gtkwave

TLDR

Open waveform file

$ gtkwave [dump.vcd]

Open with save file

$ gtkwave [dump.vcd] [signals.gtkw]

Convert FST to VCD

$ vcd2fst [input.vcd] [output.fst]

Open LXT file

$ gtkwave [dump.lxt]

SYNOPSIS

gtkwave [options] [dumpfile] [savefile]

GTKWave is a waveform viewer for digital simulation results. It displays signal traces from VCD (Value Change Dump), FST, LXT, and other formats generated by simulators like Verilator, Icarus Verilog, and GHDL.
The tool provides hierarchical signal browsing, zoom/pan, markers, annotations, and export capabilities for analyzing digital circuit behavior.

PARAMETERS

dumpfile

Waveform file (VCD, FST, LXT, LXT2).

savefile

GTKWave save file (.gtkw).

-o, --optimize

Optimize VCD loading.

-c file

Script file to execute.

-r file

Read RC file.

-S script

Tcl script.

-T

Use Tcl as scripting language.

SUPPORTED FORMATS

- VCD (IEEE 1364)
- FST (Fast Signal Trace)
- LXT, LXT2 (compressed formats)
- GHW (GHDL waveform)
- VZT (compressed VCD)

CAVEATS

Large VCD files may be slow; use FST format. Complex hierarchies need navigation. Memory usage scales with dump size.

HISTORY

GTKWave was written by Tony Bybell as an open-source waveform viewer for digital design verification. It has become the standard viewer for open-source HDL simulators.