Exceptions Section - 2023.2 English

Vivado Design Suite User Guide: Design Analysis and Closure Techniques (UG906)

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2023.2 English

This section provides access to the detailed table of each timing exception. A category is available for each type of timing exceptions and the categories are hyperlinked from the Summary table. The format of the detailed tables depends on whether the Coverage option has been selected in the GUI or not.

Following is an example of a detailed table without the Coverage option selected.

Figure 1. Report Exceptions: Detailed Table without Coverage

The table column Position represents the timing constraint position number that matches the position number reported by the Timing Constraints Editor (TCE). You can double-click on a row to be redirected to the selected constraint inside TCE. An alternative is to right-click on the row and select View Constraint from the popup menu.

Figure 2. Report Exceptions Context Menu

The image below shows the selected constraint inside the Timing Constraint Editor (TCE).

Figure 3. Timing Exception inside Timing Constraint Editor

The columns From, Through, and To report the original patterns used to define the timing exception. You can also refer to the constraint position number inside the TCE to review the same patterns.

The following figure shows an example of a detailed table with the Coverage option selected inside the Report Exception GUI.

Figure 4. Report Exceptions: Detailed Table with Coverage

The table column Position represents the timing constraint position number as described above.

When the Coverage option has been selected, the table columns From, To, and Through include hyperlinks to the design objects targeted by the timing constraints. The objects can be cells, nets, pins, ports, or clocks. It is possible to click on the blue hyperlinks to select the objects. After the objects have been selected, the schematic can be opened with the F4 key. In addition, the coverage information adds the table columns From (%), To (%), and Through (%) that indicate the coverage percentage.

The table column Status reports the status of the constraint such as Invalid endpoint, Partially overridden path, Non-existent path, or Totally overridden. The same status is reported when report_exception is run on the command line:

  • Non-existent path: The exception is considered invalid (does not impact timing analysis).
  • Totally overridden: The exception is considered invalid (does not impact timing analysis).
    Note: The coverages are calculated in the following order: From, Through, and To. The coverage computed for a level depends on the previous level. When the calculated coverage is 0% for a given level, all sub-sequent levels inherit the 0% coverage.
    Note: A constraint with 0% coverage can be considered invalid because it does not impact timing analysis.
    Note: Pins tied to VCC/GND are reported as invalid pins.

The Clock Groups are not defined with -from, -through, and -to and therefore, the detailed table is different.

Figure 5. Detailed Table for Clock Groups

When a Clock Group constraint involves multiple groups and each group has multiple clocks, the table includes one row per clock-pair for all the possible combinations of clock-pairs. In this scenario, the constraint spans over multiple rows and each row refers to the same constraint position number.

The constraint position number 443 in the above design is defined as:

set_clock_groups -physically_exclusive -group RFSCLK -group LB_MD1SFSCLK

The constraint spans over two rows because some timing paths exist from clock RFSCLK to clock LB_MD1SFSCLK and from clock LB_MD1SFSCLK to clock RFSCLK.