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Explorer
Explorer
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GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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why to select 156.25MHz for kcu105 10G ethernet subsystem from ug921?

why to select 161.1328125MHz for VCU118 10G ethernet subsystem from vivado 2017.4 ip catlog?

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Xilinx Employee
Xilinx Employee
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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Hi

 

The reference clock provided should match the selected value.

 

So you need to provide input clock of 161.13Mhz by programming the silas oscillator in board flow for 10G on the VCU118 board

 

Regards,

Satish

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Explorer
Explorer
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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should i supply 156.25MHz or 161.1328125MHz refclk for 10G ethernet at vcu118 board?

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Moderator
Moderator
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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Please supply the refclk at the frequency selected in the design.
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Explorer
Explorer
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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why different?

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Xilinx Employee
Xilinx Employee
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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Hi, default will change with line rate selected. If 10G/25G Ethernet Subsystem is configured for 25G operation it will default to 161.x Mhz reference clock.  If the core is configured for 10G operation it will default to 156.25Mhz refclk.  In GUI drop down user can select different frequency.

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Moderator
Moderator
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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I believe the difference is the encoding.  64/66 encoding changes the rate.  66*156.25 / 64 = 161.1328125.

Roy


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Explorer
Explorer
1,254 Views

Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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@roym

 

why to select 156.25MHz for kcu105 10G ethernet subsystem from ug921?
why to select 161.1328125MHz for VCU118 10G ethernet subsystem from vivado 2017.4 ip catlog?

 

@ejanney it is 161.1328125 for 10G.

 

do i need config the si5370 clock freq from 156.25 to 161.1328125 MHz?

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Xilinx Employee
Xilinx Employee
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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Hi

 

The 10G/25G Ethernet Subsystem core as such doesn't have any fixed clocking requirements and you can select any of the available clocks as shown in below snapshot.

 

xxv_vcu118.png

 

The restriction comes when you select Gt Bank and GT clock in the board parameters tab.

 

Board flow doesn't have the line rate input and as GTY is supported the default is 25G and the corresponding clock default clock is 161.1328Mhz will be selected and other options of clocks will be greyed out.

 

So if you are using board flow then you need to provide 161.13Mhz clock by programming the silas oscillator even for 10G.

 

If you want to use default 156.25Mhz then leave board interface as custom and then generate the core by selecting the reference clock to 156.25Mhz

 

Regards,

Satish

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Explorer
Explorer
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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why can't  the refclk be changed from 161.1328Mhz to  156.25MHz even if i select 10G with board flow ?

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Xilinx Employee
Xilinx Employee
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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Hi

 

Currently the board flow has only option of default line rate and clocks for the GTY based devices.

 

Even if you change the line late it doesn't take this as an input to change the default clock or to put in an other way board flow supports only 161.13Mhz for now on the VCU118 board.

Regards,

Satish

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Explorer
Explorer
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Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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so,should i supply 156.25MHz or 161.1328125MHz  refclk with board flow for 10G mode?

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Xilinx Employee
Xilinx Employee
1,347 Views

Re: GT_REFCLK: 156.25MHz or 161.1328125MHz for 10G ethernet system

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Hi

 

The reference clock provided should match the selected value.

 

So you need to provide input clock of 161.13Mhz by programming the silas oscillator in board flow for 10G on the VCU118 board

 

Regards,

Satish

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Kindly note- Please mark the Answer as "Accept as solution" if information provided is helpful.

Give Kudos to a post which you think is helpful.
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