Say we need +-10ms accuracy in timestamps. Precision Time Protocol in LAN should sync PC's clocks with enough accuracy. And then using USRP-like methods - set current/start time - get first sample in known time? Of course USB will add undetermined delays but no external GPS required.
On Wed, 2017-08-16 at 16:57 +0100, Derek Kozel wrote: > It should be pointed out that the hardware based timestamping is only needed > if you need time alignment better than a > half second or so. With USB transfers, various buffers, NTP based alignment > of the host computer's time, and some > extra code on the host side you could do a coarse time alignment, probably > with less than a half second of error. > > You could also time align the streams if both radios receive the same signal > and you know the distance (and other > details depending on the precision needed) between the transmitter and your > two receivers. This is done by many > protocols like the cellular standards to create a distributed timebase, but > quickly becomes non-trivial. > > The B200 does timestamping in the FPGA and can use a 1PPS signal to align to > GPS time. It is more expensive than the > HackRF, but much less than the $3000 mentioned above. > > On Wed, Aug 16, 2017 at 4:20 PM, Sylvain Munaut <246...@gmail.com> wrote: > > On Wed, Aug 16, 2017 at 5:11 PM, <b.shube...@sirinsoftware.com> wrote: > > > What type of hardware? I thought from hardware point of view only precise > > > clock is required and all the other > > things in > > > firmware. I've naively thought i could modify hackrf firmware to get this > > > feature. > > > > Mostly a FPGA and a PPS input from a GPS receiver. > > > > Each individual sample has a timestamp of when it has been received. > > And you can also reset the timestamp on the next PPS edge. > > > > Technically it would be possible to modify the hackrf firmware and > > repurpose some GPIOs and have all samples transmitted to the host be > > in timestamped packets and implements timestamping in the on-board > > ARM. > > For additional hardware you'd only need an external GPS receiver (or > > some other way to have both a single freq reference + single sync > > pulse). > > > > Cheers, > > > > Sylvain > > > > _______________________________________________ > > 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
