uvm_reg或uvm_reg_field的predict函数到底修改的什么值？desired value, or mirrored value?

答：desired value 和 mirrored value

 

// do_predict

function void uvm_reg_field::do_predict(uvm_reg_item      rw,
                                        uvm_predict_e     kind = UVM_PREDICT_DIRECT,
                                        uvm_reg_byte_en_t be = -1);
   
   uvm_reg_data_t field_val = rw.value[0] & ((1 << m_size)-1);

   if (rw.status != UVM_NOT_OK)
     rw.status = UVM_IS_OK;

   // Assume that the entire field is enabled
   if (!be[0])
     return;

   m_fname = rw.fname;
   m_lineno = rw.lineno;

   case (kind)

     UVM_PREDICT_WRITE:
       begin
         uvm_reg_field_cb_iter cbs = new(this);

         if (rw.path == UVM_FRONTDOOR || rw.path == UVM_PREDICT)
            field_val = XpredictX(m_mirrored, field_val, rw.map);

         m_written = 1;

         for (uvm_reg_cbs cb = cbs.first(); cb != null; cb = cbs.next())
            cb.post_predict(this, m_mirrored, field_val, 
                            UVM_PREDICT_WRITE, rw.path, rw.map);

         field_val &= ('b1 << m_size)-1;

       end

     UVM_PREDICT_READ:
       begin
         uvm_reg_field_cb_iter cbs = new(this);

         if (rw.path == UVM_FRONTDOOR || rw.path == UVM_PREDICT) begin

            string acc = get_access(rw.map);

            if (acc == "RC" ||
                acc == "WRC" ||
                acc == "WSRC" ||
                acc == "W1SRC" ||
                acc == "W0SRC")
              field_val = 0;  // (clear)

            else if (acc == "RS" ||
                     acc == "WRS" ||
                     acc == "WCRS" ||
                     acc == "W1CRS" ||
                     acc == "W0CRS")
              field_val = ('b1 << m_size)-1; // all 1's (set)

            else if (acc == "WO" ||
                     acc == "WOC" ||
                     acc == "WOS" ||
                     acc == "WO1" ||
                     acc == "NOACCESS")
              return;
         end

         for (uvm_reg_cbs cb = cbs.first(); cb != null; cb = cbs.next())
            cb.post_predict(this, m_mirrored, field_val,
                            UVM_PREDICT_READ, rw.path, rw.map);

         field_val &= ('b1 << m_size)-1;

       end

     UVM_PREDICT_DIRECT:
       begin
         if (m_parent.is_busy()) begin
           `uvm_warning("RegModel", {"Trying to predict value of field '",
              get_name(),"' while register '",m_parent.get_full_name(),
              "' is being accessed"})
           rw.status = UVM_NOT_OK;
         end
       end
   endcase

   // update the mirror with predicted value
   m_mirrored = field_val;
   m_desired  = field_val;
   this.value = field_val;

endfunction: do_predict