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 > > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
