UVM实战_1_UVM基础篇

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前言

本篇主要介绍UVM的几大组件，以及一些基础的知识

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一、继承uvm_component的几大组件

如上图，继承uvm_component的组件有uvm_agent/driver/monitor/scoreboard/env/test

1. uvm_driver

所有的driver都要派生自uvm_driver。driver的功能主要就是向sequencer索要sequence_item(transaction)，并且将sequence_item里的信息驱动到DUT的端口上，这相当于完成了从transaction级别到DUT能够接受的端口级别信息的转换。
相关代码如下：

class my_driver extends uvm_driver#(my_transaction);
   virtual my_if vif;
   `uvm_component_utils(my_driver)//加入factory机制，把my_driver注册在UVM内部的一张表中
   function new(string name = "my_driver", uvm_component parent = null);//每一个派生自uvm_component在new函数中都要指明两个参数：name和parent
      super.new(name, parent);
   endfunction

   virtual function void build_phase(uvm_phase phase);
      super.build_phase(phase);
      if(!uvm_config_db#(virtual my_if)::get(this, "", "vif", vif))
         `uvm_fatal("my_driver", "virtual interface must be set for vif!!!")
   endfunction

   extern task main_phase(uvm_phase phase);//driver所做的事情几乎都在main_phase中完成
   extern task drive_one_pkt(my_transaction tr);
endclass

task my_driver::main_phase(uvm_phase phase);
   vif.data <= 8'b0;
   vif.valid <= 1'b0;
   while(!vif.rst_n)
      @(posedge vif.clk);
   while(1) begin
      seq_item_port.get_next_item(req);//得到一个新的req，并且驱动它
      drive_one_pkt(req);
      seq_item_port.item_done();//驱动完req后，通知sequencer
   end
endtask

2. uvm_monitor

所有的monitor都要派生自uvm_monitor。monitor做的事情与driver相反，driver向DUT的pin上发送数据，而monitor则是从DUT的pin上接收数据，并且把接收到的数据转换成transaction级别的sequence_item，再把转换后的数据发送给scoreboard或者reference model，供其比较。

class my_monitor extends uvm_monitor;
   virtual my_if vif;
   uvm_analysis_port #(my_transaction)  ap;
   `uvm_component_utils(my_monitor)
   
   function new(string name = "my_monitor", uvm_component parent = null);
      super.new(name, parent);
   endfunction
   
   virtual function void build_phase(uvm_phase phase);
      super.build_phase(phase);
      if(!uvm_config_db#(virtual my_if)::get(this, "", "vif", vif))
         `uvm_fatal("my_monitor", "virtual interface must be set for vif!!!")
      ap = new("ap", this);
   endfunction

   extern task main_phase(uvm_phase phase);
   extern task collect_one_pkt(my_transaction tr);
endclass

task my_monitor::main_phase(uvm_phase phase);
   my_transaction tr;
   while(1) begin
      tr = new("tr");
      collect_one_pkt(tr);
      ap.write(tr);
   end
endtask

DUT的输入口设置一个monitor有必要吗？
第一，在一个大型的项目中，driver根据某一协议发送数据，而monitor根据这种协议收集数据，如果driver和monitor由不同的人员实现，那么可以大大减少其中任何一方对协议理解的错误；
第二，在实现代码重用时，使用monitor是非常有必要的。

3. uvm_sequencer

所有的sequencer都要派生自uvm_sequencer。sequencer的功能就是组织管理sequence，当driver要求数据时，它就把sequence生成的sequence_item转发给driver。

class my_sequencer extends uvm_sequencer #(my_transaction);
   
   function new(string name, uvm_component parent);
      super.new(name, parent);
   endfunction 
   
   `uvm_component_utils(my_sequencer)
endclass

4. uvm_scoreboard

一般的scoreboard都派生自uvm_scoreboard。scoreboard的功能就是比较reference model和monitor分别发送来的数据，根据比较结果判断DUT是否正确工作。

class my_scoreboard extends uvm_scoreboard;
   my_transaction  expect_queue[$];
   uvm_blocking_get_port #(my_transaction)  exp_port;
   uvm_blocking_get_port #(my_transaction)  act_port;
   `uvm_component_utils(my_scoreboard)

   extern function new(string name, uvm_component parent = null);
   extern virtual function void build_phase(uvm_phase phase);
   extern virtual task main_phase(uvm_phase phase);
endclass 

function my_scoreboard::new(string name, uvm_component parent = null);
   super.new(name, parent);
endfunction 

function void my_scoreboard::build_phase(uvm_phase phase);
   super.build_phase(phase);
   exp_port = new("exp_port", this);
   act_port = new("act_port", this);
endfunction 

task my_scoreboard::main_phase(uvm_phase phase);
   my_transaction  get_expect,  get_actual, tmp_tran;
   bit result;
   bit cmp_en = 1'b1;
 
   super.main_phase(phase);
   fork
      while(1) begin
         uvm_config_db#(bit)::wait_modified(this, "", "cmp_en");//这里是什么意思？后续在看
         void'(uvm_config_db#(bit)::get(this, "", "cmp_en", cmp_en)); 
         `uvm_info("my_scoreboard", $sformatf("cmp_en value modified, the new value is %0d", cmp_en), UVM_LOW)
      end
      while (1) begin
         exp_port.get(get_expect);
         expect_queue.push_back(get_expect);
      end
      while (1) begin
         act_port.get(get_actual);
         if(expect_queue.size() > 0) begin
            tmp_tran = expect_queue.pop_front();
            result = get_actual.compare(tmp_tran);
            if(result) begin 
               `uvm_info("my_scoreboard", "Compare SUCCESSFULLY", UVM_LOW);
            end
            else begin
               `uvm_error("my_scoreboard", "Compare FAILED");
               $display("the expect pkt is");
               tmp_tran.print()