02-20-2009 08:01 AM
who can provide the script?
If the current P&R timing is not meet,and the ISE can re-implement based the initial constrain with 0.01ns step add/sub automatic until the timing ok?
So that the ISE can always work no manualy intervention.
02-20-2009 09:21 AM
I'm a little confused by your wording.
Do you mean to vary the timing constraints in steps until the design passes. In that
way to find the "best" achievable timing?
Usually constaints are understood to be absolute requirements. e.g. some external
device MUST have outputs 3 ns before the next clock edge or your design will not
work reliably. Changing the constraints means changing the system level design.
02-21-2009 07:51 PM
02-23-2009 05:29 AM
Generally speaking, reducing the constraint time does not help to meet timing. If you find that
changing timing by .01ns at a time helps, the real mechanism that helps is using a different
random seed for the placement. I would suggest just trying multipass P&R with a constant
constraint value of 8ns. You don't need a special script for this.
03-01-2009 05:07 PM
I only have a critical timing.Eg: my constrain requirement is 8ns.if it is not meet,i wish the script can subtract a 0.01ns step base 8ns.(7.99,7.98,7.97...........) until the timg is ok.then,it can stop.So, i wish get the correct result in the morning through the whole night P&R work .
I'm not sure I see the benefit of your script.
If my period constraint is 8 ns, and if I meet it, I don't care if it can also run at 7.99 ns or whatever.
And if it does NOT run at 8 ns, the fact that it DOES run at 8.1 ns isn't helpful, either.