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Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?
From: |
Matt Ettus |
Subject: |
Re: [Discuss-gnuradio] Re: Changing interp rate dynamically? |
Date: |
Wed, 10 Oct 2007 11:49:11 -0700 |
User-agent: |
Thunderbird 2.0.0.0 (X11/20070326) |
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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- [Discuss-gnuradio] Re: Changing interp rate dynamically?, Michael Dickens, 2007/10/10
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?,
Matt Ettus <=
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Michael Dickens, 2007/10/10
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Matt Ettus, 2007/10/14
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Michael Dickens, 2007/10/15
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Matt Ettus, 2007/10/15
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Matt Ettus, 2007/10/15
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Michael Dickens, 2007/10/15
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Eric Blossom, 2007/10/15
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Michael Dickens, 2007/10/15
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Matt Ettus, 2007/10/16
- Re: [Discuss-gnuradio] Re: Changing interp rate dynamically?, Eric Blossom, 2007/10/15