The Timing Constraints Wizard recommends missing constraints that define clocks or refer to clocks, which will be saved either at the end of the target XDC file in project mode, or at the end of all constraints in other modes. For this reason, you must understand the following rules:
- Project mode
- You must specify a target XDC file with its processing order set to NORMAL
before launching the Timing Constraints wizard. The target XDC file must belong
to the Constraints Set of the design open in memory and currently selected. The
position of the target XDC file among the other XDC files matters because it
specifies where the recommended constraints will be applied and saved later.
Also, the wizard tries to re-apply any invalid constraint that belongs to XDC
files parsed after the target XDC file in order to provide the most complete and
For example, consider the netlist from synth_1 run open in memory with the Constraints Set constr_1. This Constraints Set contains three XDC files in the sequence a.xdc, b.xdc, and c.xdc. If you choose b.xdc as the target XDC file and each file contains an invalid constraint, the Timing Constraints wizard applies the recommended clocks, then re-applies the invalid constraints from c.xdc before proceeding to the next step and discovering other missing constraints.
- Non-project or Design Check Point (DCP) modes
- You cannot specify a target XDC file in these modes, so the Timing Constraints
wizard recommends and applies new constraints at the last position of the
constraints sequence. This is equivalent to entering new constraints in the Tcl
Console or via the Timing Constraints window. In these modes, the wizard does
not attempt to re-apply invalid constraints. If the new constraints need to be
applied earlier in the overall constraints sequence in order to resolve
constraints dependencies or precedence issues, you must edit the constraints
Here is an example of how to manually edit constraints.
- Create new constraints using the Vivado Design Suite.
- Run one of the following
write_xdc -exclude_physical timing_constraints.xdc write_xdc -type timing timing_constraints.xdc
- Edit timing_constraints.xdc to move the new constraints higher in the XDC file.
- Save the file.
- Run the following
- Read the edited timing constraints file by
You can review the updated timing constraints sequence using the Timing Constraints window. After reviewing the new constraints, you can save the sequence into the DCP.