Pausing/restarting a sequence

Question

I have a design that requires a pause in data traffic to enter a low power mode. Is there a way to pause the traffic generation sequence or driver to allow this happen? And then resume the sequence at a later time?

I currently have a flag in the sequence that I set to tell it to break the forever loop. However, that is not ideal, because the sequence finishes and then I have to restart it.

Answer 1

You could lock (or grab the sequencer) from a virtual sequence, eg:

class virtual_seq extends uvm_sequence;

  `uvm_object_utils(virtual_zero_seq)
  `uvm_declare_p_sequencer(virtual_sequencer)

  function new(string name = "");
    super.new(name);
  endfunction: new

  task body;
    // start the normal traffic sequence
    normal_traffic_seq seq;
    seq = serial_fixed_seq::type_id::create("seq");
    if (! seq.randomize() ...
    seq.set_starting_phase(get_starting_phase());
    seq.start(p_sequencer.seqr, this);

    // when you're ready, lock the sequencer
    #12345;
    this.lock(p_sequencer.seqr);   // or grab

    // wait till you're ready to resume
    #12345; 
    // you could start another sequence on the same sequencer if you need to
    // if you do, you must input the reference to this virtual sequence in 
    // the sequence's start method, otherwise that sequence will be locked too
    // eg
    // power_down_seq.start(p_sequencer.seqr, this);
    //                                        ^^^^

    // when you're ready, start normal traffic again
    this.unlock(p_sequencer.seqr);   // or ungrab
  endtask : body

endclass : virtual_zero_seq

A grab is a higher priority lock. If multiple virtual sequences try to lock a sequencer, then they will gain access in the order they request it. If multiple virtual sequences try to grab a sequencer, if it is already locked (or grabbed), those virtual sequences will gain access to it on a last come first served basis.