The chip itself can only sample a single waveform, that must be done in the attached software. The current DRSOscilloscope software coming with the evaluation board has not yet implemented that, but if you write your own software you can do so.
I have a question about the function that drs4 can perform.
Is there any function in drs4 that is analogous to that of "persistence display" in oscilloscope?? (accumulating pulses)