sv copy

1. 使用new操作符复制一个对象

class Header;
    int id;
    function new (int id);
        this.id = id;
    endfunction
    
    function showId();
        $display ("id=0x%0d", id);
    endfunction
endclass

class Packet;
    int     addr;
    int     data;
    Header     hdr;
    
    function new (int addr, int data, int id);
        hdr = new (id);
        this.addr = addr;
        this.data = data;
    endfunction
    
    function display (string name);
        $display ("[%s] addr=0x%0h data=0x%0h id=%0d", name, addr, data, hdr.id);
    endfunction
endclass

module tb;
    Packet p1, p2;
    initial begin
        // Create a new pkt object called p1
        p1 = new (32'hface_cafe, 32'h1234_5678, 26);
        p1.display ("p1");
        
        // Shallow copy p1 into p2; p2 is a new object with contents in p1
        p2 = new p1;
        p2.display ("p2");
        
        // Now let's change the addr and id in p1
        p1.addr = 32'habcd_ef12;
        p1.data = 32'h5a5a_5a5a;
        p1.hdr.id = 17;
        p1.display ("p1");
        
        // Print p2 and see that hdr.id points to the hdr in p1, while
        // addr and data remain unchanged.Shallow copy

 47 p2.display ("p2"); 48 end 49 endmodule

 这是一种简易复制（shallow copy），原对象的值被盲目copy到对象中，如果类A1中包含一个指向另一个子类B的句柄，那么复制类A2中只是复制了子类B的句柄，A1和A2中的B对象指向的是同一个对象。

2. 定义copy函数，实现深拷贝

class Header;
    int id;
    function new (int id);
        this.id = id;
    endfunction
    
    function showId();
        $display ("id=0x%0d", id);
    endfunction
endclass

class Packet;
    int     addr;
    int     data;
    Header     hdr;
    
    function new (int addr, int data, int id);
        hdr = new (id);
        this.addr = addr;
        this.data = data;
    endfunction
  
   function copy (Packet p);
      this.addr = p.addr;
      this.data = p.data;
      this.hdr.id = p.hdr.id;
   endfunction    
  
    function display (string name);
        $display ("[%s] addr=0x%0h data=0x%0h id=%0d", name, addr, data, hdr.id);
    endfunction
endclass

module tb;
    Packet p1, p2;
    initial begin
        p1 = new (32'hface_cafe, 32'h1234_5678, 32'h1a);
        p1.display ("p1");
        
        p2 = new (1,2,3);  // give some values
        p2.copy (p1);
        p2.display ("p2");
        
        // Now let's change the addr and id in p1
        p1.addr = 32'habcd_ef12;
        p1.data = 32'h5a5a_5a5a;
        p1.hdr.id = 32'h11;
        p1.display ("p1");
        
        // Now let's print p2 - you'll see the changes made to hdr id 
        // but not addr
        p2.display ("p2");
    end
endmodule

 3. copy 函数定义

// Code your testbench here
// or browse Examples
class base;
int p1;
  virtual function void copy(base orig);
    this.p1 = orig.p1;
  endfunction
  virtual function void display();
    $display("base:p1 = %d",this.p1);
  endfunction  
endclass
class ex_base extends base;
  int p2;
  virtual function void copy(base orig);
    super.copy(orig);
    this.p2 = p2;
  endfunction
  virtual function void display();
    $display("ex_base:p1 = %d, p2 = %d", this.p1, this.p2);
  endfunction    
endclass
 
module testbench();
base b1,b2;
ex_base eb1, eb2;
initial begin
   eb1 = new; eb2 = new();
   eb2.p2 = 5;
   b1 = eb1; b2 = eb2;
   b1.copy(b2); // p2 is not copied
   b1.display();
   b2.display();
   eb1.copy(eb2); // p2 is copied
   eb1.display();
   eb2.display();
end
endmodule

 

  4. do_copy

   virtual function void do_copy( uvm_object rhs ); //rhs 基类句柄
      jelly_bean_transaction that;//that 子类句柄 
 
      if ( ! $cast( that, rhs ) ) begin
         `uvm_error( get_name(), "rhs is not a jelly_bean_transaction" )
         return;
      end
 
      super.do_copy( rhs );
      this.flavor     = that.flavor;//前面通过$cast 进行向下类型转换，that 句柄成功的指向了rhs句柄指向的对象，然后进行赋值，达到copy的目的
      this.color      = that.color;
      this.sugar_free = that.sugar_free;
      this.sour       = that.sour;
      this.taste      = that.taste;
   endfunction: do_copy

  5. cast 的使用

将一个基类句柄tr 赋值给一个扩展类句柄ex_tr 并不总是合法的,当基类句柄tr指向的确实是扩展类ex_tr 的对象时，则是允许的。$cast 子程序会检查句柄所指向的对象的类型，而不仅仅是句柄类型。

$cast(ex_tr, tr) ;  检查tr句柄指向的对象的类型并拷贝句柄。（如果成功ex_tr 就指向tr 所指向的对象）

$cast(ex_tr, tr.clone()) ;  检查tr句柄指向的对象的类型并拷贝对象本身。