uvm_sequence_item——sequence机制（一）

让子弹飞一会

　　UVM框架，将验证平台和激励分开，env以下属于平台部分，test和sequence属于激励，这样各司其职。我们可以将sequence_item 比喻成子弹，sequencer 类比成弹夹，UVM平台就是个枪。如图所示uvm_sequence 的类继承关系。

The sequence item is written by extending the uvm_sequence_item, uvm_sequence_item inherits from the uvm_object via the uvm_transaction class.

//------------------------------------------------------------------------------
//
// CLASS: uvm_sequence_item
//
// The base class for user-defined sequence items and also the base class for
// the uvm_sequence class. The uvm_sequence_item class provides the basic
// functionality for objects, both sequence items and sequences, to operate in
// the sequence mechanism.
//
//------------------------------------------------------------------------------

class uvm_sequence_item extends uvm_transaction;

  local      int                m_sequence_id = -;
  protected  bit                m_use_sequence_info;
  protected  int                m_depth = -;
  protected  uvm_sequencer_base m_sequencer;
  protected  uvm_sequence_base  m_parent_sequence;
  static     bit issued1,issued2;
  bit        print_sequence_info;

  // Function: new
  //
  // The constructor method for uvm_sequence_item. 

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

  function string get_type_name();
    return "uvm_sequence_item";
  endfunction 

  // Macro for factory creation
  `uvm_object_registry(uvm_sequence_item, "uvm_sequence_item")

   ......
endclass

参考文献：

1 SequenceR and SequenceS. http://www.chipverify.com/uvm/sequencer-and-sequences

2 UVM Sequence item & Methods. http://www.verificationguide.com/p/uvm-sequence-item.html