Ian,
I also see those "S" errors, really strange. Initially, I thought that I might have screwed up the configuration somehow, as packetized MIMO operation seems to be a natural application for the B210. To circumvent the problem and in the hope that it might be fixed in a future release, I'm not using TSBs any more for now and just stream zeros, if need be, even though that is not really a satisfactory solution. Thanks for your time and looking into it! Cheers, Felix ________________________________ Von: Ian Buckley <ian.buck...@gmail.com> Gesendet: Freitag, 4. Mai 2018 06:12 An: Wunsch, Felix (CEL) Betreff: Re: [USRP-users] B210 dual channel operation with length tag in GNU Radio BTW, almost forgot to mention this to you. When I added the tagged stream blocks to my flow graph I reliably started to see two “S” errors indicated by UHD. I’m still scratching my head as to why there would be a deterministic sequence error indication…that seems very wrong to me, and not coincidental.Wish I had more free time to look at this for you, I’m curious. I also see a momentary RF transient preceding the case where both channels are disabled for the time offset we see. I can’t yet account for that, but it might be related to the differing latencies in the various paths that are changing state at the end of a transmission burst (These being internal TX state in the AD9361, external TX PA control , external TX/RX mux controls)….not clear if it’s some else that might be relevant. -Ian On May 3, 2018, at 4:38 AM, Wunsch, Felix (CEL) via USRP-users <usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com>> wrot Ian, thanks for the quick response! Actually, I'm not adding a tx_time tag. In my application, I want the packets to be transmitted simply as soon as possible and I was hoping that the two streamers of a single device were inherently synchronous. Comparing your flow graph to mine, I deactivated the "stream to tagged stream" blocks and set the master clock rate back to "Default" (previously, it was set to 16 MHz). It turns out that both settings independently seem to cause delays between my TX streams, i.e., without TSB tags and 16 MHz clock rate I see delays and also with TSB tags and a Default clock rate. Leaving out the TSBs and setting the Default clock rate, hence directly connecting the two vector sources to the UHD sink, results in the desired signal. But back to my original problem: Is there any way to get a synchronous dual-channel output for packetized samples that just sends as soon as possible? I have no problem with coding my own USRP sink block for this or a block that attaches SOB and EOB tags, I'd just like to avoid wasting time because I might trigger the same problem again. Also, I'd like to avoid getting the current time from the USRP each time I want to send a packet, if possible. By the way: Looking at the USRP sink implementation in gr-uhd, I can find only one call to get_tags_in_range and that one only looks at the first input, so I guess all other tags are ignored. Cheers, Felix ________________________________ Von: Ian Buckley <i...@ionconcepts.com<mailto:i...@ionconcepts.com>> Gesendet: Mittwoch, 2. Mai 2018 21:37 An: Wunsch, Felix (CEL) Cc: usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com> Betreff: Re: [USRP-users] B210 dual channel operation with length tag in GNU Radio Felix, Are you adding an explicit “tx_time” tag( with associated identical time tuple value) in both streams at the same offset as the TSB tag you are adding? I don’t think you can safely assume the TSB tag (Which causes bursting behavior in the USRP, equivalent to the use of the sob/eob) tags will cause both bursts to start at the same exact absolute time value. (Ready to be corrected by a GR guru on that….) Regardless attached is a simpler flow graph that uses streaming rather than bursting to achieve same effect you are looking for. The UHD sink guarantees to start two MIMO streams simultaneously for this kind of flow graph style. -Ian _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com<mailto:USRP-users@lists.ettus.com> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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