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AR# 36205

MAP/Constraints System - MAP hangs during "Updating Timing Models" due to large grouping constriant

Description

When running the design through Map, it hangs while running "Updating Timing Models".

If the following constraint is commented out, map completes without any errors.
 

TIMEGRP "TG_NotRegIntFFS" = FFS(*) EXCEPT FFS( "embswitch/*regInt*/*" ).



Why does this happen?

Solution

MAP hangs because the Constraints System is unable to handle the timing groups that consist of large amount of BELs and are used in several FROM TO constraints.

In this example, FFS(*) returns 23034 instances while FFS("embswitch/*regInt*/*") returned 2616 instances.

So this group would be 20 K of FFs.

This timing group is also used for FROM TO constraints in several places.

So commenting this group out will also cancel all of the FROM TO constraints as the group won't exist.


The way in which the FFs have been grouped is causing too many constrained paths for the timing algorithm to handle.

Note that the FROM TO constraints are normally used as 'exception' paths from a period constraint, i.e out of the timing group constrained by a period constraint, some take FROM TO.

To resolve this issue, use one main period and some FROM TOs if possible, preferably defined by clocks not by FFS/EXCEPT keywords.


We have also see that the SDC to UCF converter that some EDA companies provide will create several constraints that have multiple wildcards.

If these UCF files can be simplified or each constraint with several wildcards is split up into several constraints with less wildcards per constraint, then the run time should go down.

Also if there are more than eight wild card numbers in a constraint, the Constraints system is unable to handle this and will hang during map when updating timing models.

One way to work around this issue is to make individual time groups and use FROM TO constraints to write out the constraints without using the wild cards.
AR# 36205
Date Created 06/14/2010
Last Updated 09/03/2014
Status Active
Type Known Issues
Tools
  • ISE Design Suite