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amin_8460
Visitor
Visitor
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Registered: ‎11-27-2012

Specifying Timing Constraints in XST

Hi

In the UG612, it has been mentioned we can specify timing constraint in HDL or ucf file. Is there any diffrence between these two specifying?

If yes which one is better?

 

thanks

Amin

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bassman59
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Registered: ‎02-25-2008


@amin_8460 wrote:

Hi

In the UG612, it has been mentioned we can specify timing constraint in HDL or ucf file. Is there any diffrence between these two specifying?

If yes which one is better?

 

thanks

Amin


Always specify constraints in the UCF. They don't belong in the source code.

----------------------------Yes, I do this for a living.
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sampatd
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Scholar
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Registered: ‎09-05-2011

Hi, 

 

If you are specifying the constraints in the HDL, and wish to change them during the design cycle - you will need to re-synthesize the design. Whereas, constraints specified in a UCF file taken in by the tool in the Translate(ngdbuild) stage, which is a post synthesis step, allow you to use the original netlist (ngc) thereby obviating the need to synthesize again. 

 

Regards,

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