In reply to bmorris:
If you have to consider a register value you can access this register through the register layer. It’s very simple and powerful.
I don’t understand what you mean with layered agents. You might have layered sequences, i.e a high lever sequnence which is passing high level data to a low level sequence. This works also fine without haveing any time-dependency. If the driver has to wait for any reason no additional seq_item (high and low level) will be generated until the current item has been completed.