13.3 Start a sequence

1.?How to start a sequence?

通过调用start方法启动sequence，该方法接受指向sequencer的指针，sequence_item通过该sequencer发送给driveer。sequencer的指针也通常称为m_sequencer。start方法为m_sequencer分配一个sequencer指针，然后调用body()任务。完成与driver交互的主体任务后，start()方法返回。由于它需要与driver交互，因此start()是一种阻塞方法。

2. start method definition

virtual task start ( uvm_sequencer_base sequencer,
                     uvm_sequence_base parent_sequence = null,
                     int this_priority = -1;
                     bit call_pre_post = 1;

对于名为child_seq的sequence，可以如下所示调用start方法：?

assert(child_seq.randomize());
child_seq.start(seqr, parent_seq, priority, call_pre_post);

在sequence执行期间，通过start方法调用以下方法：

?

注：

1. mid_do和post_do是函数，其他方法是任务。
2. 始终调用pre_start和post_start方法。

start方法调用遵循以下顺序：

sub_seq.pre_start()        
sub_seq.pre_body()          if call_pre_post==1 
  parent_seq.pre_do(0)      if parent_sequence!=null 
  parent_seq.mid_do(this)   if parent_sequence!=null
sub_seq.body                YOUR STIMULUS CODE 
  parent_seq.post_do(this)  if parent_sequence!=null 
sub_seq.post_body()         if call_pre_post==1 
sub_seq.post_start()

为了清楚地理解它，base_seq及其派生序列child_seq是用定义的所有方法编写的。

下面仅显示base_seq和child_seq序列。完整的代码可以在可执行链接中找到。?

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 pre_start();
    `uvm_info(get_type_name(), "Base seq: Inside pre_start", UVM_LOW);
  endtask
  
  task pre_body();
    `uvm_info(get_type_name(), "Base seq: Inside pre_body", UVM_LOW);
  endtask
  
  virtual task pre_do(bit is_item);
    `uvm_info(get_type_name(), "Base seq: Inside pre_do", UVM_LOW);
  endtask
  
  virtual function void mid_do(uvm_sequence_item this_item);
    `uvm_info(get_type_name(), "Base seq: Inside mid_do", UVM_LOW);
  endfunction
  
  task body();
    `uvm_info(get_type_name(), "Base seq: Inside Body", UVM_LOW);
    `uvm_do(req); // Calls all pre_do, mid_do and post_do methos.
    /*
    req = seq_item::type_id::create("req");
    wait_for_grant();
    assert(req.randomize());
    send_request(req);
    wait_for_item_done(); */
  endtask
  
  virtual function void post_do(uvm_sequence_item this_item);
    `uvm_info(get_type_name(), "Base seq: Inside post_do", UVM_LOW);
  endfunction
  
  task post_body();
    `uvm_info(get_type_name(), "Base seq: Inside post_body", UVM_LOW);
  endtask
endclass

class child_seq extends base_seq;
  `uvm_object_utils(child_seq)
  
  function new (string name = "child_seq");
    super.new(name);
  endfunction

  task pre_start();
    `uvm_info(get_type_name(), "Child seq: Inside pre_start", UVM_LOW);
  endtask
  
  task pre_body();
    `uvm_info(get_type_name(), "Child seq: Inside pre_body", UVM_LOW);
  endtask
  
  task pre_do(bit is_item);
    `uvm_info(get_type_name(), "Child seq: Inside pre_do", UVM_LOW);
  endtask
  
  function void mid_do(uvm_sequence_item this_item);
    `uvm_info(get_type_name(), "Child seq: Inside mid_do", UVM_LOW);
  endfunction
  
  task body();
    `uvm_info(get_type_name(), "Child seq: Inside Body", UVM_LOW);
     //`uvm_do(req); // Calls all pre_do, mid_do and post_do methos.
    
