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

[Matt Ettus]

I think the problem is that the CIC interpolator needs to be stopped
before you change the rate.  It may also need to be reset, but I don't
think so.  I think the decimator had the same problem a while ago, and
it was fixed by stopping, changing the rate, and then restarting.  This
should be somewhere in the host code.

Matt

Michael Dickens wrote:
> 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
>
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