having different QPLLs is a necessity,

 

Thanks

Sameer

 

 

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Participant aforencich
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Registered: ‎08-14-2013

回复: GTY serdes QPLL1 for 14.6456 G

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The part datasheet has a better table with all of the line rate ranges.  14.7 only works for QPLL0.  All of the other rates except for 7.3 looks like they should work on any of the QPLLs or even the CPLLs.  7.3728 is half of 14.7456, so you can set the QPLL for 14.7456 and then change the channel divider to get 7.3728.  All the other rates you mentioned look like they'll work on QPLL1. 

The limitation is with the VCOs in the FPGA; the two QPLLs have VCOs with different ranges, and the VCO ranges are not wide enough for the divided outputs to overlap, hence there are gaps in the coverage of each of the QPLLs.  Take a look at the datasheet, the tables in the GTY transceiver section show the line rate ranges for all of the possible output divider settings.  For instance, the VCO in QPLL1 has a range of 8-13 GHz.  With D=1, this supports 16-26 Gbps.  With D=2, this supports 8-13 Gbps.  With D=3, this supports 4-6.5 Gbps.  These ranges don't overlap, so if your rate falls in to one of these ranges, you'll have to use the other QPLL.  It looks like the VCOs on the two QPLLs were designed so that all of the gaps on one are filled in by the other.  Unfortunately, this does mean you can run in to trouble if you want to support two different data rates per GTY quad if both rates happen to only be supported by one QPLL. 

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Xilinx Employee
Xilinx Employee
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Registered: ‎08-25-2010

回复: GTY serdes QPLL1 for 14.6456 G

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Hi @s1gandhi 

VCO operting range for QPLL0 and QPLL1 can be found in table 2-12, ug578:

 

gty_qpll.PNG

Thanks
Simon
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Participant s1gandhi
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Registered: ‎06-24-2019

回复: GTY serdes QPLL1 for 14.6456 G

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so, in this case, if i need to configure the tx and rx serdes at different rates, what is the way out ?

also, for the for the ultrascale + devices, i am able to select qpll1 for 19G for rx. so why the issue is with intermediate range ? is it FPGA limition of some issue with the Wizard ?

thanks

sameer

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Participant s1gandhi
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Registered: ‎06-24-2019

回复: GTY serdes QPLL1 for 14.6456 G

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Just to add to it, i dont see this issue for 12.16512G, 8.11008,9.8304 G rates. but see it only for 14.7456 and 7.3728 rates.

which is not inline with the explanation which you have provided .

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Participant aforencich
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Registered: ‎08-14-2013

回复: GTY serdes QPLL1 for 14.6456 G

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The part datasheet has a better table with all of the line rate ranges.  14.7 only works for QPLL0.  All of the other rates except for 7.3 looks like they should work on any of the QPLLs or even the CPLLs.  7.3728 is half of 14.7456, so you can set the QPLL for 14.7456 and then change the channel divider to get 7.3728.  All the other rates you mentioned look like they'll work on QPLL1. 

The limitation is with the VCOs in the FPGA; the two QPLLs have VCOs with different ranges, and the VCO ranges are not wide enough for the divided outputs to overlap, hence there are gaps in the coverage of each of the QPLLs.  Take a look at the datasheet, the tables in the GTY transceiver section show the line rate ranges for all of the possible output divider settings.  For instance, the VCO in QPLL1 has a range of 8-13 GHz.  With D=1, this supports 16-26 Gbps.  With D=2, this supports 8-13 Gbps.  With D=3, this supports 4-6.5 Gbps.  These ranges don't overlap, so if your rate falls in to one of these ranges, you'll have to use the other QPLL.  It looks like the VCOs on the two QPLLs were designed so that all of the gaps on one are filled in by the other.  Unfortunately, this does mean you can run in to trouble if you want to support two different data rates per GTY quad if both rates happen to only be supported by one QPLL. 

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