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Observer
Observer
8,514 Views
Registered: ‎12-10-2010

Applying MAXSKEW to specific loads on a net

How can that be done? Let’s say that the input net "rx_net" has 6 loads (registers) A, B, C, D, E and F and I need to constrain the skew between A, B, C and D, but not E and F. Is there a way to accomplish this with the MAXSKEW constraint? Using TIG somehow?

 

/B

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Xilinx Employee
Xilinx Employee
8,508 Views
Registered: ‎08-01-2012

The skew calculation uses a combination of MAX and[Relative] MIN as follows:

 

SKEWhold = Max(DST clock delay)- Min(SRC clock delay)
SKEWsetup = Min(DST clock delay)- Max(SRC clock delay)

 

The below link give some useful information (For 11.X tools example)  http://www.xilinx.com/support/documentation/sw_manuals/xilinx11/pce_p_exceptions_maxdelayskew.htm 

 

Also refer below link documents

 

http://www.xilinx.com/itp/xilinx10/books/docs/timing_constraints_ug/timing_constraints_ug.pdf 

http://www.xilinx.com/support/documentation/white_papers/wp257.pdf

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Observer
Observer
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Registered: ‎12-10-2010

I've looked in the Constraints Guide several times and haven't found anything that applies to my situation. Maybe I'm not looking hard enough...

 

Note that it is the skew between the data paths to the registers that I'm trying to constrain. Well, four out of the six paths. I don't want to constrain two of the paths and that's the problem.

 

The constraint I have is:

 

NET "rx_net" MAXSKEW = 0.5 ns;

 

This constraint applies to all paths leading to A, B, C, D, E and F. How can I "unconstrain" the paths to E and F?

 

/B

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Observer
Observer
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Registered: ‎12-10-2010

I'd like to give this question a little bump. I still haven't found a solution...
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