Xilinx Constraints Guide

Chapter 4: Xilinx Constraints
The name of the H_SET set is derived from the symbol or node in the hierarchy that
includes all the RLOC elements. Inst1 is the node (instantiating macro) that includes
the four flip-flop elements with RLOC constraints shown on the left of the figure.
Therefore, the name of this H_SET set is the hierarchically qualified name of Inst1
followed by h_set.
The Inst1 symbol is considered the start of the H_SET, which gives a convenient handle
to the entire H_SET and attaches constraints that modify the entire H_SET. Constraints
that modify sets are discussed in the Save Net Flag (SAVE NET FLAG) constraint.
This figure demonstrates the simplest use of a set that is defined and confined to a single
level of hierarchy. Through linkage and modification, you can also create an H_SET set
that is linked through two or more levels of hierarchy.
Linkage allows you to link elements through the hierarchy into a single set. On the
other hand, modification allows you to modify RLOC values of the members of a set
through the hierarchy.
RLOC Set Summary
The following table summarizes the RLOC set types and the constraints that identify
members of these sets.
Summary of Set Types
Type Definition Naming Linkage Modification
U_SET= name All elements with
the same user-tagged
U_SET constraint
value are members of
the same U_SET set.
HU_SET= name All elements with the
same hierarchically
qualified name are
members of the same
set.
The name of the
set is the same as
the user-defined
name without
any hierarchical
qualification.
The lowest common
ancestor of the
members is prefixed to
the user-defined name
to obtain the name of
the set.
U_SET links elements
to all other elements
with the same
value for the U_SET
constraint.
HU_SET links to other
elements at the same
node with the same
HU_SET constraint
value. It links to
elements with RLOC
constraints below.
U_SET is modified
by applying
RLOC_ORIGIN
or RLOC_RANGE
constraints on,
at most, one
of the U_SET
constraint-tagged
elements.
The start of the set
is made up of the
elements on the
same node that
are tagged with
the same HU_SET
constraint value. A
RLOC_ORIGIN or
a RLOC_RANGE
constraint can be
applied to, at most,
one of these start
elements of an
HU_SET set.
Constraints Guide
UG625 (v. 13.2) July 6, 2011 www.xilinx.com 251