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6,456 Views
Registered: ‎08-30-2007

the problem of offset in constraints

 

 when I set the offset in constraints, no matter how much I set the value is, at last, the timing analyzer will ignore the constraints, why? when set the "offset in" constraints, what need to consider more than "offset out" constaints?

 

 

thanks,

Jie 

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3 Replies
Xilinx Employee
Xilinx Employee
6,423 Views
Registered: ‎11-28-2007

Re: the problem of offset in constraints

Two things: 1. the reference clock needs to come from an external clock input. 2. the clock used to register the input can be traced back to the reference clock input (via DCM, PLL, BUFG, etc).

 

Cheers,

Jim

 

Cheers,
Jim
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Xilinx Employee
Xilinx Employee
6,374 Views
Registered: ‎08-13-2007

Re: the problem of offset in constraints

You may also find this a useful reference:

http://www.xilinx.com/support/documentation/white_papers/wp237.pdf (What are OFFSET Constraints?)

 

bt

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Xilinx Employee
Xilinx Employee
6,025 Views
Registered: ‎08-10-2008

Re: the problem of offset in constraints

Does any information indicate why it is ignored? This is always caused by no timing group found.
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