See this post in context http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2012-September/005352.html
On Mon, Jun 10, 2013 at 7:13 AM, Marcus Leech <mle...@ripnet.com> wrote: > I believe that they are all dropped, but Josh can comment more > definitively. > > > on Jun 10, 2013, *Sean Nowlan* <sean.now...@gtri.gatech.edu> wrote: > > Do late packets always get dropped by the USRP? What happens if its > buffers get filled up with samples, all of which are late? > > "Marcus D. Leech" <mle...@ripnet.com> wrote: > > >> L = late packet, there was a time on the packet which was> time on > >> device when > >> > >> > >There are two different "cases" for late packets happening. > > > >The first is that you haven't sent your packet far enough in advance to > >account for latency variations on the host. Unfortunately, on a > >general-purpose > > OS like Windows or Linux, latency variability can be extreme, and for > >long-running flow-graphs you might need to develop a good model to > determine > > what the worst-case is and account for that. > > > >The second is that the clock on the USRP and the clock on the host will > >tend to drift apart over time, particularly if both of them are "free > >running". > > So when you schedule timed bursts far enough in advance during the > >start of a "session", it's entirely possible that after quite some time, > the > > two clocks have drifted apart unfavourably in terms of allowing you > >to schedule things far enough in advance, relative to the USRP clock. > > PC clocks are *terrible* by themselves. They'll drift significant > >fractions of a second on a daily basis without any outside steering. > > The USRP > > clock, even free-running, is typically much, much better. > > > > > >-- > >Marcus Leech > >Principal Investigator > >Shirleys Bay Radio Astronomy Consortium > >http://www.sbrac.org > > > > > >_______________________________________________ > >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 > >
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