read_xdc - 2020.2 English

Vivado Design Suite Tcl Command Reference Guide (UG835)
Document ID
UG835
Release Date
2020-11-18
Version
2020.2 English

read physical and timing constraints from one of more files.

Syntax

read_xdc [‑cells <args>] [‑ref <arg>] [‑quiet_diff_pairs] [‑mode <arg>]
    [‑unmanaged] [‑no_add] [‑quiet] [‑verbose] <files>

Returns

list of files

Usage

Name Description
[-cells] Import constraints for these cells
[-ref] Import constraints for this ref
[-quiet_diff_pairs] Suppress warnings about differential pair inference when importing I/O ports
[-mode] Import constraints as out_of_context. Values: default, out_of_context Default: default
[-unmanaged] treat this file as unmanaged constraints file
[-no_add] don't add this file to constraints fileset
[-quiet] Ignore command errors
[-verbose] Suspend message limits during command execution
<files> Input file(s) to read

Categories

FileIO

Description

Imports physical and timing constraints from a Xilinx Design Constraints file (XDC). The XDC is imported into the current_instance level of the design hierarchy, which defaults to the top-level of the design, or can be imported into specified cells. When imported at the top-level, the specified XDC file is added to the active constraint fileset.
Important: Constraints from the XDC file will overwrite any current constraints of the same name. Therefore, exercise some caution when reading a XDC file to be sure you will not overwrite important constraints.

This command is similar to the add_files command in that the XDC file is added by reference rather than imported into the local project directory.

You can use this command to read the contents of source files into the in-memory design, when running the Vivado tool in Non Project mode, in which there is no project file to maintain and manage the various project source files. Refer to the Vivado Design Suite User Guide: Design Flows Overview (UG892) for more information on Non Project mode.

Arguments

-cells <args> - (Optional) Apply the constraints from the XDC file to the specified instance names. The constraints will be applied ONLY to the specified cell instances, and the XDC file will not be added to the active constraint fileset.
Tip: A design must be open when specifying the -cells option.

-ref <arg> - (Optional) Read the constraints from the XDC file and apply them to ALL instances of the referenced module, wherever they happen to be instantiated in the current design.

-quiet_diff_pairs - (Optional) Suppress warnings about differential pair inference when importing I/O constraints.

-mode [ default | out_of_context ] - (Optional) Import the specified constraint files as in-context with the top-level design, or as out_of_context constraints to be used when generating output products for hierarchical modules or IP cores. For more information on the out-of-context design flow, refer to the Vivado Design Suite User Guide: Design Flows Overview (UG892).
Important: Out-of-context constraints should be added to specified cells or cell instances.

-unmanaged - (Optional) Treat the added files as unmanaged Tcl constraint files. The Vivado tool will not save constraint changes back into these unmanaged Tcl files. For more information on unmanaged Tcl constraints, refer to the Vivado Design Suite User Guide: Using Constraints (UG903).

-no_add - (Optional) Read the constraints from the file, and integrate them into the in-memory design, but do not add the XDC file to the list of files in the current constraint set.

-quiet - (Optional) Execute the command quietly, returning no messages from the command. The command also returns TCL_OK regardless of any errors encountered during execution.
Note: Any errors encountered on the command-line, while launching the command, will be returned. Only errors occurring inside the command will be trapped.
-verbose - (Optional) Temporarily override any message limits and return all messages from this command.
Note: Message limits can be defined with the set_msg_config command.
<files> - (Required) The filenames of the XDC files to be imported.
Note: If the path is not specified as part of the file name, the tool will search for the specified file in the current working directory and then in the directory from which the tool was launched.

Examples

The following example reads the XDC file and applies it to the current design: 
read_xdc file_1.xdc
The following example reads the XDC file and applies it ALL instances of the referenced module found in the current design: 
read_xdc -ref hex2led file_2.xdc
The following example reads the XDC file and applies it ONLY to the specified instance within the referenced module: 
read_xdc -ref sixty -cells lsbcount file_3.xdc
The following example reads the XDC file and applies it to the specified instances in the current design, even though they are instances of different modules: 
read_xdc -cells {one_decode sixty/msbcount} file_4.xdc
Note: Multiple cells must be enclosed in quotes, "", or braces, {}.

See Also