Here we use iVerilog+GTKWave for simulation by default, and VCS+Verdi are also supported in simulation environment, you can choose the simulation tool by Makefile variable SIM. If you want to run simulation tests directly, please make sure these EDA tools are installed in your working environment.
make clean
make install
make compile SIM=iverlog or make compile SIM=VCS
make run_test SIM=iverilog or make run_test SIM=vcs
make wave SIM=iverilog or make wave SIM=vcs
If you use iVerilog as simulation tool, please make sure the tool verison is 12.0.