这是寄存器模型类中唯一派生自uvm_component的类，我们的寄存器模式需要实时，以最接近的方式知道DUT中寄存器的变化，uvm_reg_predictor就是为这个而生的。

// TITLE: Explicit Register Predictor
//------------------------------------------------------------------------------
//
// The <uvm_reg_predictor> class defines a predictor component,
// which is used to update the register model's mirror values
// based on transactions explicitly observed on a physical bus. 
//------------------------------------------------------------------------------

class uvm_predict_s;
   bit addr[uvm_reg_addr_t];
   uvm_reg_item reg_item;
endclass

//------------------------------------------------------------------------------
//
// CLASS: uvm_reg_predictor
//
// Updates the register model mirror based on observed bus transactions
//
// This class converts observed bus transactions of type ~BUSTYPE~ to generic
// registers transactions, determines the register being accessed based on the
// bus address, then updates the register's mirror value with the observed bus
// data, subject to the register's access mode. See <uvm_reg::predict> for details.
//
// Memories can be large, so their accesses are not predicted.
//
//------------------------------------------------------------------------------

class uvm_reg_predictor #(type BUSTYPE=int) extends uvm_component;

  `uvm_component_param_utils(uvm_reg_predictor#(BUSTYPE))

  // Variable: bus_in
  //
  // Observed bus transactions of type ~BUSTYPE~ are received from this
  // port and processed.
  //
  // For each incoming transaction, the predictor will attempt to get the
  // register or memory handle corresponding to the observed bus address. 
  //
  // If there is a match, the predictor calls the register or memory's
  // predict method, passing in the observed bus data. The register or
  // memory mirror will be updated with this data, subject to its configured
  // access behavior--RW, RO, WO, etc. The predictor will also convert the
  // bus transaction to a generic <uvm_reg_item> and send it out the
  // ~reg_ap~ analysis port.
  //
  // If the register is wider than the bus, the
  // predictor will collect the multiple bus transactions needed to
  // determine the value being read or written.
  //
  uvm_analysis_imp #(BUSTYPE, uvm_reg_predictor #(BUSTYPE)) bus_in;


  // Variable: reg_ap
  //
  // Analysis output port that publishes <uvm_reg_item> transactions
  // converted from bus transactions received on ~bus_in~.
  uvm_analysis_port #(uvm_reg_item) reg_ap;


  // Variable: map
  //
  // The map used to convert a bus address to the corresponding register
  // or memory handle. Must be configured before the run phase.
  // 
  uvm_reg_map map;


  // Variable: adapter
  //
  // The adapter used to convey the parameters of a bus operation in 
  // terms of a canonical <uvm_reg_bus_op> datum.
  // The <uvm_reg_adapter> must be configured before the run phase.
  //
  uvm_reg_adapter adapter;


  // Function: new
  //
  // Create a new instance of this type, giving it the optional ~name~
  // and ~parent~.
  //
  function new (string name, uvm_component parent);
  endfunction

  // This method is documented in uvm_object
  static string type_name = "";
  virtual function string get_type_name();
  endfunction
  
  // Function: pre_predict
  //
  // Override this method to change the value or re-direct the
  // target register
  //
  virtual function void pre_predict(uvm_reg_item rw);
  endfunction

  local uvm_predict_s m_pending[uvm_reg];


  // Function- write
  //
  // not a user-level method. Do not call directly. See documentation
  // for the ~bus_in~ member.
  //
  virtual function void write(BUSTYPE tr);
  endfunction

  
  // Function: check_phase
  //
  // Checks that no pending register transactions are still queued.

  virtual function void check_phase(uvm_phase phase);
  endfunction

endclass