UVM Sequence

2023-11-29
#UVM #Testbench Structure
UVM

What is a UVM sequence?

UVM sequence由多個data item組成，這些data item可以以不同的方式組合在一起以創建出各種scenario。sequence會由指定的sequencer執行，然後sequencer將資料項傳送到driver。所以sequence是verification plan中的最主要的刺激(stimuli)。

Steps to create a UVM sequence

  1. 建立一個繼承uvm_sequence的class，然後註冊到factory上，因為uvm_sequence是繼承自uvm_transaction object，他的base其實是uvm_object，所以要使用uvm_object_utils而不是使用uvm_component_utils

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    // my_sequence is user-given name for this class that has been derived from "uvm_sequence"
    class my_sequence extends uvm_sequence;

      // `uvm_object_utils instead of `uvm_component_utils because sequence is a uvm_transaction object
      `uvm_object_utils (my_sequence)

      function new (string name = "my_sequence");
        super.new (name);
      endfunction
      ...
    endclass

  2. 宣告預設的sequencer來執行這個sequence

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    class my_sequence extends uvm_sequence;
      ...
      `uvm_declare_p_sequencer (my_sequencer)
      ...
    endclass

  3. 實作body method
    class my_sequence extends uvm_sequence;
    …
    virtual task body ();
    // Stimulus for this sequence
    endtask
    …
    endclass

UVM Sequence Example

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class my_sequence extends uvm_sequence;
  `uvm_object_utils (my_sequence)

  function new (string name = "my_sequence");
    super.new (name);
  endfunction

  task pre_body ();
	// ...
  endtask

  task body ();
    my_data pkt;
	`uvm_do (pkt);
  endtask

  task post_body();
    // ...
  endtask
endclass

NOTE:

  • my_sequence繼承了 uvm_sequence。
  • 它使用``uvm_object_utils向factory註冊，因為它是一個transaction item，transaction item是繼承uvm_object，而不是繼承uvm_component`。
  • 主要的stimulus是寫在body() task，而如果有需要在執行sequence之前或之後做什麼事情，可以call pre_body() 和 post_body() callback function
  • data packet建立好後由uvm_do macro傳送此data packet並執行

``uvm_domacro不會呼叫pre_body和post_body`。

``uvm_do` macro會allocate my_data類型的object給pkt，將它randomize然後傳送給此sequence關聯的sequencer然後將其執行。使用這個macro可以減少要寫的code。