How to Use Virtual Sequencers to Control Both Non-virtual Sub Sequencers and Virtual Sub Sequencers

[Martin Borja]

Hello Everyone,

Good day.
I am creating a testbench that has a structure shown below and am encountering errors perhaps due to the multi-layered virtual sequencer controlling both non-virtual sub sequencers and a virtual sub sequencer. Config's not shown.
<start of diagram>
                       .------------------------------------------------------.
                       | my_test                                              |
                       | .--------------------------------------------------. |
                       | | sequences                                        | |
                       | '--------------------------------------------------' |
                       | .--------------------------------------------------. |
                       | | my_env                                           | |
                       | '--------------------------------------------------' |
                       '/----------------------------------------------------\'
                       /                                                      \
                      /                                                        \
                     /                                                          \
                    /                                                            \
                   /                                                              \
                  /                                                                \
                 /                                                                  \
                /                                                                    \
               /                                                                      \
              /                                                                        \
             /                                                                          \
            /                                                                            \
           /                                                                              \
          /                                                                                \
         /                                                                                  \
        /                                                                                    \
       /                                                                                      \
      /                                                                                        \
     /                                                                                          \
    /                                                                                            \
   /                                                                                              \
  /                                                                                                \
 /                                                                                                  \
.----------------------------------------------------------------------------------------------------.
| my_env                                                                                             |
|                                     .------------------------.                                     |
|                                     | my_virtual_sequencer   |                                     |
|                                     '------------------------'                                     |
| .-----------------------------------. .----------------------------. .---------------------------. |
| | sub_virtual_agent                 | | sub_agent_a                | | sub_agent_b               | |
| | .-------------------------------. | | .------------------------. | | .-----------------------. | |
| | | sub_virtual_sequencer         | | | | sub_sequencer_a        | | | | sub_sequencer_b       | | |
| | '-------------------------------' | | '------------------------' | | '-----------------------' | |
| |       .-------------------------. | | .------------------------. | | .-----------------------. | |
| |       | sub_agent_3             | | | | driver_a               | | | | driver_b              | | |
| |     .-------------------------. | | | '------------------------' | | '-----------------------' | |
| |     | sub_agent_2             | | | | .------------------------. | | .-----------------------. | |
| | .---------------------------. | | | | | monitor_a              | | | | monitor_b             | | |
| | | sub_agent_1               | | | | | '------------------------' | | '-----------------------' | |
| | | .-----------------------. | | | | '----------------------------' '---------------------------' |
| | | | sub_sequencer_1       | | | | |                                                              |
| | | '-----------------------' | | | |                                                              |
| | | .-----------------------. | | | |                                                              |
| | | | driver_1              | | | | |                                                              |
| | | '-----------------------' | | | |                                                              |
| | | .-----------------------. | | | |                                                              |
| | | | monitor_1             | | |-' |                                                              |
| | | '-----------------------' |-'   |                                                              |
| | '---------------------------'     |                                                              |
| '-----------------------------------'                                                              |
'----------------------------------------------------------------------------------------------------'
<end of diagram>

1) my_base_sequence (from w/c my_sequence_1 is extend)
<start snip>
class my_base_sequence extends uvm_sequence #(my_sequence_item);
  `uvm_object_utils(my_base_sequence)
  `uvm_declare_p_sequencer(sub_sequencer_1)
  function new (string name ="my_base_sequence");
    super.new(name);
  endfunction
  virtual task pre_start();
    if(get_parent_sequence() == null && starting_phase != null)
      starting_phase.raise_objection(get_sequencer());
    else
      `uvm_error(get_type_name(), "starting_phase is null")
  endtask
  virtual task post_start();
    if(get_parent_sequence() == null && starting_phase != null)
      starting_phase.drop_objection(get_sequencer());
  endtask
endclass
<end snip>

2) my_virtual_sequence
<start snip>
class my_virtual_sequence extends uvm_sequence;
  my_sequence_1 i_my_sequence_1;
  `uvm_object_utils(my_virtual_sequence)
  `uvm_declare_p_sequencer(my_virtual_sequencer)
  virtual task body();
    `uvm_do_on(i_my_sequence_1, p_sequencer.i_sub_virtual_sequencer.i_sub_sequencer_1);
  endtask
endclass
<end snip>

