UVM Agent

2023-12-04
#UVM #Testbench Structure
UVM

What is a UVM agent?

Agent將Sequencer、Driver和Monitor封裝到單一instance中，並透過TLM interface將這些component連接起來。Agent也有類似將UVM agent設定為主動(active)或被動(passive)的設置，也有類似開關的config可以開啟/關閉functional coverage或類似更改parameter的config。

Types of Agents

  • Active:
    • 會產生Sequencer, Driver, Monitor全部的instance
    • 會將data透過Driver驅動至DUT
  • Passive:
    • 只會產生Monitor的instance
    • 只有checking和coverage，並不會送任何資料到DUT
    • 如果沒有任何資料要驅動到DUT的話，可以用Passive mode

How to find out if a UVM agent is active or passive?

繼承uvm_agent的class會有一個get_is_active()的function可以得到UVM agent是Active mode還是Passive mode。

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class my_agent extends uvm_agent;
  virtual function void build_phase (uvm_phase phase);

    if (get_is_active()) begin
   // Build driver and sequencer
    end

    // Build monitor
  endfunction
endclass

Steps to create a UVM agent

  1. 建立一個繼承uvm_agent的class，然後註冊到factory上

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    class my_agent extends uvm_agent;

      `uvm_component_utils (my_agent)

      function new (string name = "my_agent", uvm_component parent = null);
        super.new (name, parent);
      endfunction

      ...
    endclass

  2. 宣告agent內要用的component

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    class my_agent extends uvm_agent;
      ...
      my_driver                  drv_0;
      my_monitor                 mon_0;
      uvm_sequencer #(my_data)   seqr_0;
      agent_cfg                  agt_cfg_0;
      ...
    endclass

  3. 在build phase將component實例化

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    class my_agent extends uvm_agent;
      ...
      virtual function void build_phase (uvm_phase phase);
        if (get_is_active()) begin
          m_seqr0 = uvm_sequencer#(my_data)::type_id::create ("m_seqr0", this);
          m_drv0 = my_driver::type_id::create ("m_drv0", this);
        end

        m_mon0 = my_monitor::type_id::create ("m_mon0", this);
      endfunction
      ...
    endclass

  4. 將agent元件連接在一起

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    class my_agent extends uvm_agent;
      virtual function void connect_phase (uvm_phase phase);

        if (get_is_active())
          m_drv0.seq_item_port.connect (m_seqr0.seq_item_export);
      endfunction
    endclass

What does a UVM agent do?

通常會建立一個agent來提供特定於protocol的task來產生transactions、檢查結果和執行覆蓋。例如，可以為 WishBone protocol建立 UVM agent，其sequencer將產生可傳送至driver的 data item。然後，driver將這些data item的object轉換為實際pin level的signal並將它們驅動到 DUT。monitor可以被動的只接收來自 DUT 的輸出，將它們轉換回另一個data item class object ，並將其分發到testbench中等待該data item的所有components中。

How to configure a UVM agent as active or passive?

A user-defined agent derived from uvm_agent has an internal variable called is_active which is of enum type uvm_active_passive_enum. By default, all agents are active.

從繼承uvm_agent自己定義的agent有一個 is_active 的變量，enum type為 uvm_active_passive_enum。default值為Active狀態。

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// set to passive
uvm_config_db #(int) :: set (this, "path_to_agent", "is_active", UVM_PASSIVE);
// or
// set to active
uvm_config_db #(int) :: set (this, "path_to_agent", "is_active", UVM_ACTIVE);