Xilinx Constraints Guide

Chapter 4: Xilinx Constraints
FROM-TO (From To)
Architecture Support
Applicable Elements
Propagation Rules
The FROM-TO (From To) constraint:
• Defines a timing constraint between two groups.
• Is associated with the Period constraint of the high or low time.
A group can be user-defined or predefined. From synchronous paths, a FROM-TO
constraint controls only the setup path, not the hold path.
For Virtex®-5 devices, the FROM-TO constraint controls both setup and hold paths.
Applies to all FPGA devices and all CPLD devices.
Predefined and user-defined groups.
Applies to a path specified between two groups.
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 TSname=FROM “group1” TO “group2” value [DATAPATHONLY];
where
• TSname must always begin with TS. Any alphanumeric character or underscore
may follow.
• group1 is the origin path
• group2 is the destination path
• value is ns by default. Other possible values are MHz or another timing specification
such as TS_C2S/2 or TS_C2S*2.
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_PathA = FROM “my_src_grp” TO “my_dst_grp” 23.5 ns
DATAPATHONLY;
XCF Syntax
XST supports FROM-TO with the following limitations:
• FROM-THRU-TO is not supported
• Linked Specification is not supported
• Pattern matching for predefined groups is not supported:
TIMESPEC TS_1 = FROM FFS(machine/*) TO FFS 2 ns;
Constraints Guide
122 www.xilinx.com UG625 (v. 13.2) July 6, 2011