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Chapter 12: TRACE
R
OFFSET IN Constraint Examples
This section describes in detail a specific example of an OFFSET IN constraint as shown in
the Timing Constraints section of a timing analysis report. For clarification, the OFFSET IN
constraint information is divided into the following parts:
• OFFSET IN Header
• OFFSET IN Path Details
• OFFSET IN Detailed Path Data
• OFFSET IN Detail Path Clock Path
• OFFSET IN with Phase Clock
OFFSET IN Header
The header includes the constraint, the number of items analyzed, and number of timing
errors detected. Please see PERIOD Header for more information on items analyzed and
timing errors.
Example:
======================================================================
Timing constraint: OFFSET = IN 4 nS BEFORE COMP "wclk_in" ;
113 items analyzed, 30 timing errors detected.
Minimum allowable offset is 4.468ns.
----------------------------------------------------------------------
The minimum allowable offset is 4.468 ns. Because this is an OFFSET IN BEFORE, it means
the data must be valid 4.468 ns before the initial edge of the clock. The PERIOD constraint
was defined with the keyword HIGH, therefore the initial edge of the clock is the rising
edge.
OFFSET IN Path Details
This path fails the constraint by 0.468 ns. The slack equation shows how the slack was
calculated. In respect to the slack equation data delay increases the setup time while clock
delay decreases the setup time. The clock arrival time is also taken into account. In this
example, the clock arrival time is 0.000 ns; therefore, it does not affect the slack.
Example:
======================================================================
Slack: -0.468ns (requirement - (data path - clock path
- clock arrival + uncertainty))
Source: wr_enl (PAD)
Destination: wr_addr[2] (FF)
Destination Clock: wclk rising at 0.000ns
Requirement: 4.000ns