Xilinx Constraints Guide

Chapter 4: Xilinx Constraints
FROM-THRU-TO (From Thru To)
Architecture Support
Applicable Elements
Propagation Rules
The FROM-THRU-TO constraint:
• Is an advanced timing constraint,
• Is associated with the Period constraint of the high or low time.
From synchronous paths, a FROM-TO-THRU constraint controls only the setup path,
not the hold path. This constraint applies to a specific path that begins at a source
group, passes through intermediate points, and ends at a destination group. The source
and destination groups can be either user or predefined groups. You must define an
intermediate path using TPTHRU before using THRU.
Applies to FPGA devices. Does not apply to CPLD devices.
Predefined and user-defined groups
Applies to the specified FROM-THRU-TO path only.
Syntax Examples
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.
UCF and NCF Syntax
TIMESPEC “TSidentifier”=FROM “source_group” THRU “thru_pt1”...[THRU “thru_pt2”
...] TO “destination_group” value [Units] [DATAPATHONLY];
where
• identifier can consist of characters or underbars
• source_group and destination_group are user-defined or predefined groups
• thru_pt1 and thru_pt2 are intermediate points to define specific paths for timing
analysis
• value is the delay time
• units can be ps, ms, ns, or micro
The DATAPATHONLY keyword indicates that the FROM-TO constraint does not take
clock skew or phase information into consideration. This keyword results in only the
data path between the groups being constrained and analyzed.
TIMESPEC TS_MY_PathB = FROM “my_src_grp” THRU “my_thru_pt” TO “my_dst_grp” 13.5 ns DATAPATHONLY;
FROM or TO is optional. You can have just a FROM or just a TO.
Constraints Guide
120 www.xilinx.com UG625 (v. 13.2) July 6, 2011