    /*req = seq_item::type_id::create("req");
    wait_for_grant();
    assert(req.randomize());
    send_request(req);
    wait_for_item_done();*/
    
    req = seq_item::type_id::create("req");
    start_item(req);
    assert(req.randomize());
    finish_item(req);
  endtask
  
  function void post_do(uvm_sequence_item this_item);
    `uvm_info(get_type_name(), "Child seq: Inside post_do", UVM_LOW);
  endfunction
  
  task post_body();
    `uvm_info(get_type_name(), "Child seq: Inside post_body", UVM_LOW);
  endtask
endclass

输出：

UVM_INFO testbench.sv(19) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside pre_start
UVM_INFO testbench.sv(23) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside pre_body
UVM_INFO testbench.sv(35) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside Body
UVM_INFO testbench.sv(27) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside pre_do
UVM_INFO testbench.sv(31) @ 0: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside mid_do
UVM_INFO driver.sv(16) @ 0: uvm_test_top.env_o.agt.drv [driver] Driving logic
UVM_INFO testbench.sv(46) @ 50: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside post_do
UVM_INFO testbench.sv(50) @ 50: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside post_body
-----------------------------------------------------------------------------------
UVM_INFO testbench.sv(62) @ 50: uvm_test_top.env_o.agt.seqr@@cseq [child_seq] Child seq: Inside pre_start
UVM_INFO testbench.sv(66) @ 50: uvm_test_top.env_o.agt.seqr@@cseq [child_seq] Child seq: Inside pre_body
UVM_INFO testbench.sv(78) @ 50: uvm_test_top.env_o.agt.seqr@@cseq [child_seq] Child seq: Inside Body
UVM_INFO testbench.sv(70) @ 50: uvm_test_top.env_o.agt.seqr@@cseq [child_seq] Child seq: Inside pre_do
UVM_INFO testbench.sv(74) @ 50: uvm_test_top.env_o.agt.seqr@@cseq [child_seq] Child seq: Inside mid_do
UVM_INFO driver.sv(16) @ 50: uvm_test_top.env_o.agt.drv [driver] Driving logic
UVM_INFO testbench.sv(94) @ 100: uvm_test_top.env_o.agt.seqr@@cseq [child_seq] Child seq: Inside post_do
UVM_INFO testbench.sv(98) @ 100: uvm_test_top.env_o.agt.seqr@@cseq [child_seq] Child seq: Inside post_body
-----------------------------------------------------------------------------------
UVM_INFO testbench.sv(62) @ 100: uvm_test_top.env_o.agt.seqr@@bseq.cseq [child_seq] Child seq: Inside pre_start
UVM_INFO testbench.sv(66) @ 100: uvm_test_top.env_o.agt.seqr@@bseq.cseq [child_seq] Child seq: Inside pre_body
UVM_INFO testbench.sv(27) @ 100: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside pre_do
UVM_INFO testbench.sv(31) @ 100: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside mid_do
UVM_INFO testbench.sv(78) @ 100: uvm_test_top.env_o.agt.seqr@@bseq.cseq [child_seq] Child seq: Inside Body
UVM_INFO testbench.sv(70) @ 100: uvm_test_top.env_o.agt.seqr@@bseq.cseq [child_seq] Child seq: Inside pre_do
UVM_INFO testbench.sv(74) @ 100: uvm_test_top.env_o.agt.seqr@@bseq.cseq [child_seq] Child seq: Inside mid_do
UVM_INFO driver.sv(16) @ 100: uvm_test_top.env_o.agt.drv [driver] Driving logic
UVM_INFO testbench.sv(94) @ 150: uvm_test_top.env_o.agt.seqr@@bseq.cseq [child_seq] Child seq: Inside post_do
UVM_INFO testbench.sv(46) @ 150: uvm_test_top.env_o.agt.seqr@@bseq [base_seq] Base seq: Inside post_do
UVM_INFO testbench.sv(98) @ 150: uvm_test_top.env_o.agt.seqr@@bseq.cseq [child_seq] Child seq: Inside post_body