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Explorer
Explorer
10,183 Views
Registered: ‎11-27-2008

Virtex 5 GTP Rocket IO Multiple Clock selection

I need to select between two different external reference clocks for the GTP Rocket IO tile, 156.25MHz and 125MHz. What would be the best/cleanest way to do this? Both reference clocks would be coming from external differential oscillators (thus very low jitter) and I would select which would feed the Rocket IO reference tile. Can I just use the simple global clock mux selector or do I need to do something more fancy, such as two DCMs and a PLL (to clean up jitter)?

 

Thanks,

Dan

 

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5 Replies
Instructor
Instructor
10,169 Views
Registered: ‎08-14-2007

Re: Virtex 5 GTP Rocket IO Multiple Clock selection

I have done this exact thing, but I used an external 2:1 LVDS multiplexer to allow

use of the GTP direct reference clock input.  I would not suggest using fabric

clocks as a GTP reference.

-- Gabor
Xilinx Employee
Xilinx Employee
10,099 Views
Registered: ‎08-07-2007

Re: Virtex 5 GTP Rocket IO Multiple Clock selection

consider ICS85401, which is a clock mux that is used for GTPs' ref clocks on ML50x demo board.

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Visitor chichu
Visitor
10,052 Views
Registered: ‎02-25-2009

Re: Virtex 5 GTP Rocket IO Multiple Clock selection

"consider ICS85401, which is a clock mux that is used for GTPs' ref clocks on ML50x demo board."

 

Are they die ports J20 and J21 for ML505?

 

ist it right?
################ Init Clock Constraint #########################

NET INIT_CLK        LOC=AH15;   #100 Mhz Oscillator

################ GTP CLOCK Locations of the pins##############

NET GREF_CLK_P  LOC=j20;
NET GREF_CLK_N  LOC=j21;
##########################################################
Message Edited by chichu on 02-25-2009 08:01 AM
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Explorer
Explorer
9,885 Views
Registered: ‎11-27-2008

Re: Virtex 5 GTP Rocket IO Multiple Clock selection

Thanks for the suggestions.

 

A related question.....I also need to switch between a 20/16 bit and 10/8 bit interface on the Rocket I/O. Can I do this using the DRP configuration port? Otherwise I have to add some staging logic to take a 16 bit 1x clock rate interface and change it to an 8 bit 2x clock rate interface. I'd rather not do that.

 

Thanks,

Dan

 

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Newbie vila
Newbie
9,788 Views
Registered: ‎02-17-2009

Re: Virtex 5 GTP Rocket IO Multiple Clock selection

oh,this tips is too old now.

 

 

 

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