How to execute "start_item()~finish_item()" when I use virtual sequence?

UVM
,
1

Dear All,

I’m trying to execute “start_item()~finish_item()” in a sequence. but problem is that
I’m stuck with error message [SEQ] neither the item’s sequencer nor dedicated sequencer has been supplied to start item when I start a virtual sequence with NULL.

Can’t I use “start_item()~finish_item()” in virtual sequence with NULL?
How to resolve sequence_item has null sequencer ?

class my_ahb extends my_base_test;

    `uvm_component_utils(my_ahb)
  
		my_ahb_base_test_seq_c my_ahb_base_test_seq;
		vseq_c	vseq;

    function new(string name = "my_ahb", uvm_component parent);
        super.new(name,parent);
    `uvm_info(get_type_name(), "Build my_ahb", UVM_NONE)
    endfunction : new

    function void build_phase(uvm_phase phase);
        super.build_phase(phase);

	my_ahb_base_test_seq = my_ahb_base_test_seq_c::type_id::create("my_ahb_base_test_seq");
	vseq = vseq_c::type_id::create("vseq");
    endfunction : build_phase

    task main_phase(uvm_phase phase);
        phase.raise_objection(this, "Test objection for main phase");
		vseq.my_ahb_seqr = systemTop_env0.my_ahb_agent0.m_sequencer;
//	Test Start.	
	
//////////////////////////////////////////////////////////////////////////////////////////////////////////
		my_ahb_base_test_seq.start(null); //<---This null makes Error, start_item() can't use null.
/////////////////////////////////////////////////////////////////////////////////////////////////////////

        phase.drop_objection(this, "Test objection for main phase");
    endtask : main_phase

endclass : my_ahb

------my_ahb_seq------------------

class my_ahb_seq_c extends uvm_sequence #(my_ahb_transaction);

 `uvm_object_utils_begin(my_ahb_seq_c)
//...
  `uvm_object_utils_end

  // new constructor  
  function new(string name="my_ahb_seq_c");
    super.new(name);
  endfunction // new

 
  virtual task body();
//...
  
	my_ahb_transaction tx;
	tx=my_ahb_transaction::type_id::create("tx");

	start_item(tx);
	tx.randomize();
    tx.start = m_start;
    finish_item(tx);

    get_response(rsp);

  endtask: body

endclass

and I was mas virtual sequence as the below

class vseq_c extends uvm_sequence;
	`uvm_object_utils (vseq_c)
	
my_ahb_seq_c	 my_ahb_seq;
my_ahb_sequencer my_ahb_seqr;

function new(string name="vseq_c");
	super.new(name);
  `uvm_info(get_type_name(), "the Virtual_sequence has been built", UVM_LOW)
endfunction

task pre_body();
my_ahb_seq		=	my_ahb_seq_c::type_id::create("my_ahb_seq");	
endtask

virtual task body();
fork begin
my_ahb_seq.start			(my_ahb_seqr);
end

join
endtask

endclass
2

In reply to UVM_LOVE:
I believe you have a wrong understanding of the virtual sequence. Such a sequence has 3 specific things:
(1) It does not create itself seq_items.
(2) It is used to orchstrate the local sequences.
(3) it is started in the test.

In your code it is unclear what you want to do.
You are starting an ahb sequence on the buck_seqr. But this sequences does not exist.
In your test you are starting my_ahb_base_test_seq_c on a null sequencer. But this seems to be a sequence which is a local sequences and has the intention to generate seq_items.

3

In reply to chr_sue:
Sorry for my typo I fix them.
But I am starting my_ahb_base_test_seq_c on a null sequencer. and that sequencer already connected as “vseq.my_ahb_seqr = systemTop_env0.my_ahb_agent0.m_sequencer;”.
my code no problem and work well if I removed start_item()~finish_item();
But I need start_item()~finish_item();

Could you guide me with little more code for correct?

4

In reply to UVM_LOVE:

Can you please share your code on EDAPlayground?