3) my_virtual_sequencer
<start snip>
class my_virtual_sequencer extends uvm_sequencer;
  sub_virtual_sequencer i_sub_virtual_sequencer;
  sub_sequencer_a       i_sub_sequencer_a;
  sub_sequencer_b       i_sub_sequencer_b;
  `uvm_component_utils(my_virtual_sequencer)
  function new (string name = "my_virtual_sequencer", uvm_component parent = null);
    super.new(name, parent);
  endfunction
  function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    i_sub_virtual_sequencer = sub_virtual_sequencer::type_id::create("i_sub_virtual_sequencer",this);
    i_sub_sequencer_a       = sub_sequencer_a::type_id::create("i_sub_sequencer_a",this);
    i_sub_sequencer_b       = sub_sequencer_b::type_id::create("i_sub_sequencer_b",this);
  endfunction
endclass
<end snip>

4) my_env
<start snip>
class my_env extends uvm_env;
  my_virtual_sequencer i_my_virtual_sequencer;
  sub_virtual_agent    i_sub_virtual_agent;
  sub_agent_a          i_sub_agent_a;
  sub_agent_b          i_sub_agent_b;
  `uvm_component_utils(my_env);
  extern function new (string name = "my_env", uvm_component parent = null);
  extern function void build_phase (uvm_phase phase);
  extern function void connect_phase (uvm_phase phase);
endclass
function my_env::new(string name = "my_env",uvm_component parent = null);
  super.new(name, parent);
endfunction
function void my_env::build_phase(uvm_phase phase);
  super.build_phase(phase);
  i_sub_virtual_agent = sub_virtual_agent::type_id::create("i_sub_virtual_agent",this);
  uvm_config_db #(uvm_object_wrapper)::set(this, "i_sub_virtual_agent.i_sub_virtual_sequencer.i_sub_sequencer_1.main_phase","default_sequence",null);
  uvm_config_db #(uvm_object_wrapper)::set(this, "i_sub_virtual_agent.i_sub_virtual_sequencer.i_sub_sequencer_2.main_phase","default_sequence",null);
  uvm_config_db #(uvm_object_wrapper)::set(this, "i_sub_agent_a.i_sub_sequencer_a.main_phase", "default_sequence",null);
  uvm_config_db #(uvm_object_wrapper)::set(this, "i_sub_agent_b.i_sub_sequencer_b.main_phase", "default_sequence",null);
endfunction
function void my_env::connect_phase(uvm_phase phase);
  super.connect_phase(phase);
  i_my_virtual_sequencer.i_sub_virtual_sequencer.i_sub_sequencer_1 = i_sub_virtual_agent.i_sub_virtual_sequencer.i_sub_sequencer_1;
  i_my_virtual_sequencer.i_sub_virtual_sequencer.i_sub_sequencer_2 = i_sub_virtual_agent.i_sub_virtual_sequencer.i_sub_sequencer_2;
  i_my_virtual_sequencer.i_sub_virtual_sequencer.i_sub_sequencer_3 = i_sub_virtual_agent.i_sub_virtual_sequencer.i_sub_sequencer_3;
  i_my_virtual_sequencer.i_sub_sequencer_a = i_sub_agent_a.i_sub_sequencer_a;
  i_my_virtual_sequencer.i_sub_sequencer_b = i_sub_agent_a.i_sub_sequencer_b;
endfunction
<end snip>

5) my_test
<start snip>
class my_test extends uvm_test;
  my_env i_my_env;
  `uvm_component_utils(my_test)
  extern function new (string name = "my_test",uvm_component parent = null);
  extern function void build_phase (uvm_phase phase);
endclass
function my_test::new(string name = "my_test", uvm_component parent = null);
  super.new(name, parent);
endfunction
function void my_test::build_phase(uvm_phase phase);
  super.build_phase(phase);
  i_my_env = my_env::type_id::create("i_my_env",this);
  uvm_config_db #(uvm_object_wrapper)::set(this, "i_my_env,i_my_virtual_sequencer.main_phase","default_sequence",my_virtual_sequence::type_id::get());
endfunction
<end snip>

The result of this test run is as follows:
<start snip>
UVM_ERROR /some_path/my_sequence_lib.sv(693) @400000 : uvm_test_top.i_my_env.i_sub_virtual_agent.i_sub_agent_1.i_sub_sequencer_1@@my_virtual_sequence.i_sub_sequence_1 [my_virtual_sequence] starting_phase is null
. . .
UVM_INFO /cad_tools_path/F-2011.12-SP1/etc/uvm/base/uvm_phase.svh(1233) @400000 : reporter [PH_READY_TO_END] Phase 'uvm.uvm_sched.main' (id=2956) PHASE READY TO END
<end snip>

And then it ended w/o running the sub_sequence_1.
The UVM_ERROR above shows that it was unable to get the raise.objection part to run.
Any help/inputs to this is much appreciated.

Thanks,

Martin