How to Control a Multi-layered Agent's Sub Sequencer Using a Top Level Virtual Sequencer

[Martin Borja]

Hello Everyone,

I am trying to control a sub virtual sequencer's non-virtual sub sequencers using a top level virtual sequencer.
It looks like this diagram.

<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>

I am trying to apply section 4.8 Virtual Sequences of uvm users guide.
But I think I am missing on something.

I have a top level virtual sequence that has the top level virtual sequencer as its p_sequencer. I have this in the macro:

`uvm_declare_p_sequencer(my_virtual_sequencer)

And then I have this in the task body() to access the sub sequencer of the sub virtual sequencer:

`uvm_do_on(sub_sequence_1, p_sequencer.i_sub_virtual_sequencer.i_sub_sequencer_1);

sub_sequence_1 is a physical sequence.
Is this correct under the UVM standard?
If not, how do I properly control i_sub_sequencer_1?

This is how I access it in the test build_phase:

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());

Any help/inputs to this is much appreciated.

Thanks,
Martin

[bhunter1972]

Looks pretty good to me, so long as my_virtual_sequencer has a handle to the sub_virtual_sequencers, and these must have handles to their respective sub_sequencers. You can do this either through the config_db, or just by assignment during the connect phase.

 

Also, your setting of the default sequence has a comma where there should be a period, after i_my_env.

 

Nice pic, btw.

[Martin Borja]

Hi bhunter1972,

 

 

Thanks for your input.

Regarding the comma in:

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());

It is a typographical error, my bad.

 

When running the code, I see the top virtual sequence, virtual sub sequence and physical sequence start (based on uvm_infos printed out).

The problem though happens once inside main_phase.

The simulation halts with messages saying there is no default sequence (tool is VCS synopsys) as if the default_sequence was not set as in the above quote.

 

I also checked the handles and they are very much complete per hierarchy.

 

Any light into this is much appreciated.

 

Thanks,

Martin

[bhunter1972]

The simulation halts with messages saying there is no default sequence (tool is VCS synopsys) as if the default_sequence was not set as in the above quote.

 

Well, that is strange. I can certainly imagine that with string matching being as error-prone as it may be that you might not have a match. But the simulation halting because of no default sequence is not typical behavior.

 

The two things that I can think of are:

1. Run with +UVM_CONFIG_DB_TRACE on the command-line. More 'stuff' will be sent to the screen/logfile to tell you if your default sequence config matched up or not.
2. Does your virtual sequence raise/drop the objection? If it doesn't--and if nobody else does--the main phase can certainly complete in zero time and your sequence gets garbage-collected away, having accomplished nothing.

Your sequence should have something like this in it:

 

if(starting_phase) 
   starting_phase.raise_objection(); 
...

...
if(starting_phase)
   starting_phase.drop_objection();

[Martin Borja]

Thank you for your response.

It is #2 that's happening.

I have a raise and drop objection in the physical sequence's pre_start() and post_start() tasks and the

 

if(starting_phase != null)

 

condition fails so

 

starting_phase.raise_objection(get_sequencer());

 

does not happen.

What happens after is main ends right away.

 

Am I correct in placing the raise_objection and drop_objection in the physical sequence?

If so, how come it does not satisfy starting_phase != null when the code is running?

 

Thanks,

Martin

[bhunter1972]

A sequence only has the 'starting_phase' field set when it is set as the default_sequence for a sequencer's phase.  It is seen as the "top" sequence in that case.  

 

So, in your case it's the "my_virtual_sequence" instance that must raise the objection.

 

However--and I think this is important--you should put that code in all of your virtual sequences.  Because someday, your "my_virtual_sequence" may be called upon by another virtual sequence, and it won't be the one raising an objection.