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> Gesendet: Mittwoch, 2. Mai 2018 21:37 An: Wunsch, Felix (CEL) Cc: 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
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