Xilinx Constraints Guide

TIMEGRP (Timing Group)
The TIMEGRP (Timing Group) constraint:
Chapter 4: Xilinx Constraints
• Uses the Timing Name (TNM) identifier to group design elements together for
timing analysis.
• Allows you to:
Architecture Support
Applicable Elements
– Define groups in terms of other groups
– Create a group that is a combination of existing groups
– Place TIMEGRP constraints in a User Constraints File (UCF) or a Netlist
Constraints File (NCF)
Applies to all FPGA devices and all CPLD devices.
• Design elements
• Nets
Propagation Rules
Syntax
Applies to all elements or nets within the group.
The following examples show how to use this constraint with particular tools or
methods. If a tool or method is not listed, you cannot use this constraint with it.
Syntax Examples
Combining Multiple Groups into One
You can define a group by combining other groups.
Multiple Groups UCF Syntax Example One
The following syntax example illustrates the simple combining of two groups.
TIMEGRP “big_group”="small_group” “medium_group”;
In this syntax example, small_group and medium_group are existing groups defined using
a TNM or TIMEGRP attribute.
Multiple Groups UCF Syntax Example Two
A circular definition, as shown below, causes an error when you run your design
through NGCBuild:
TIMEGRP “many_ffs”=”ffs1” “ffs2”;
TIMEGRP “ffs1”=”many_ffs” “ffs3”;
Constraints Guide
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