in a somewhat related question. can anybody give us advice about GPS disciplined oscillators time/freq standards that are very accurate wrt UTC? we don't want to buy a hydrogen maser (too pricy). we have been looking at a company called endrun technologies that sell time/freq standards accurate to about +-10 ns wrt UTC. they might be able to match a pair of them that track each other +- 3ns RMS. we need a pair of well matched time/freq standards for coincidence time stamping/correlation between two observatories for our panoseti experiment. (the two optical/IR observatories are 500 km apart, and don't have masers).
thanks for any advice on this. btw, we are using white rabbit for time/frequency distribution over 1 Gbe bidi fiber, and we put the white rabbit hardware (VCO and DAC chips) and software on our FPGA boards for this project. (we made our own FPGA boards with white rabbit and kintex7 because we need a few thousand boards) white rabbit does sub-ns accuracy in timing distribution - some white rabbit users have measured 30 ps RMS. best wishes, dan On Thu, Mar 7, 2019 at 12:05 AM Michael Inggs <miki...@gmail.com> wrote: > Hi Franco > > Simon Lewis in the RRSG at UCT has White Rabbit hardware and expertise > (PhD incubating). Snag is that it runs on 1GE Fibre. We also have a GPS > version. The former gives sub ns precision, the latter about 4 ns rms. Send > me a message off line and I can link you. We also have a scheme of aligning > a trigger to both a local MHz clock and the 1 pps. This is all open source > hardware and software. > > Regards > > On Thu, 7 Mar 2019 at 08:52, James Smith <jsm...@ska.ac.za> wrote: > >> Hello Franco, >> >> As I understand it, PTP wasn't terribly useful in our application (though >> I wasn't involved with this directly). You can probably sync the little >> Linux instance that runs on the ROACH2, but getting the time information >> onto your FPGA may prove somewhat tricky. >> >> Are you using an ADC card in the ROACH2? Or is the data digitised >> separately? >> >> What we've done with ROACH and ROACH2 designs in the past is more or less >> this: >> >> - FPGA's clock comes from a timing & frequency reference (TFR). >> - ROACH2 gets a 1PPS input from the same TFR. >> - In the FPGA logic there's a counter which is reset as part of the >> initialisation, and some logic that starts the counter going after a set >> number of 1PPS pulses (two to three, I forget exactly now). >> - The output of this counter is pipelined along with the data and >> then sent out as part of the SPEAD data on the 10GbE network. >> >> The idea here being that you know with a fairly high degree of precision >> which pulse your ROACH was initialised on. The counter that comes through >> on the SPEAD packet counts in FPGA clock cycles (or multiples thereof, >> perhaps you might want to count in spectra), and then you can use the start >> time to calculate the timestamp of each packet (Unix time, MJD, whichever >> your preferred reference is). >> >> Hope that helps. >> >> Regards, >> James >> >> >> On Wed, Mar 6, 2019 at 7:41 PM Franco <francocuro...@gmail.com> wrote: >> >>> Dear Casperiites, >>> >>> I was given the task of timestamping ROACH2 spectral data in a telescope >>> that uses PTP (precision time protocol) as a synchronization protocol. I >>> understand that ROACH's BORPH come preloaded with NTP (network time >>> protocol) libraries/daemos, but PTP is preferred because is already in use >>> in the telescope, and it achieves greater time precision. >>> >>> Does somebody know if it is feasible to compile/install PTP libraries in >>> BORPH? >>> >>> Alternatively, we have though of sending the ROACH the current time >>> through a GPIO pin using IRIG-B timecode standard. Has anybody done >>> something similar in the past? >>> >>> Thanks, >>> >>> Franco >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "casper@lists.berkeley.edu" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to casper+unsubscr...@lists.berkeley.edu. >>> To post to this group, send email to casper@lists.berkeley.edu. >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "casper@lists.berkeley.edu" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to casper+unsubscr...@lists.berkeley.edu. >> To post to this group, send email to casper@lists.berkeley.edu. >> > > > -- > Michael Inggs > 10 Devon Street, Simon's Town, South Africa. Tel: +27 21 786 1723 Fax: +27 > 21 786 1151 Skype: mikings Cell: +27 83 776 7304 > "Ex Africa semper aliquid novi" > > -- > You received this message because you are subscribed to the Google Groups " > casper@lists.berkeley.edu" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to casper+unsubscr...@lists.berkeley.edu. > To post to this group, send email to casper@lists.berkeley.edu. > -- You received this message because you are subscribed to the Google Groups "casper@lists.berkeley.edu" group. To unsubscribe from this group and stop receiving emails from it, send an email to casper+unsubscr...@lists.berkeley.edu. To post to this group, send email to casper@lists.berkeley.edu.
