how to start virtual sequencer ?

A virtual sequencer is a sequencer that can run sequences, but it doesn’t connect to any drivers,hence the virtual name. It is designed to run virtual sequences that spawn sub-sequences on other sequencers.

1 You can start virtual sequences on a virtual sequencer.

2 Handles part of the virtual sequence  can be started on null virtual sequencer , it means you can start() the virtual sequence on a ‘null’ virtual sequencer.

Example 

1 virtual Sequence is started on the Virtual Sequencer

For example

task run_phase (uvm_phase phase);
/// Create the Virtual Sequence
my_vseq vsequence = my_vseq::type_id::create(“vseq”);
phase.raise_objection(this);
/// Virtual Sequence Initialization
init_vseq(vsequence );
/// Start the Virtual Sequence
vsequence.start(null);
phase.drop_objection(this);
endtask: run_phase
>vsequence is virtual sequence , v_sqr is handle of virtual sequencer , vseq is started on v_sqr

2 Sequence is started on null sequencer

For example

task run_phase (uvm_phase phase);
/// Create the Virtual Sequence
my_vseq vsequence = my_vseq::type_id::create(“vsequence “);
phase.raise_objection(this);
/// Virtual Sequence Initialization
init_vsequence (vsequence);
/// Start the Virtual Sequence
vsequence.start(null);
phase.drop_objection(this);
endtask: run_phase
> my_vseq is a  virtual sequence , inside init_vseq is function which has connection of   the sequencer handles to the handles in virtual sequence class

>vsequence.start(null) is way to start virtual sequence