What is virtual sequencer ? when and how to use it ?

Virtual sequencer : it contains handles of the sequencer which are located in different agent

Q. Question is when do we use it ??

Why do use it

if something has to be synchronized , in general stimulus generation across different interface has to be synchronized, which is done by Virtual sequencer , virtual sequences

in practical if you have two ip on soc and you want to have stimulus control , virtual sequencer , virtual sequences helps to you achieve it

How do we use it

consider seqr1 , seqr2 are handles of sequencers ,also they belongs to two agent seq1_agent, seq2_agent, and have env as envionemnt

Lets see how to use it ??

Define Virtual sequence

///// Virtual Sequencer Class

1. class virtual_seqr extend uvm_sequencer;
2. `uvm_component_utils(virtual_seqr)
4. /// Handles of different sequencer
5. type1_seqr seqr1;
6. type2_seqr seqr2;
8. /// Constructor
9. function new (string name = “virtual_seqr”, uvm_component parent);
10. super.new(name, parent);
11. endfunction: new
13. endclass: virtual_seqr

Now if we go further

how virtual sequencer is instantiated in virtual sequence

for that lets define base sequence class

1. ///// Virtual Sequence Class
2. class virtual_base_seq extend uvm_sequence #(uvm_sequence_item) ;
3. `uvm_component_utils(virtual_base_seq )
5. type1_seqr seqr_b1;
6. type2_seqr seqr_b2;
7. // Virtual sequencer handle
8. virtual_seqr v_seqr;
10. /// Constructor
11. function new (string name = “virtual_base_seq”);
12. super.new(name);
13. endfunction: new
14. task body ();
15. if (!$cast(v_seqr, m_sequencer)) begin
16. `uvm_error(get_full_name(), “Virtual Seqr pointer cast failed”)
17. end
18. seqr_b1= v_seqr.seqr1;
19. seqr_b2= v_seqr.seqr2;
21. endtask: body
23. endclass: virtual_base_seq

Now lets lets define virtual sequence

1. class virtual_seq extend virtual_base_seq ;
2. `uvm_component_utils(virtual_seq )
4. type1_seqr seqr_b1;
5. type2_seqr seqr_b2;
6. // Virtual sequencer handle
7. virtual_seqr v_seqr;
9. /// Constructor
10. function new (string name = “virtual_seq”);
11. super.new(name, parent);
12. endfunction: new
13.  
14. task body ();
15. // call parent file to assign sub sequence handles
16. super.body();
17. type1_seq seq1;
18. type2_seq seq2;
19. //create seq
20. seq1= type1_seq::type_id::create(“type1_seq “);
21. seq2= type1_seq::type_id::create(“type1_seq “);
22. repeat (10) begin
23. seq1.start();
24. seq2.start();
25. end
26. endtask: body
28. endclass: virtual_base_seq

Environment will instantiate virtual sequencer , agent and make connection to virtual sequencer to agent sequencer

not going in details it’s connect phase will be like

1. function void connect_phase (uvm_phase phase);
2. v_seqr.seqr1 = seg1_agent.m_sequencer;
3. v_seqr.seqr2 = seq2_agent.m_sequencer;
4. endfunction: connect_phase

also test will instantiate virtual sequence , environment

and its run phase will be like

1. task run_phase (uvm_phase phase);
2. /// Create the Virtual Sequence
3. v_seq_test = virtual_seq::type_id::create(“v_seq_test”);
4. phase.raise_objection(this);
5. /// Start the Virtual Sequence
6. v_seq_test.start(env.v_seqr_env);
7. phase.drop_objection(this);
8. endtask: run_phase