generate_vcd_ports - 2025.2 English - UG900

The generate_vcd_port command opens a VCD file handle for writing port activity of the given instance. This VCD file is read by create_testbench Tcl command to read port activity for writing the stimuli source. You can select the instance from the scope window in Vivado simulator IDE. Alternatively, specify the hierarchical path to the instance when executing the generate_vcd_port command from Tcl console. The command creates dummports.vcd file that gets populated when running simulation for the selected instance scope.

If running this command from Vivado IDE, then the dumpports.vcd file is created in the simulation run directory. If running this command from Vivado simulator standalone GUI, then the dumpports.vcd file is created in vcd2tb sub-directory of the current directory. Following are the generate_vcd_port options:

-scope <arg> (required)

Specify the instance scope hierarchy name.

-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 are returned. Only errors occurring inside the command are 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.

The following example command generates a VCD file for the /top/DUT/fifo/buf_1 instance of the buf module. It records waveform activity for 2000 ns and then, closes the VCD file handle:

generate_vcd_ports {/top/DUT/fifo/buf_1}
run 2000ns
close_vcd -ports