15 Sequence-Driver-Sequencer communication in UVM

我们分别讨论了sequece_item、sequence、sequencer和driver。在本节中，我们将讨论他们如何相互talk，sequencer如何给driver提供从sequence里的sequence item。在开始阅读本节之前，请确保您了解sequencer和driver中使用的所有方法。（参考：UVM seqeuencer和UVM driver ). 

1 Sequencer-Driver Connections

sequencer和driver使用双向TLM接口相互通信，以传输REQ和RSP序列项。

driver的uvm_seq_iem_pull _port和相应的sequencer的uvm_seq_item_pull_export连接。这个TLM接口提供了一个工具，可以使用实现的API检索REQ item并返回RSP项。
注：

1. uvm_seq_item_pull_port和uvm_secq_itemp_pull_export都是带有REQ和RSP sequence item的参数化类。
2. driver和sequencer之间的TLM连接是一对一的。这意味着没有多个sequencer连接到单个driver，也没有多个driver连接到单个sequencer。

connections：driver和sequence在UVM agent的connect_phase中连接。

.seq_item_port.connect(.seq_item_export);

seq_item_port和seq_iem_export分别是uvm_seq_itemp_pull_port和uvm_sseq_tem_pull_export的实例句柄(instance handle)。 

2 Sequence-Driver-Sequencer communication Approaches

基于sequence和driver可用的各种方法，进一步解释所有组合。

方法A：Using get_next_item and item_done methods in the driver

方法B：Using get and put methods in driver

2.1 A. Using get_next_item and item_done methods in the driver

2.1.1 Without RSP packet

1. 创建一个sequence item，并使用create_item函数在工厂中注册。
2. wait_for_grant向sequencer发出请求，并等待sequencer的授权。当sequencer授予sequence时返回。
3. 对sequence item进行随机化，并使用send_request将其发送到sequencer。wait_for_grant和send_request方法之间不能有任何仿真时间延迟。sequencer在REQ FIFO的帮助下将sequence item转发给driver。这将取消阻止get_next_item()调用，driver将接收序列sequence item。
4. 来自sequence的wait_for_item_done()调用被阻止，直到driver响应。
5. 同时，driver使用virtual interface句柄将sequence item驱动到DUT。完成后，将调用item_done方法。这将从sequence中取消阻止wait_for_item_done方法。
6. 如果必须从driver向sequence发送响应，则使用RSP项作为参数调用item_done(RSP)。RSP项目通过sequencer在RSP FIFO的帮助下与sequence通信。调用get_response方法以获取响应很重要。如果DUT没有发送RSP项目，则此步骤是可选的，不是必需的。 

// Driver Code
class driver extends uvm_driver#(seq_item);
  `uvm_component_utils(driver)
  
  function new(string name = "driver", uvm_component parent = null);
    super.new(name, parent);
  endfunction
  
  function void build_phase(uvm_phase phase);
    super.build_phase(phase);
  endfunction
  
  task run_phase (uvm_phase phase);
    forever begin
      seq_item_port.get_next_item(req);
      `uvm_info(get_type_name(), "After get_next_item call", UVM_LOW);
      #50; // Driving delay. Assuming time taken to drive RTL signals
      seq_item_port.item_done();
      `uvm_info(get_type_name(), "After item_done call", UVM_LOW);
    end
  endtask
endclass

// Sequence Code
class base_seq extends uvm_sequence #(seq_item);
  seq_item req;
  `uvm_object_utils(base_seq)
  
  function new (string name = "base_seq");
    super.new(name);
  endfunction

  task body();
    `uvm_info(get_type_name(), "Base seq: Inside Body", UVM_LOW);
    //req = seq_item::type_id::create("req");
    // or
    $cast(req, create_item(seq_item::get_type(), m_sequencer, "req"));
    wait_for_grant();
    assert(req.randomize());
    send_request(req);
    `uvm_info(get_type_name(), "Before wait_for_item_done", UVM_LOW);
    wait_for_item_done();
    `uvm_info(get_type_name(), "After wait_for_item_done", UVM_LOW);
  endtask
endclass

Output:

UVM_INFO testbench.sv(21) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside Body
UVM_INFO testbench.sv(28) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Before wait_for_item_done
UVM_INFO driver.sv(15) @ 0: uvm_test_top.env_o.agt.drv [driver] After get_next_item call
UVM_INFO driver.sv(19) @ 50: uvm_test_top.env_o.agt.drv [driver] After item_done call
UVM_INFO testbench.sv(30) @ 50: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] After wait_for_item_done

2.1.2 With RSP packet

// Driver Code
class driver extends uvm_driver#(seq_item);
  `uvm_component_utils(driver)
  
  function new(string name = "driver", uvm_component parent = null);
    super.new(name, parent);
  endfunction
  
  function void build_phase(uvm_phase phase);
    super.build_phase(phase);
  endfunction
  
  task run_phase (uvm_phase phase);
    forever begin
      seq_item_port.get_next_item(req);
      `uvm_info(get_type_name(), "After get_next_item call", UVM_LOW);
      #50; // Driving delay. Assuming time taken to drive RTL signals
      req.rsp_b = 1;
      seq_item_port.item_done(req);
      `uvm_info(get_type_name(), "After item_done call", UVM_LOW);
    end
  endtask
endclass

