back to article Tick-tock, Facebook: Not a reference to that short vid horsepuckey but a literal open-source timekeeper

Facebook has taken a break from its social media shenanigans to open-source the specifications for its timekeeping device, the Open Compute Time Appliance. Basically, it's a PCI Express card that uses a Global Navigation Satellite System (GNSS) and oscillator to provide an authoritative source of time. Stick the card into a …

  1. Martin an gof Silver badge

    I suppose it depends how accurate you need to be. For most people, just synchronising the OS's clock to NTP every now and then will be perfectly sufficient, but there must be further use-cases. When I worked in ILR, we only needed accuracy to (say) half a second, in order to be able to synchronise between local and network content (put the fader up for IRN at the right moment), but to do so we had a receiver in the racks which synchronised to Rugby or DSF, that receiver itself had a laser-trimmed quartz crystal in case of loss of the LW signals, and it sent out pulses over a serial link to wall clocks in the studios, each of which had a standard (if fairly high-quality) quartz movement which could certainly keep them close enough to Rugby for several hours - possibly days, given how stable the studio temperatures were - just in case the serial link went down. No GPS (or at least, no civilian GPS) in those days, but even if there had been I suspect we'd have had a similar fail-safe cascade.

    As for the Time Appliance, I like the casual throw-away phrase used for backup:

    An oscillator (such as an atomic clock) backs things up

    Yeah, I have a couple of those in a box in the attic somewhere, gimme a moment...


    1. short

      You mock, but rubidium boxes with plenty of life left are only £150 or so, it's unlikely to be the limiting factor here.

      (The CSAC module that this design uses is spiffy, being small, low power an decent spec, but doesn't seem to be purchasable. That might just be an export control thing, mind)

    2. Fruit and Nutcase Silver badge
      1. Martin an gof Silver badge

        Re: MAC

        Wow. I didn't realise things had moved so far. £150 for a second-hand device might be a bit of an ask for a typical enterprise network, especially when NTP is generally very reliable and GNSS can be used as well, but those devices from Microchip - a company I've always admired for bringing "odd devices I never knew I needed" to the market - look fantastic. They don't appear easy to get in one-off quantities from the likes of RS or Farnell, neither of which seems to stock them...


  2. Androgynous Cupboard Silver badge

    Just the ticket!

    Ideal for the datacenter, with its clear view of the sky.

  3. chivo243 Silver badge


    FB time appliance? Will FB slurp user data via a NTP protocol?

    1. D. Evans

      Re: Why?

      As you say, why?

      Even Microsoft, finally uses NTP for it's clock.

      This makes no sense, much like FaceBook.

  4. short

    So they've opened the source code, except for the interesting bit.

    Oh, interesting. I'd love to see how they did the fpga, I've a bit of a time-nuts thing going on here, and the published specs look good.

    <rummage on github>


    I've got plenty of suitable FPGA boards, GNSS boards and a handy rubidium oscillator, fancy having a go. Somewhat disappointed that there's a bitstream file, and that's it.

    To be slightly fair, there's a bit of pdf documentation of the FPGA, but that's pushing 'open source' beyond breaking point.

    Oh well. Teasers.

    1. elsergiovolador Silver badge

      Re: So they've opened the source code, except for the interesting bit.

      Wouldn't FPGA have more jitter than a bit of old 74xx and a good crystal?

      1. short

        Re: So they've opened the source code, except for the interesting bit.

        Good grief, no. FPGAs are quite good at this sort of thing. For a start, you can clock them faster than the edge speed of a 74xx, and you can build tunable tapped delay lines by stringing logic carefully in straight lines. Single nanoseconds are fair game, better with effort. These are all things I was looking forward to seeing how they'd implemented.

        Rubidium oscillators are a bit jittery at this level, a good quartz oscillator is less jittery but less stable longer term.

  5. Anonymous Coward
    Anonymous Coward

    I suspect I may know why ..

    .. FB needs extremely accurate timing to sync events acoss all their databases.

    This is to identify those pesky people with privacy filters - you can still connect events across time.

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