Verilator介绍

Verilator是一种开源的Verilog/SystemVerilog仿真器，可用于编译代码以及代码在线检查，Verilator能够读取Verilog或者SystemVerilog文件，并进行lint checks(基于lint工具的语法检测)，并最终将其转换成C++的源文件.cpp和.h。

Verilator不直接将Verilog HDL转换为C++或者SystemC，反之Verilator将代码编译成更快的优化过的并且支持多线程的模型，该模型被依次包装在（wrapped）在C++/SystemC模型中。这样就生成一个编译的Verilog模型，其功能和Verilog是一致的，但效率由于基于C++即使是单线程模型也可以10倍快于SystemC，100倍快于基于解释Verilog的仿真器，并且通过多线程可以进一步加速。

Verilator的优点：将Verilog/SystemVerilog转换成C++/SystemC，仿真速度快很多，如果有这方面的需求，那Verilator是不错的选择。

本节将先介绍下Verilator的安装以及基本的使用方法，所有操作均在Ubuntu16系统上实现。

Verilator安装

安装必要的软件包：

sudo apt-get install git perl python3 make autoconf g++ flex bison ccache
sudo apt-get install libgoogle-perftools-dev numactl perl-doc
sudo apt-get install libfl-dev
sudo apt-get install zlibc zlib1g zlib1g-dev

git上拷贝源代码：

git clone https://github.com/verilator/verilator

编译前的准备工作：

unset VERILATOR_ROOT  # For bash
cd verilator
git pull         # Make sure git repository is up-to-date
git tag          # See what versions exist

这里选择编译版本v4.210(最新版本会报错)

git checkout v4.210 

配置编译安装：

autoconf         # Create ./configure script
./configure      # Configure and create Makefile
make -j `nproc`  # Build Verilator itself (if error, try just 'make')
sudo make install

如果成功的话输入：

verilator --version

可以看到verilator的版本信息：

一个简单例子

下面我们看下官方示例，最简单的hello world代码，文件位置在verilator/examples/make_hello_c/下，主要两个文件：

top.v

// DESCRIPTION: Verilator: Verilog example module
//
// This file ONLY is placed under the Creative Commons Public Domain, for
// any use, without warranty, 2017 by Wilson Snyder.
// SPDX-License-Identifier: CC0-1.0

// See also the EXAMPLE section in the verilator manpage/document.
module top;
   initial begin
      $display("Hello World!");
      $finish;
   end
endmodule

sim_main.cpp

// DESCRIPTION: Verilator: Verilog example module
//
// This file ONLY is placed under the Creative Commons Public Domain, for
// any use, without warranty, 2017 by Wilson Snyder.
// SPDX-License-Identifier: CC0-1.0
//======================================================================

// Include common routines
#include <verilated.h>

// Include model header, generated from Verilating "top.v"
#include "Vtop.h"

int main(int argc, char** argv, char** env) {
    // See a similar example walkthrough in the verilator manpage.

    // This is intended to be a minimal example.  Before copying this to start a
    // real project, it is better to start with a more complete example,
    // e.g. examples/c_tracing.

    // Prevent unused variable warnings
    if (false && argc && argv && env) {}

    // Construct the Verilated model, from Vtop.h generated from Verilating "top.v"
    Vtop* top = new Vtop;

    // Simulate until $finish
    while (!Verilated::gotFinish()) {

        // Evaluate model
        top->eval();
    }

    // Final model cleanup
    top->final();

    // Destroy model
    delete top;

    // Return good completion status
    return 0;
}

MakeFile文件：

######################################################################
#
# DESCRIPTION: Verilator Example: Small Makefile
#
# This calls the object directory makefile.  That allows the objects to
# be placed in the "current directory" which simplifies the Makefile.
#
# This file ONLY is placed under the Creative Commons Public Domain, for
# any use, without warranty, 2020 by Wilson Snyder.
# SPDX-License-Identifier: CC0-1.0
#
######################################################################
# Check for sanity to avoid later confusion

ifneq ($(words $(CURDIR)),1)
 $(error Unsupported: GNU Make cannot build in directories containing spaces, build elsewhere: '$(CURDIR)')
endif

######################################################################

# This is intended to be a minimal example.  Before copying this to start a
# real project, it is better to start with a more complete example,
# e.g. examples/make_tracing_c.

# If $VERILATOR_ROOT isn't in the environment, we assume it is part of a
# package install, and verilator is in your path. Otherwise find the
# binary relative to $VERILATOR_ROOT (such as when inside the git sources).
ifeq ($(VERILATOR_ROOT),)
VERILATOR = verilator
else
export VERILATOR_ROOT
VERILATOR = $(VERILATOR_ROOT)/bin/verilator
endif

default:
	@echo "-- Verilator hello-world simple example"
	@echo "-- VERILATE & BUILD --------"
	$(VERILATOR) -cc --exe --build -j top.v sim_main.cpp
	@echo "-- RUN ---------------------"
	obj_dir/Vtop
	@echo "-- DONE --------------------"
	@echo "Note: Once this example is understood, see examples/make_tracing_c."
	@echo "Note: Also see the EXAMPLE section in the verilator manpage/document."

######################################################################

maintainer-copy::
clean mostlyclean distclean maintainer-clean::
	-rm -rf obj_dir *.log *.dmp *.vpd core

MakeFile中核心的编译语句其实就是执行：

verilator -Wall --cc --exe --build top.v sim_main.cpp

直接执行编译：

make

执行生成的C++可执行文件，结果如下：

可以看到C++实现了和verilog相同的功能。

配合gtkwave实现波形仿真

安装gtkwave

gtkwave同样是开源的工具其git地址为：

https://github.com/gtkwave/gtkwave.git

这里我们直接安装：

sudo apt-get install gtkwave

简单示例

以一个简单的逻辑组合为例：

top.v

module top(
  input a,
  input b,
  input c,
  input d,
  output f
);
  assign f = ~((a&b) | (~(c&d)));
endmodule

top_main.cpp

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
 
#include "Vtop.h"  // create `top.v`,so use `Vtop.h`
#include "verilated.h"
 
#include "verilated_vcd_c.h" //可选，如果要导出vcd则需要加上
 
int main(int argc, char** argv, char** env) {
 
  VerilatedContext* contextp = new VerilatedContext;
  contextp->commandArgs(argc, argv);
  Vtop* top = new Vtop{contextp};
  
 
  VerilatedVcdC* tfp = new VerilatedVcdC; //初始化VCD对象指针
  contextp->traceEverOn(true); //打开追踪功能
  top->trace(tfp, 0); //
  tfp->open("wave.vcd"); //设置输出的文件wave.vcd
 
 
  while (!contextp->gotFinish()) {
    int a = rand() & 1;
    int b = rand() & 1;
    int c = rand() & 1;
    int d = rand() & 1;
    top->a = a;
    top->b = b;
    top->c = c;
    top->d = d;
    top->eval();
    printf("a = %d, b = %d, c = %d, d = %d, f = %d\n", a, b, c, d, top->f);
 
    tfp->dump(contextp->time()); //dump wave
    contextp->timeInc(1); //推动仿真时间
 
    assert(top->f == ~((a&b) | (~(c&d))));
  }
  delete top;
  tfp->close();
  delete contextp;
  return 0;
}

执行编译：

verilator -Wall top.v top_main.cpp --cc --trace --exe --build
#增加了--trace 是为了显示波形的
./obj_dir/Vtop   //必须执行这个，才会出现.vcd文件，需要强制退出
gtkwave wave.vcd //如果报错缺少canberra-gtk-module，apt安装即可

结果如下图：

 这一节先说到这里。