Hi all, For those interested in White Rabbit, Xilinx have an article in their Xcell journal (91). The link is here <http://issuu.com/xcelljournal/docs/xcell_journal_issue_91/18?e>.
regards, Andrew On Thu, May 7, 2015 at 1:45 AM, <casper-requ...@lists.berkeley.edu> wrote: > Send casper mailing list submissions to > casper@lists.berkeley.edu > > To subscribe or unsubscribe via the World Wide Web, visit > > https://calmail.berkeley.edu/manage/list/listinfo/casper@lists.berkeley.edu > > or, via email, send a message with subject or body 'help' to > casper-requ...@lists.berkeley.edu > > You can reach the person managing the list at > casper-ow...@lists.berkeley.edu > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of casper digest..." > > > Today's Topics: > > 1. Re: Timing distribution over fiber (Jack Hickish) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 06 May 2015 23:45:53 +0000 > From: Jack Hickish <jackhick...@gmail.com> > Subject: Re: [casper] Timing distribution over fiber > To: Johan Burger <jbur...@ska.ac.za>, Michael Inggs > <miki...@gmail.com>, Bob Stricklin <bstr...@n5brg.com>, Sias > Malan > <s...@ska.ac.za>, Renier Siebrits <ren...@ska.ac.za>, > Francois Kapp > <franc...@ska.ac.za>, Etienne Bauermeister <etie...@ska.ac.za> > Cc: Simon Lewis <simonacle...@hotmail.com>, Casper Lists > <casper@lists.berkeley.edu>, Thomas Abbott <tabb...@ska.ac.za>, > Stephan Sandenberg <ssandenbe...@gmail.com> > Message-ID: > <CAG1GKS=5fWeJ+quOj= > gj_rd7qgtngc2z_07abtx7nwjhojw...@mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > On Wed, 6 May 2015 at 07:35 Johan Burger <jbur...@ska.ac.za> wrote: > > > > > Hi there, > > > > Do you maybe have any idea of requirement specifications for the HERA's > RF > > phase stability and time (?) - this might determine what technology could > > be appropriate. > > > > Hi Johan, > > Thanks for your response. We're sampling at 500 MHz, so we'd like to have a > stability of "few" degrees, preferably over timescales of many hours but > perhaps more reasonably on a calibration cadence of O(10 minutes) > > PPS is not such a big deal, and synchronization to a couple of ADC clock > cycles is probably fine. We're investigating simple-ish ways to calibrate > these out with signal injection. > > > > > > > We at SKA Africa have after some iteration come up, with a precision RF > > distribution system for many antennas. The type of laser and integrated > > modulator have been proven in the field on large arrays (not just > > MeerKAT). The RF can be directly transmitted (in our case up to 2-3 GHz > > limited by our synthesizer - the precise frequency is 1.712GHz). 500MHz > RF > > over fibre can be done by this as well. There is conditioning of the RF > > taking place on MeerKAT at the receiving end. As Jason said, not any or > all > > modules really do the job properly - we converged on a solution after > > testing, that implicitly included modules evaluated from KAT-7 days, and > > more recent modules from other manufacturers. > > > > "Low precision" timing ~100ns can indeed be done using PTP. If PPS is > > required instead of an Ethernet package a special conversion board (PCIe) > > is necessary. This is really enough for fringe finding - used in MeerKAT > > S-band for example. That digitiser is mounted in an RFI shielded pedestal > > of the antenna though. We supply the high precision PPS using our custom > > system as described below. > > > > For our L-band digitisers mounted on the outside we had to come up with > > special low power, low cost, high accuracy solution - this is being > > implemented by Renier and Etienne and others here at SKA Africa (so a > joint > > effort by our time and frequency and digitiser team). The reason is that > > White Rabbit is not compatible with 10Gbe links used on this system. > > Furthermore Ethernet is actually quite noisy as per MeerKAT measurements, > > and White Rabbit and PTP uses that (and with highish power consumption > and > > largish board size), and is not preferable in a high purity clock signal > > and PPS module. We found that measurement based PPS system will meet our > > requirements though, for stabilized links and provides us with accurate > > absolute time references at antennas, using analog methodologies. This > for > > example being important in pulsar science. > > > > I am not sure what level of RFI shielding you would be able to mount > > around modules, but as said RFI from Ethernet has certainly been found to > > be an RFI culprit, and cannot be therefore be used in MeerKAT close to > > sensitive