Generating and Waiving Design Checks - 2023.2 English

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

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2023.2 English

The waiver mechanism provides the ability to waive CDC, DRC, and Methodology violations. After a violation is waived, it is not reported anymore by the report_cdc, report_drc, and report_methodology commands. Waived DRCs are also filtered out from the mandatory DRCs which are run as a prerequisite for the implementation commands such as opt_design, place_design, phys_opt_design, route_design or write_bitstream.

Waivers are XDC compatible and can be imported through the commands, read_xdc or source. They can be included in any XDC file or Tcl script, in Project or Non-Project modes. They can be created from the top-level or scoped to a hierarchical module. After waivers are added to the design, they are automatically saved inside the checkpoint and restored when the checkpoint is reloaded. The waivers can be written out with the commands, write_xdc and write_waivers.

Waivers provide tracking capabilities. Vivado tools record the user who creates the waivers, the date and time of creation, as well as a short description. This information is important for tracking purposes. It is recommended that all the waivers applied to the design are reviewed and verified to ensure that they are valid.

Waivers are first class objects that can be created, queried, reported on, and deleted. Waivers reference other first class objects returned by the Vivado get_* commands, such as pins, cells, nets, Pblocks, and sites. These objects must exist in the design prior to creating the waivers. Design objects that do not exist at the time of waiver creation are not covered by the waivers.

Important: Similar to other constraints, it is recommended to create the waivers on a post-synthesized design. Waivers that are created on post-implemented designs could reference design objects that do not exist inside the post-synthesis netlist. Such waivers are discarded if they are applied on the post-synthesis design.

The waiver mechanism supports replication and deletion of netlist objects. When an object involved in a waiver is replicated, the replicated object is automatically added to the waiver. Similarly, when an object is deleted, any reference to it is automatically removed from the waivers. When the deleted object results in a waiver referencing an empty list of objects, the waiver is deleted from the in-memory design and is not saved in the subsequent checkpoints. The same mechanism applies to timing constraints and clock objects. When a clock gets deleted through logic optimization or by removing the timing constraints (reset_timing), any waiver referencing the clock object gets deleted and is not saved in the subsequent checkpoints.

Note: The Vivado commands rename_net, rename_cell, rename_port, and rename_pin do not rename the design elements inside the waiver. If a waiver refers to a netlist element renamed by one of these commands, the waiver becomes invalid because it still refers to the design element's original name.
Note: Custom Design Rule Checks cannot be waived. For more information about user written DRCs, refer to this link in the Vivado Design Suite User Guide: Using Tcl Scripting (UG894).