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 > > ------------------------------------------------------------------------ > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
