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Chapter 3: Timing Constraint Principles
The TIMEGRP attribute is to combine existing time groups (pre-defined or user-defined)
together or remove common elements from existing time groups, and create a new userdefined time group. The TIMEGRP attribute is also a method for creating a new time group
by pattern matching (grouping a set of objects that all have output nets that begin with a
given string).
Use the following keywords to create subsets of an existing time group:
•
Rising edge synchronous elements (RISING)
•
Falling edge synchronous elements (FALLING)
•
Remove common elements (EXCEPT)
Use the EXCEPT keyword with a TIMEGRP attribute to remove elements from an alreadycreated time group. The overlapping items to be removed from the original time group
must be in the excluded or EXCEPT time group. If the excluded time group does not
overlap with the original time group, none of the design elements are removed. In that
case, the new time group contains the same elements as the original time group.
In addition to using TIMEGRP to include multiple time groups or exclude multiple time
groups, it also can be used to create sub-groups using the RISING and FALLING
keywords. Use RISING and FALLING to create groups based upon the synchronous
element triggered clocking edge (rising or falling edges).
Pattern Matching
Pattern matching on either net or instance names can define the user-defined time group.
Use wildcard characters to define a user-defined time group of symbols whose associated
net name or instance name matches a specific pattern. Wildcards are used to generalize the
group selection of synchronous elements. Wildcards can also be used to shorten and
simplify the full hierarchical path to the synchronous elements.
Pattern matching is as follows:
•
Asterisk (*)
Matches any string of zero or more characters
•
Question Mark (?)
Matches a single character
Table 3-2:
Pattern Matching Examples
String
Indicates
Examples
DATA*
any net or instance name that
begins with DATA
DATA1, DATA22, and
DATABASE
NUMBER?
any net names that begin
with NUMBER and ends with
one single character
NUMBER1 or NUMBERS, but
not NUNMBER or NUMBER12
A pattern may contain more than one wildcard character. For example, *AT? specifies any
net name that:
42
•
Begins with one or more characters followed by AT, and
•
Ends with any one character
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Timing Constraints User Guide
UG612 (v 11.1.1) April 29, 2009