modules - and needs to separately shielded. This therefore > means > > that if PPS is generated from White Rabbit/PTP there is still some > > uncertain propagation paths left (important at least for MeerKAT) up to > the > > point of digitization where a timing edge is inserted. We are using > > seperate fibres for PPS and RF, to further limit self-RFI and as it was > > found that requirements could only be met in this way. > > > > This is a good point, and something we'll make sure to keep in mind... > > Thanks again, > Jack > > > > > > > Regards > > > > Johan Burger > > > > > > > > > > > > For MeerKAT high precision timing a special PPS solution is used. There > > are seperate PPS transmitters and > > On Tue, May 5, 2015 at 7:56 PM, Michael Inggs <miki...@gmail.com> wrote: > > > >> Hi > >> > >> We have a complete White Rabbit setup, including 5km fibre test reels. > It > >> is driven by a Meinberg Plenum 1 clock. We are quite happy to chat with > >> anyone on this topic of phase coherence. As you all know, the hardware > and > >> firmware is all Open Source, so as Jason mentions, easy to incorporate. > I > >> think I saw that the new CASPER card has provision for WR? Members of > the > >> team have specialised GPSDO systems developed in the lab that seem to > give > >> below 10 ns of jitter. > >> > >> Someone has tested it over 900km and beyond in Norway and sub ps jitter > >> is achieved. > >> > >> One drawback is it needs a 1Ge fibre link, which I guess means, these > >> days, its own fibre. We spoke to CERN about developing 10Ge and above, > but > >> it looks complex due to the many channels embedded in these streams. > There > >> has been some good work on sending it over microwave, but I guess that > is a > >> no-no for astronomy reserves. > >> > >> Regards > >> > >> > >> > >> On 5 May 2015 at 19:27, Jason Manley <jman...@ska.ac.za> wrote: > >> > >>> White rabbit is the version of IEEE1588 that locks bit clocks. Normal > >>> IEEE1588 doesn't do this. For this reason, (last I looked), there was > no > >>> 10G implementation. 1G speeds is the highest White Rabbit > implementation. > >>> The HW support for "normal" IEEE1588 is used to timestamp the packets > >>> without software in the loop (where the CPU will introduce jitter). > >>> > >>> But you don't necessarily need any special HW for IEEE1588... it can > all > >>> be done in a normal FPGA using the standard Xilinx 10G IP core. There > are > >>> FPGA cores available for the IEEE1588 part, so you don't have to > implement > >>> it yourself. We considered this for MeerKAT at one stage, but in the > end we > >>> couldn't achieve the required performance. It might be quite workable > for > >>> HERA, though. Anyway, just a thought. It'd save you buying special HW > and > >>> running additional fibres, if it meets your performance targets. > >>> > >>> Jason Manley > >>> CBF Manager > >>> SKA-SA > >>> > >>> Cell: +27 82 662 7726 > >>> Work: +27 21 506 7300 > >>> > >>> On 05 May 2015, at 18:49, Dan Werthimer <d...@ssl.berkeley.edu> wrote: > >>> > >>> > > >>> > > >>> > hi dave, > >>> > > >>> > i also think distributing clock and 1 PPS is simpler than IEEE1588. > >>> > > >>> > some of the IEEE1588 and white rabbit experts are here at berkeley. > >>> > see for example: > >>> > http://chess.eecs.berkeley.edu/pubs/881/dreams.pdf > >>> > > >>> > my limited understanding is that 1588 phase locks the bit clocks of > >>> > routers and switches together. 1588 routers and switches have SMA > >>> > connectors on them so you can use external maser/rubidium/GPS > >>> references. > >>> > > >>> > you can achieve spectacular accuracy and stabilitity with white > rabbit > >>> > if you employ really good oscillators at each node, > >>> > i think white rabbit can acheive 70 picosecond RMS time transfer. > >>> > > >>> > best, > >>> > > >>> > dan > >>> > > >>> > > >>> > > >>> > > >>> > > >>> > On Tue, May 5, 2015 at 8:52 AM, David MacMahon < > >>> dav...