UVM Monitor

2023-12-01
#UVM #Testbench Structure
UVM

What is a monitor?

UVM monitor負責從design interface擷取訊號活動(activity)，並將其轉換為可傳送至其他component的data object。
為此，需要滿足以下條件：

  • 一個virtual interface handle，用於監視此monitor正在嘗試監視的實際interface。
  • 宣言一個TLM Analysis Port，用於向其他人廣播capture到的資料。

What does a UVM monitor do?

UVM monitorr繼承了uvm_monitor，具有以下功能：

  • 透過virtual interface收集bus或signal的資訊
  • 收集的數據可用於protocol檢查和覆蓋(coverage)
  • 透過analysis port將收集的數據匯出

UVM monitor的功能應該要盡量只有基本且一定需要的基本監控。它可能具有用於基本啟用/停用protocol的checking和coverage collection。比較high level的functional的checking應該要在scoreboard。

Steps to create a UVM monitor

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

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    class my_monitor extends uvm_monitor;

      `uvm_component_utils (my_monitor)

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

  2. 宣告analysis port和virtual interface handle

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    class my_monitor extends uvm_monitor;
      ...
      // Actual interface object is later obtained by doing a get() call on uvm_config_db
      virtual if_name vif;

      uvm_analysis_port  #(my_data) mon_analysis_port;
      ...
    endclass

  3. 建置UVM monitor，並在build phase建立analysis port的instance

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    class my_monitor extends uvm_monitor;
      ...
      virtual function void build_phase (uvm_phase phase);
        super.build_phase (phase);

        mon_analysis_port = new("mon_analysis_port", this);

        // Get virtual interface handle from the configuration DB
        if (! uvm_config_db #(virtual if_name)::get(this, "", "vif", vif)) begin
          `uvm_error (get_type_name (), "DUT interface not found")
        end
      endfunction
      ...
    endclass

  4. Code the run_phase

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    class my_monitor extends uvm_monitor;
      ...
      virtual task run_phase (uvm_phase phase);
        // Fork off multiple threads "if" required to monitor the interface, for example:
        fork
          // Thread 1: Monitor address channel
          // Thread 2: Monitor data channel, populate "obj" data object
          // Thread 3: Monitor control channel, decide if transaction is over

          // Thread 4: When data transfer is complete, send captured information
          // through the declared analysis port
          mon_analysis_port.write(obj);
        join_none
      endtask
      ...
    endclass