uvm sequencer和driver通信

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uvm driver从sequencer FIFO中获取request类型的sequence item（REQ）， 类似握手协议， 返回一个response类型的（RSP）。如下图所示：

本篇主要介绍在driver中使用get_next_item的方法。

这种情况下， driver获取sequence item主要是通过seq_item_port, 比如下面的代码：

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class my_driver extends uvm_driver #(my_data);
  `uvm_component_utils (my_driver)
 
   virtual task run_phase(uvm_phase phase);
      super.run_phase(phase);
 
      // 1. This task will get an item from the sequencer using get_next_item()
      `uvm_info ("DRIVER", $sformatf ("Waiting for data from sequencer"), UVM_MEDIUM)
      seq_item_port.get_next_item(req);
 
      // 2. For simplicity, lets just assume the driver drives the received packet
      // during this time and consumes 20ns to complete driving the transaction
      `uvm_info ("DRIVER", $sformatf ("Start driving tx addr=0x%0h data=0x%0h", req.addr, req.data), UVM_MEDIUM)
      #20;
 
      // 3. After driver has finished the transaction, it has to let the sequencer know
      // by calling item_done()
      `uvm_info ("DRIVER", $sformatf ("Finish driving tx addr=0x%0h data=0x%0h", req.addr, req.data), UVM_MEDIUM)
      seq_item_port.item_done();
   endtask

一旦driver完成驱动interface上的信号， 就可以用item_done的方法通知sequencer。

那么sequencer又是如何获取sequence item的呢？

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class my_sequence extends uvm_sequence;
  `uvm_object_utils (my_sequence)
 
 
  virtual task body();
    // 1. Create an item the connected sequencer can accept
    my_data tx = my_data::type_id::create("tx");
    `uvm_info ("SEQ", $sformatf("About to call start_item"), UVM_MEDIUM)
 
    // 2. Call the start_item() task which will send this object to the driver
    start_item(tx);
    `uvm_info ("SEQ", $sformatf("start_item() fn call done"), UVM_MEDIUM)
 
    // 3. Because the class handle passed to the driver points to the same object, we 
    // can do late randomization
    tx.randomize();
    `uvm_info ("SEQ", $sformatf("tx randomized with addr=0x%0h data=0x%0h", tx.addr, tx.data), UVM_MEDIUM)
 
    // 4. Call finish_item method so that the sequence waits until the driver lets the 
    // sequencer know that this item has finished
    finish_item(tx);
    `uvm_info ("SEQ", $sformatf("finish_item() fn call done"), UVM_MEDIUM)
  endtask
endclass