set_disable_timing - 2024.1 English

Vivado Design Suite Tcl Command Reference Guide (UG835)

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2024.1 English

Disable timing arcs


set_disable_timing [‑from <arg>] [‑to <arg>] [‑quiet] [‑verbose] <objects>


Name Description
[-from] From pin on cell
[-to] To pin on cell
[-quiet] Ignore command errors
[-verbose] Suspend message limits during command execution
<objects> List of cells or pins, ports, lib-cells, lib-pins, libcell/cell timing-arcs


SDC, XDC, Timing


Disables timing arcs within a specified cell or cells that lead to the output pins of the cell. Only the I/O paths between the clock port and the outputs of the cell are disabled.

The purpose of disabling a timing arc is to prevent timing analysis through the arc.

If a <cell> is specified, then all timing arcs in that cell are disabled. If the optional -from and -to arguments are specified, then the timing arcs are defined by the from/to pins. If only -from is speified then all timing arcs from that pin are disabled. If only -to is specified then all timing paths to that pin are disabled.

If a <port> is specified, then all timing paths from a specified input port are disabled, or timing paths to a specified output port are disabled.

Note: This command operates silently and does not return direct feedback of its operation


-from <pin_name> - (Optional) Specifies the source pin of an object cell. The pin_name is specified by name only, without the need for the hierarchical cell name, which is defined by the <object>.

-to <pin_name> - (Optional) Specifies the destination pin of an object cell. The pin_name is specified by name only, without the need for the hierarchical cell name, which is defined by the <object>.

-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.

<objects> - (Required) A list of one or more objects on which to disable the timing arcs. Must be specified as Vivado™ objects returned by get_cells or other appropriate Tcl commands. Can be any of the following types of objects: cells, ports, pins, lib-cells, lib-pins, lib-cell/cell timing arcs.


The following example disable the timing arc between the pins I0 and O of the LUT div_dec_ff_i/U0/count_i_1 to break a combinational loop:

set_disable_timing -from I0 -to O [get_cells div_dec_ff_i/U0/count_i_1]

The following example disables the timing arcs between the specified input pin to the specified output pin of a Block RAM cell:

set_disable_timing -from WEBWE[3] -to CLKMEM [get_cells \

The following example disables all timing arcs of the specified cell:

set arcs [get_timing_arcs -of_objects [get_cells \
set_disable_timing $arcs