I can answer at least one of your questions. The tx_time tag is used for TDMA type applications where the burst *timing* is critical.
You send the burst a little in advance with the time tag, and the USRP won’t commence transmission until that time. Sent from my iPhone > On May 7, 2021, at 10:19 AM, Achilleas Anastasopoulos <[email protected]> > wrote: > > > I posted the following on discuss gnuradio list but I am also posting here in > case this is more appropriate. > --------------------------------------------------------- > Hi all, > > I am reading from here: > > https://wiki.gnuradio.org/index.php/USRP_Sink > > how to do burt transmission with the usrp_sink. > My questions have to do with the second option: > > ---- > Using tagged streams (See Tagged Stream Blocks). To use this capability, you > must specify which string the usrp_sink block should be looking for to denote > the length of the next PDU to be transmitted. Set the "tsb_tag_name" > parameter in the usrp_sink to whatever string your radio application uses to > denote your PDU length. A commonly used string for this purpose is simply > "tx_pkt_len". If using Tagged Streams for timed bursts, you must include your > "tx_pkt_len" tag and a "tx_time" tag on the first sample of a tx burst. If > your first "tx_pkt_len" tag has an offset of 0, and your packet length is > 1000 items, your next "tx_pkt_len" and "tx_time" tags must appear with an > offset of 1000. TX bursts should not overlap, and there should not be gaps in > samples between bursts. > ---- > > Q1: why do we need two tags to make this happen? I would think that > "tx_pkt_len" tag would be sufficient: when a tag like this is found by the > usrp sink then it waits for that many samples to come in and then it > transmits them in burst mode. Then it waits for the next such tag and so on. > What is the meaning/use of the second tag "tx_time"? > > Q2: Does the "tx_time" tag have to be exactly that name (as opposed to the > "tx_pkt_len" tag which can be user defined?) > > Q3: The text above is talking about PDU's but my understanding is that a PDU > is a special type of a PMT, while the USRP sink input has to be a tagged > stream, not a PMT/PDU. Should the input be a PDU (to a message port?) or > should it be a tagged stream? > > thanks > Achilleas > > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected]
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