Using Tcl Scripting 5
UG894 (v2016.3) October 5, 2016
www.xilinx.com
A Brief Overview of Tcl
commands in the Vivado Design Suite Tcl Command Reference Guide (UG835) [Ref 1], or in
the Help system of the Vivado tools.
The Vivado IDE uses Xilinx Design Constraints (XDC) to specify the design constraints. XDC
is based on a subset of all the Tcl commands available in Vivado and is interpreted exactly
like Tcl. The XDC commands are primarily timing constraints, physical constraints, object
queries and a few Tcl built-in commands: set, list, and expr. For a complete description
of the XDC commands, see Appendix B of the Vivado Design Suite User Guide: Using
Constraints (UG903) [Ref 3]. Unlike Tcl scripts, XDC files are managed by the Vivado IDE so
that any constraint edited through the graphical interface or the Timing Constraints Editor
can be saved back to its original XDC file. For this reason, only XDC commands can be used
in a XDC file. If you need to use other Tcl commands to write your constraints, you must use
a Tcl script.
The Vivado tools write a journal file called vivado.jou into the directory from which
Vivado was launched. The journal is a record of the Tcl commands run during the session
that can be used as a starting point to create new Tcl scripts.
A log file, vivado.log is also created by the tool and includes the output of the commands
that are executed. Both the journal and log file are useful to verify which commands were
run and what result they produced.
Additional Tcl commands are provided by the Tcl interpreter that is built into the Vivado
Design Suite. For Tcl built-in commands, Tcl reference material is provided by the Tcl
Developer Xchange website, which maintains the open source code base and
documentation for Tcl, and is located at http://www.tcl.tk
See http://www.tcl.tk/man/tcl8.5/tutorial/tcltutorial.html [Ref 8] for an introductory tutorial
to the Tcl programming language. Also see the Tclers Wiki located at http://wiki.tcl.tk
for
some example scripts.
In this document you will see some examples of Tcl commands and Tcl scripts, and the
results that are returned by the Vivado Design Suite when these commands are run. The
commands and their return values appear with the following formats:
• Tcl commands and example scripts:
puts $outputDir
• Output to Tcl Console or results of Tcl commands:
./Tutorial_Created_Data/cpu_output
A Brief Overview of Tcl
A Tcl script is a series of Tcl commands, separated by new-lines or semicolons. A Tcl
command is a string of words, separated by blanks or tabs. The Tcl interpreter breaks the
UG894 (v2016.4) November 30, 2016
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