uvm_transaction——事物

文件：

src/base/uvm_transaction.svh

类: 

uvm_transaction

 

　　uvm_transaction继承自uvm_object,添加了timing和recording接口，该类是uvm_sequence_item的基类。这个类提供了时间戳属性(timestamp properties),通知事件(notification events),和交易记录(transaction recording)支持。其子类uvm_sequence_item应当作为基类为所有用户定义的事务类型。

//------------------------------------------------------------------------------
//
// CLASS: uvm_transaction
//
// The uvm_transaction class is the root base class for UVM transactions.
// Inheriting all the methods of <uvm_object>, uvm_transaction adds a timing and
// recording interface.
//
// This class provides timestamp properties, notification events, and transaction
// recording support. 
//
// Use of this class as a base for user-defined transactions
// is deprecated. Its subtype, <uvm_sequence_item>, shall be used as the
// base class for all user-defined transaction types. 
// 
// The intended use of this API is via a <uvm_driver #(REQ,RSP)> to call <uvm_component::accept_tr>,
// <uvm_component::begin_tr>, and <uvm_component::end_tr> during the course of
// sequence item execution. These methods in the component base class will
// call into the corresponding methods in this class to set the corresponding
// timestamps (~accept_time~, ~begin_time~, and ~end_time~), trigger the
// corresponding event (<begin_event> and <end_event>, and, if enabled,
// record the transaction contents to a vendor-specific transaction database.
//
// Note that get_next_item/item_done when called on a uvm_seq_item_pull_port
// will automatically trigger the begin_event and end_events via calls to begin_tr and end_tr.
// While convenient, it is generally the responsibility of drivers to mark a
// transaction's progress during execution.  To allow the driver or layering sequence
// to control sequence item timestamps, events, and recording, you must call
// <uvm_sqr_if_base#(REQ,RSP)::disable_auto_item_recording> at the beginning
// of the driver's ~run_phase~ task.
//
// Users may also use the transaction's event pool, <events>,
// to define custom events for the driver to trigger and the sequences to wait on. Any
// in-between events such as marking the beginning of the address and data
// phases of transaction execution could be implemented via the
// <events> pool.
// 
// In pipelined protocols, the driver may release a sequence (return from
// finish_item() or it's `uvm_do macro) before the item has been completed.
// If the driver uses the begin_tr/end_tr API in uvm_component, the sequence can
// wait on the item's <end_event> to block until the item was fully executed,
// as in the following example.
//
//| task uvm_execute(item, ...);
//|     // can use the `uvm_do macros as well
//|     start_item(item);
//|     item.randomize();
//|     finish_item(item);
//|     item.end_event.wait_on();
//|     // get_response(rsp, item.get_transaction_id()); //if needed
//| endtask
//|
//
// A simple two-stage pipeline driver that can execute address and
// data phases concurrently might be implemented as follows: 
//
//| task run();
//|     // this driver supports a two-deep pipeline
//|     fork
//|       do_item();
//|       do_item();
//|     join
//| endtask
//| 
//| 
//| task do_item();
//|     
//|   forever begin
//|     mbus_item req;
//|
//|     lock.get();
//|
//|     seq_item_port.get(req); // Completes the sequencer-driver handshake
//|
//|     accept_tr(req);
//|
//|       // request bus, wait for grant, etc.
//| 
//|     begin_tr(req);
//|
//|       // execute address phase
//|
//|     // allows next transaction to begin address phase
//|     lock.put();
//| 
//|       // execute data phase
//|       // (may trigger custom "data_phase" event here)
//| 
//|     end_tr(req);
//| 
//|   end
//| 
//| endtask: do_item
//
//------------------------------------------------------------------------------
virtual class uvm_transaction extends uvm_object;

  // Function: new
  //
  // Creates a new transaction object. The name is the instance name of the
  // transaction. If not supplied, then the object is unnamed.
  
  extern function new (string name="", uvm_component initiator=null);

   ......

endclass

参考文献：

1 uvm_transaction. http://blog.sina.com.cn/s/blog_466496f30100y7u9.html

2 UVM基础之———uvm_transaction. http://www.cnblogs.com/bob62/p/3871858.html