FFT forces program to wait until it's closed?


I created a very simple GRC graph with a sig_source, throttle and FFT
sink. Then I grafted the GUI code from the .py file so into the ieee
802.15.4 code on CGRAN so I can view the output that is going to the

It runs, but displays nothing and the program hangs until I close the
FFT window. After closing the FFT the program continues and loads the
packet into the msg_queue. There is a print statement so I know that
the wait/resume behavior is occurring.

I figure this is expected behavior and there is some simple usage
mistake on my part. Maybe the program needs to be rewritten in another
way to use the GUI components.

Here’s the original cgran code:


I had already replaced flow_graph with top_block and updated from
Numeric to NumPy. To make the GUI appear, I also had to replace
tb.start with tb.Run(True) and the class definition with:

class transmit_path(grc_wxgui.top_block_gui):
grc_wxgui.top_block_gui.init(self, title=“gui test”)

Any ideas?
Thanks for your help