// Sequence Code
class base_seq extends uvm_sequence #(seq_item);
  seq_item req;
  `uvm_object_utils(base_seq)
  
  function new (string name = "base_seq");
    super.new(name);
  endfunction

  task body();
    `uvm_info(get_type_name(), "Base seq: Inside Body", UVM_LOW);
    //req = seq_item::type_id::create("req");
    // or
    $cast(req, create_item(seq_item::get_type(), m_sequencer, "req"));
    wait_for_grant();
    assert(req.randomize());
    send_request(req);
    `uvm_info(get_type_name(), "Before wait_for_item_done", UVM_LOW);
    wait_for_item_done();
    `uvm_info(get_type_name(), "After wait_for_item_done", UVM_LOW);
    get_response(req);
    `uvm_info(get_type_name(), $sformatf("After get_response: rsp_b = %0d", req.rsp_b), UVM_LOW);
  endtask
endclass

 Output:

UVM_INFO testbench.sv(21) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside Body
UVM_INFO testbench.sv(28) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Before wait_for_item_done
UVM_INFO driver.sv(15) @ 0: uvm_test_top.env_o.agt.drv [driver] After get_next_item call
UVM_INFO driver.sv(20) @ 50: uvm_test_top.env_o.agt.drv [driver] After item_done call
UVM_INFO testbench.sv(30) @ 50: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] After wait_for_item_done
UVM_INFO testbench.sv(32) @ 50: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] After get_response: rsp_b = 1

2.2 B. Using get and put methods in driver

1. Create a sequence item and register in the factory using the create_item function call.
2. The wait_for_grant issues the request to the sequencer and wait for the grant from the sequencer. It returns when the sequencer has granted the sequence.
3. Randomize the sequence item and send it to the sequencer using send_request call. There should not be any simulation time delay between wait_for_grant and send_request method call. The sequencer forwards the sequence item to the driver with the help of REQ FIFO. This unblocks the get() call and the driver receives the sequence item.
4. The wait_for_item_done() call from the sequence gets blocked until the driver calls the get method.
5. Once the get method is called, the wait_for_item_done() call from sequence gets unblocked immediately without caring about driving the virtual interface.
6. The get_response call is necessary to call that completes the communication. The get_response method is blocked until the driver calls put(RSP).
7. In the meantime, the driver drives the sequence item to the DUT using a virtual interface handle. Once it is completed, the put(RSP) method is called. This unblocks the get_response method from the sequence. The RSP item is communicated to the sequence by a sequencer with help of RSP FIFO. 

// Driver Code
class driver extends uvm_driver#(seq_item);
  `uvm_component_utils(driver)
  
  function new(string name = "driver", uvm_component parent = null);
    super.new(name, parent);
  endfunction
  
  function void build_phase(uvm_phase phase);
    super.build_phase(phase);
  endfunction
  
  task run_phase (uvm_phase phase);
    forever begin
      seq_item_port.get(req);
      `uvm_info(get_type_name(), "After get call", UVM_LOW);
      #50; // Driving delay. Assuming time taken to drive RTL signals
      req.rsp_b = 1;
      seq_item_port.put(req);
      `uvm_info(get_type_name(), "After put call", UVM_LOW);
    end
  endtask
endclass

// Sequence Code
class base_seq extends uvm_sequence #(seq_item);
  seq_item req;
  `uvm_object_utils(base_seq)
  
  function new (string name = "base_seq");
    super.new(name);
  endfunction

  task body();
    `uvm_info(get_type_name(), "Base seq: Inside Body", UVM_LOW);
    //req = seq_item::type_id::create("req");
    // or
    $cast(req, create_item(seq_item::get_type(), m_sequencer, "req"));
    wait_for_grant();
    assert(req.randomize());
    send_request(req);
    `uvm_info(get_type_name(), "Before wait_for_item_done call", UVM_LOW);
    wait_for_item_done();
    `uvm_info(get_type_name(), "After wait_for_item_done call", UVM_LOW);
    get_response(req);
    `uvm_info(get_type_name(), $sformatf("After get_response: rsp_b = %0d", req.rsp_b), UVM_LOW);
  endtask
endclass

Output:

UVM_INFO testbench.sv(21) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside Body
UVM_INFO testbench.sv(28) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Before wait_for_item_done call
UVM_INFO driver.sv(15) @ 0: uvm_test_top.env_o.agt.drv [driver] After get call
UVM_INFO testbench.sv(30) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] After wait_for_item_done call
UVM_INFO driver.sv(20) @ 50: uvm_test_top.env_o.agt.drv [driver] After put call
UVM_INFO testbench.sv(32) @ 50: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] After get_response: rsp_b = 1