The asix-sigma driver stalls the GUI when sigma_receive_data() determines that 
acquisition has or needs to be terminated, descends into download_capture(), 
and insists in retrieving all of the data in that very receive call, without 
returning to the main loop.  This gets worse with the slow USB transfer rate 
of the Sigma hardware and the huge sample memory of the device, which can 
result in several seconds of download time.

It's to get determined whether and how the sample download can get arranged 
such that USB communication can run in background and the GUI can process 
the data that was retrieved so far.