[Discuss-gnuradio] Re: Changing interp rate dynamically?

[Michael Dickens]

Revisiting this topic, since it's been 3 weeks and I've heard back  
nothing ... which probably means that everyone is too busy trying to  
get release 3.1 out the door to deal with this issue?  Should I just  
enter this as a bug to be fixed?

My original observation is that the USRP's TX interp rate doesn't  
seem to work when changed dynamically.  Brian and Eric and others  
replied back that the FPGA code looks OK, but that it's never really  
been tested for that purpose (the RX decim does work, and has been  
tested).  I have followed the TX path in software to the point where  
data is transferred to the USRP, and the data looks OK to that  
point.  It is possible that the USB transport is messing with the  
data, but I think that's unlikely.  It's much more likely that the  
FPGA code has a bug.  Unfortunately I do not "do" FPGA code yet,  
though I'm trying to learn, so I can't debug past where the data  
leaves the host computer.

Thus I created a -very- simple python script to test this issue.  My  
example code creates a sig_source with sinusoid and connects that to  
a USRP sink, set to 455 MHz at maximum gain and a given interp_rate.   
It starts the TB/FG running, then sleeps for 15 seconds.  It sets up  
a USRP for TX at a given interp_rate, then starts the FG running  
(which will be a separate thread) and sleeps for 15 seconds.  It then  
resets the interp_rate to -the same value-, and waits for the FG to  
finish (via user-interrupt).

I simultaneously run a waterfall scope on another computer, and can  
see the sinusoid as a "vertical line" on the scope (which is as  
expected).  After 15 seconds, the code sets the interp rate to the - 
same value- as before, and the waterfall scope changes  
dramatically ... most of the energy is "near" DC, but it looks  
somewhat like a time-sinusoid-modulated frequency-sinc.

Something is going on with the TX interp rate, most likely on the  
FPGA in my experimenting thus far (and/or: tell me what I'm doing  
incorrectly in my python script).  Please try out the example script,  
and see for yourselves. - MLD

test_usrp_interp.py
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