Fabian and Derek, Thanks for your comments,
Yesterday I realized that 10GbE could not support my 100MSymps, complex dual channel output. That's why I've seen underflow messages. I actually have got around this underflow by putting (ms) delay between bursts. However, it seems like that there's something going on even if I dont see any underflow message after the delay.. So I'd like to know what happens how the buffers are managed especially in 2 channel case.. Q1 : In 2 channel case, does the tx buffer divided into half size ? Q2 : Do the two tx buffers are filled up simultaneously or one after another? Q3 : when underflow happens, does the kernel wait until the 2 channel buffers are filled up ? or it just starts to output as soon as the first channel buffer is filled while the second is being filled? If I got answers about these questions, the delayed output on the dual channel can be explained more clearly... Thanks, Young C. Park On Tue, Jul 31, 2018 at 12:45 AM, Derek Kozel via USRP-users < usrp-users@lists.ettus.com> wrote: > Hello Fabian and Young, > > The suggestion about timed commands is on point, I think that is what is > missing. Using unknown PPS will not hurt as there are two radio blocks with > timekeepers and using the unknown PPS setting, or external or gpsdo if > installed, will ensure that they are aligned. > > > 3) If that does not work, maybe the FPGA can handly only one command at > a time - even if you tell him to execute two. Then it may be possible to > start one command timed before the other and extend that sequence of > samples with the correct amount of zeros. > > Each radio channel has it's own queue for timed commands so it is possible > to schedule all channels simultaneously. > > Derek > > On Mon, Jul 30, 2018 at 8:08 AM, Fabian Schwartau via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> Hi Young, >> >> I am not an expert, but I have three suggestions: >> 1) Using 'Unknown PSS' or any other sync method should not have no >> affect, as this is for syncing two or more USRPs. You have only one FPGA >> and that is in sync with itself ;) >> 2) Did you tried using timed commands? (see function set_command_time()) >> 3) If that does not work, maybe the FPGA can handly only one command at a >> time - even if you tell him to execute two. Then it may be possible to >> start one command timed before the other and extend that sequence of >> samples with the correct amount of zeros. >> >> Best regards, >> Fabian >> >> Am 30.07.2018 um 08:34 schrieb YoungC_Park via USRP-users: >> >>> Hi all, >>> >>> I hope someone could help me on my situation. I could not find similar >>> cases on the usrp archive. >>> >>> I have one USRP X310 that has UBX-160(slot A) , LFTX board(slot B) and >>> GPS module installed. >>> >>> - my UHD is 3.11.0 >>> >>> - Using uhd API based on tx_samples from_file.cpp, I can generate dual >>> output bursts from UBX160 and LFTX with 200MHz master clock and 100Msps on >>> USRP X310. >>> >>> - However, the second output (ch 1, red in the picture) is lagged from >>> the first one (ch 0, yellow) by about (~10us with +-4us uncertainty) >>> >>> - The baseband burst is a sawtooth waveform of two cycles(2000 samples >>> long). and UBX160 modulates it into fc = 1GHz whereas LFTX generates it as >>> is. >>> >>> - This lagging is quite constant (10us) even if I change the sampling >>> rate (10,20,50, 100MSps). >>> >>> - Tried 'Unknown PPS', 'gpsdo', 'internal',,, but no difference. >>> >>> - When I switch the order of channels to (1,0) as opposed to (0,1), then >>> the ch0 lags behind the ch1, which seems that this is related to some >>> sequenced process… >>> >>> We are seeking for helps on the cause and cure about this lagging… >>> >>> Thanks, >>> >>> Young C. Park >>> >>> >>> >>> _______________________________________________ >>> USRP-users mailing list >>> USRP-users@lists.ettus.com >>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>> >>> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > -- ------------------------ Youngcheol Park ycpark...@gmail.com
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