Waveform Guide

Generate VCD and FST waveform output for signal inspection in GTKWave.

RyuSim can generate waveform output in VCD and FST formats for viewing signal activity in tools like GTKWave.

Enable waveform output

Set WAVES=1 in your Makefile for VCD output:

SIM            ?= ryusim
TOPLEVEL_LANG  := verilog

VERILOG_SOURCES = $(PWD)/counter.sv
TOPLEVEL        = counter
COCOTB_TEST_MODULES = test_counter

# Enable VCD waveform output
WAVES = 1

include $(shell cocotb-config --makefiles)/Makefile.sim

Or pass WAVES=1 on the command line: make WAVES=1

For the more compact FST format, use COMPILE_ARGS += --trace-fst instead.

Waveform formats

--trace-vcd — Value Change Dump. Industry-standard, human-readable, larger files. Enabled by WAVES=1.
--trace-fst — Fast Signal Trace. Compressed binary format, much smaller files. Recommended for large designs.

View with GTKWave

After running make WAVES=1, open the generated waveform file:

gtkwave trace.vcd # or trace.fst if compiled with --trace-fst

Install GTKWave if you don't have it:

sudo apt install gtkwave