You see "L" because you are sending your bursts far enough advance
should have read: "aren't sending your bursts far enough in advance" On Mon, Jun 3, 2013 at 5:59 PM, John Malsbury <john.malsb...@ettus.com>wrote: > " It'll switch to TX when it receives samples to send." > > There may be some small [intentional] delays, but the FPGA will switch to > Tx on the first sample to be sent. Josh can specify the timing in more > detail. > > You see "L" because you are sending your bursts far enough advance. In my > applications, the bursts are sent to the USRP about ~5ms before the actual > transmission. And as far as I know you can't just use the fractional > seconds. The FPGA won't switch to TX when it hits tx_time and starts clock > out the samples. > > -John > > > On Mon, Jun 3, 2013 at 4:59 PM, Miklos Maroti <mmar...@math.u-szeged.hu>wrote: > >> Hi John, >> >> Thanks for you quick reply, but you did not answer any of my >> questions. Will the FPGA switch from TX to RX when it has already >> received from the host a UDP packet with a timestamp tag (tx_time) >> that is in the future? Also, when exactly will the RX to TX switch >> occur? >> >> Miklos >> >> On Mon, Jun 3, 2013 at 6:14 PM, John Malsbury <john.malsb...@ettus.com> >> wrote: >> > If you choose TX/RX as both your transmit and receive antenna, the FPGA >> will >> > switch between TX and RX automatically. It'll switch to TX when it >> receives >> > samples to send. >> > >> > -John >> > >> > >> > On Mon, Jun 3, 2013 at 3:33 PM, Miklos Maroti <mmar...@gmail.com> >> wrote: >> >> >> >> Hi Guys! >> >> >> >> I am trying to develop a half duplex application with N210 and SBX >> >> daughterboard with the latest (git head) gnuradio that needs precise >> >> TX/RX switching times (like in TDMA) in the order of a few samples >> >> (nanoseconds). I have played with the tx_time, tx_sob, tx_eob tags and >> >> they do not seem to solve the problem. My findings so far are: >> >> >> >> 1) tx_sob/tx_eob does not influence anything related to the TX/RX >> >> switch, it only controls the grouping of the TX data stream into UDP >> >> packets (tx_sob starts a new UDP packet, tx_eof pushes out the last >> >> UDP packet even if it is not full). The same is true for USRP1 but >> >> that uses USB packets. >> >> >> >> 2) tx_time is translated into the metadata_t struct in the host code >> >> and then it is translated into VITA packet time stamps (converts the >> >> fractional second part into sample numbers). The integer part of >> >> tx_time seems to be discarded, but I still get "L" (timestamp in the >> >> past error), so I do not understand why the FPGA will not wait a >> >> little if only the factional part is considered. >> >> >> >> 3) I have found this discussion online about TX/RX switch: >> >> >> >> >> http://lists.gnu.org/archive/html/discuss-gnuradio/2009-03/msg00034.html >> >> >> >> where Matt Ettus said that "The act of transmitting turns off the >> >> receiver, so no amount of software will ever change that." in >> >> discussing half duplex operation. Now it is not clear if that comment >> >> is also applicable to the N210 and SBX, and what does he mean by "the >> >> act of transmitting". Specifically, if I send a packet with tx_time in >> >> the future, does the FPGA switches to RX mode while it is waiting? >> >> >> >> 4) We have looked up the FPGA code, and it seems that the timing is >> >> implemented in a short FIFO when handling the VITA UDP packets. I >> >> could not trace the code further, and I do not see the logic in the >> >> FPGA code that does the automatic switching between RX and TX. Where >> >> is that implemented? >> >> >> >> 5) Is it true that to switch between RX and TX then the host has to >> >> issue a command (poke register) to update the appropriate pin on the >> >> FPGA? If so, then how can you time the update of that pin to specific >> >> sample numbers? >> >> >> >> 6) Is it true that the firmware soft core has nothing to do with the >> >> time sensitive data and control handling, so in particular the >> >> provided register access features (if I saw them correctly) are not >> >> used in timing sensitive paths? >> >> >> >> 7) It is not clear how the gnuradio UHD sink block handles the sample >> >> rate value in the presence of tx_time tags. For example, if I generate >> >> 10 small packets each of which has a tx_sob,tx_time and tx_eob and 0.1 >> >> sec delay between the times, and all of these small packets are put >> >> into the transmit fifo at once, then what happens? What is the rate >> >> that the UHD sink block will consume this data? It cannot be the >> >> sample rate, because these tags point to the future, so the >> >> consumption rate should be reduced, but is it what happens? Will the >> >> code switch the TX/RX switch to RX between the small packets if all >> >> those are already in the queue? >> >> >> >> I hope someone has answers to these questions. Searching the internet >> >> turned up next to nothing on these subjects. >> >> >> >> Miklos >> >> >> >> _______________________________________________ >> >> Discuss-gnuradio mailing list >> >> Discuss-gnuradio@gnu.org >> >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> > >> > >> > >
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