@astro.berkeley.edu> wrote: > >>> > Hi, Jason, > >>> > > >>> > I have a great deal of curiosity about IEEE-1588, but I've always > >>> wondered about the precision/stability that's attainable. Compared > with > >>> multiple sample clocks, correlating signals sampled with one common > clock > >>> seems far more forgiving vis a vis clock frequency/phase stability. > If you > >>> or John could point me to any information about this, please do! > >>> > > >>> > Thanks, > >>> > Dave > >>> > > >>> > On May 4, 2015, at 11:44 PM, Jason Manley wrote: > >>> > > >>> > > On the far end of the concept spectrum, have you considered > >>> distributing time over your existing ethernet network with IEEE-1588, > and > >>> using this to discipline local ovenised 10MHz oscs at each antenna? > >>> > > > >>> > > I'm cc'ing Johan Burger, who heads up our Timing and Frequency > >>> Reference subsystem, who might be able to offer some additional > insight. I > >>> know they've tried a few different lasers and detectors, with varying > >>> levels of success. > >>> > > > >>> > > Jason Manley > >>> > > CBF Manager > >>> > > SKA-SA > >>> > > > >>> > > Cell: +27 82 662 7726 > >>> > > Work: +27 21 506 7300 > >>> > > > >>> > > On 05 May 2015, at 5:18, Bob Stricklin <bstr...@n5brg.com> wrote: > >>> > > > >>> > >> Hi Jack and John, > >>> > >> > >>> > >> I wanted to add an input here?.. > >>> > >> > >>> > >> I am working on a 10 MHz GPS slaved reference for my personal use. > >>> I am working with a Analog Devices AD9548 Evaluation board (~$250) , > GPS > >>> with 1 PPS, and a ovenized 10 MHz osc. I also plan to distribute this > clock > >>> and have considered the Avago fiber product line. One of the older > >>> generation Avago fiber parts should work fine for <$25 per channel. > With > >>> careful control of lengths and delays it should be possible to maintain > >>> good phasing between channels. The analog devices chip is <$50 so a > custom > >>> solution should be <$500/reference but with considerable development > time. > >>> > >> > >>> > >> Bob Stricklin > >>> > >> > >>> > >> > >>> > >>> On May 4, 2015, at 10:02 PM, Jack Hickish <jackhick...@gmail.com > > > >>> wrote: > >>> > >>> > >>> > >>> Hi John, > >>> > >>> > >>> > >>> Thanks for the info. I'll add Litelink to my list of suppliers to > >>> investigate. > >>> > >>> We have no particular urge to multiplex the signals on to the > >>> fiber unless there's a particularly neat/cheap solution to do that. > There's > >>> no great appetite to go custom. We've got about ~30 nodes, and my first > >>> stab at getting an off-the-shelf solution turned up at a few k$ / > node, not > >>> including any cleanup electronics. > >>> > >>> > >>> > >>> Thanks again, > >>> > >>> > >>> > >>> Jack > >>> > >>> > >>> > >>> On Mon, 4 May 2015 at 19:25 John Ford <jf...@nrao.edu> wrote: > >>> > >>>> Hi CASPERites, > >>> > >>>> > >>> > >>>> For HERA, we're looking at distributing timing signals (PPS & > >>> 10Mhz ref or > >>> > >>>> 500 MHz clock) over O(100m) fibers to various digitization > nodes. > >>> > >>>> I figure some folks in CASPERland have experience with this kind > >>> of > >>> > >>>> system? > >>> > >>>> Did you use custom RF-over-fiber kit, or off-the-shelf PPS/10MHz > >>> > >>>> solutions? > >>> > >>>> Any words of wisdom/caution to share? > >>> > >>>> > >>> > >>>> Any responses much appreciated! > >>> > >>> > >>> > >>> We have several different schemes for the different signals. Are > >>> you > >>> > >>> planning for one fiber per signal per node? or one fiber with > the > >>> signals > >>> > >>> multiplexed on them? > >>> > >>> > >>> > >>> If the signals are one per signal, you can use some off-the-shelf > >>> > >>> solutions, but they are kind of pricey, and if you have a lot of > >>> nodes to > >>> > >>> supply, it might be worth working on something custom. We have > >>> used Math > >>> > >>> Associates stuff for this kind of work. Math Associates is now > >>> litelink, > >>> > >>> and they tout the affordability of their stuff, so maybe it's > >>> > >>> reasonable... > >>> > >>> > >>> > >>> > >>> > >>> On the 10 MHz, we send the 10 MHz reference over fiber, and at > the > >>> far end > >>> > >>> use a crystal oscillator locked to the reference to clean up the > >>> noise > >>> > >>> from the fiber electronics. This is essential for > interferometry, > >>> but > >>> > >>> maybe not for single-dish use. > >>> > >>> > >>> > >>> John > >>> > >>> > >>> > >>>> > >>> > >>>> Jack > >>> > >>>> > >>> > >>> > >>> > >>> > >>> > >> > >>> > > > >>> > > > >>> > > >>> > > >>> > > >>> > >>> > >>> > >> > >> > >> -- > >> Michael Inggs > >> Department of Electrical Engineering, University of Cape Town, Private > >> Bag, Rondebosch 7701, South Africa. Tel: +27 21 650 2799 Fax: +27 21 > 650 > >> 3465 Skype: mikings > >> "Ex Africa semper aliquid novi" > >> > >> > > > -------------- next part -------------- > An HTML attachment scrubbed and removed. > HTML attachments are only available in MIME digests. > > End of casper Digest, Vol 90, Issue 10 > ************************************** > -- Dr Andrew van der Byl Mobile: +27 83 312 7392 Email: a <andrew.vander...@gmail.com>vd...@gmail.com
