[UVM] copy object

UVM has provided field automation mechanism, UVM can use built-in functions, such as print, clone, copy ...., today to talk about my problems with the copy function.

class cfg1 extends uvm_object;

  int id;
  
  ....
endclass

===============================================================

class cfg2 extends uvm_object;

  int id;
  cfg1 sub_cfg;

  function new(string name = "cfg");
    super.new(name);
    sub_cfg = cfg1::type_id::create("sub_cfg");
  endfunction
  
endclass

===============================================================

class ref extends uvm_component;
   ...
    cfg2 o_cfg;
    cfg1 s_cfg;

   virtual function void build_phase(uvm_phase phase)
     super.build_phase(phase);
     if(!uvm_config_db#(cfg2)::get(this,$sformatf("o_cfg2"),"cfg",o_cfg))
       `uvm_fatal(...)

     s_cfg = o_cfg.sub_cfg;//保存了sub_cfg的handle
     
   endfunction
endclass

The class cfg2 embodiment comprises a variable int and a cfg1 the object, if the updated CFG2 run_phase copy function call:

o_cfg_ary = cfg2::type_id::create("o_cfg_ary");
o_cfg_ary.sub_cfg.id = 2;
o_cfg.copy(o_cfg_ary);

 After o_cfg update, ref still get the original value! ! ! !

---

root cause：

copy function is a deep copy , so the object cfg2 in the copying sub_cfg reallocate memory space, i.e., handle address changes.

PS: Copy function copies only use field automation registered variables and Object .

In general build_phase using Config_db transfer handle , once passed on, if the middle handle changes, in above example would want to use copy function change ID (guaranteed handle address change, only update content) , but o_cfg .sub_cfg the handle address generating change, and the ref holds sub_cfg handle the address resulting in the need to obtain handle of the class get to the handle is still pointing to the original memory space .

1. If the ref is employed by sub_cfg o_cfg.sub_cfg.id, copy function does not influence (even o_cfg.sub_cfg the handle does not affect the change of the address );

2. If the ref in "s_cfg = o_cfg.sub_cfg" saved sub_cfg handle the address , but o_cfg.sub_cfg the handle address changes, sub_cfg can not point to the newly allocated space, will not get the value after the update;

solution：

o_cfg_ary = cfg2::type_id::create("o_cfg_ary");
o_cfg_ary.sub_cfg.id = 2;
o_cfg.copy(o_cfg_ary);
o_cfg.sub_cfg.copy(o_cfg_ary.sub_cfg);//递归调用copy函数