Efficient Sequence Objection in UVM

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Objections are handled in pre/post body decalared in a base sequence class

This is efficient for all sequence execution options:

  • Default sequences use body objections

  • Test sequences use test objections

  • Subsequences use objections of the root sequence which calls them

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class yapp_base_seq extends uvm_sequence#(yapp_packet);
…
    task pre_body();
        if(starting_phase != null);
        	starting_phase.raise_objection(this, get_type_name());
    endtask
    task post_body();
    	if(starting_phase != null);
    		starting_phase.drop_objection(this, get_type_name());	
    endtask
…
class yapp012 extends yapp_base_seq;
…

Set as default sequence of sequencer:

A default sequence is a root sequence, so the pre/post body methods are executed and objection are raised/dropped there

Test sequence:

A test sequence is a root sequence, so the pre/post body methods are executed. However, for a test sequence, starting_phase is null and so the objection is not handled in the sequence. The test must raise and drop objections

Subsequence:

Not a root sequence, so pre/post body methods are not executed. The root sequence which ultimately called the subsequence handles the objections, using one of the two options above.

If a sequence is call via a `uvm_do variant, the it is defined as a subsequence and its pre/post_body() methods are not executed.

objection change in UVM1.2

Raising or dropping objections directly from starting_phase is deprecated

  • must use get_starting_phase() method

  • prevents modification of phase during sequence

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task pre_body();
    uvm_phase sp = get_starting_phase();
    if (sp != null)
        sp.raise_objection(this, get_type_name());
endtask