Open a Value Change Dump (VCD) file for capturing simulation output. This Tcl command models behavior of $dumpfile Verilog system task
Syntax
open_vcd [‑ports] [‑quiet] [‑verbose] [<file_name>]
Returns
Returns a Vcd Object and sets the current vcd to this object so that current_vcd command will return this object.
Usage
Name | Description |
---|---|
[-ports]
|
Open extended VCD file for ports dumpping. Defaults to dumpports.vcd. |
[-quiet]
|
Ignore command errors |
[-verbose]
|
Suspend message limits during command execution |
[<file_name>]
|
file name. Defaults to dump.vcd (This is LRM standard) Default: dump.vcd |
Categories
Description
Create or open a Value Change Dump (VCD) file to capture simulation output. This command operates like the Verilog $dumpfile
simulator directive.
VCD is an ASCII file containing header information, variable definitions, and value change details of a set of HDL signals. The VCD file can be used to view simulation result in a VCD viewer or to estimate the power consumption of the design.
When a VCD file has been opened, you can write the value changes from the simulation into the VCD file using checkpoint_vcd
, flush_vcd
, or log_vcd
. In addition, you can pause and resume the collection of value change data with the stop_vcd
and start_vcd
commands.
You can limit the size of the VCD file by using the limit_vcd
command.
To close the VCD file, use the close_vcd command.
open_vcd
command before using any other *_vcd
commands. Only one VCD file can be open at any time.Arguments
-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.
-verbose
- (Optional) Temporarily override any message limits and return all messages from this command.
set_msg_config
command.
<file_name>
- (Optional) Is the name of the file into which to dump the current VCD information. When a filename is not specified, the default filename of dump.vcd is used. If the specified VCD file already exists, then open_vcd
resets the VCD file to a new state, overwriting the current contents.
Examples
log_vcd
command identifies all ports in the /tb/UUT scope, and only that level of the design hierarchy, to be written to the VCD file. The simulation is run for a specified period of time, and flush_vcd
writes the current values of the HDL objects to the VCD file. Then close_vcd
closes the open file.
open_vcd design1.vcd
log_vcd -level 1 [get_objects filter { type == port } /tb/UUT/* ]
run 1000
flush_vcd
close_vcd