Preffered OS for a GPS based stratum 1 - NTP

This is a discussion on Preffered OS for a GPS based stratum 1 - NTP ; I've dug up an Oncore GT+ GPS receiver, matching antenna, and PPS stretching converter box. WinOncore shows a 'Time Solution one sigma' of 38ns, so it seems to be an acceptable ref clock for my purposes. After surveying the computing ...

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Thread: Preffered OS for a GPS based stratum 1

  1. Preffered OS for a GPS based stratum 1

    I've dug up an Oncore GT+ GPS receiver, matching antenna, and PPS
    stretching converter box. WinOncore shows a 'Time Solution one sigma'
    of 38ns, so it seems to be an acceptable ref clock for my purposes.

    After surveying the computing hardware available, a Sun Ultra10 seems
    to keep the best time and is otherwise unused.

    What OS do you recomend for the Ultra? Off the top of my head, I'm
    considering Solaris (is there PPS support in Solaris 10?), FreeBSD or
    NetBSD. My understanding is Linux 2.6 PPS support is rough at best.

    Cheers,
    ~Spiffed


  2. Re: Preffered OS for a GPS based stratum 1

    Spiffed writes:

    > I've dug up an Oncore GT+ GPS receiver, matching antenna, and PPS
    > stretching converter box. WinOncore shows a 'Time Solution one sigma'
    > of 38ns, so it seems to be an acceptable ref clock for my purposes.
    >
    > After surveying the computing hardware available, a Sun Ultra10 seems
    > to keep the best time and is otherwise unused.
    >
    > What OS do you recomend for the Ultra? Off the top of my head, I'm
    > considering Solaris (is there PPS support in Solaris 10?), FreeBSD or
    > NetBSD. My understanding is Linux 2.6 PPS support is rough at best.
    >
    > Cheers,
    > ~Spiffed
    >


    Yes, solaris has had PPS support for a long time, since around 2.6 IIRC.

  3. Re: Preffered OS for a GPS based stratum 1

    Spiffed wrote:
    > I've dug up an Oncore GT+ GPS receiver, matching antenna, and PPS
    > stretching converter box. WinOncore shows a 'Time Solution one sigma' of
    > 38ns, so it seems to be an acceptable ref clock for my purposes.
    >
    > After surveying the computing hardware available, a Sun Ultra10 seems to
    > keep the best time and is otherwise unused.
    >
    > What OS do you recomend for the Ultra? Off the top of my head, I'm
    > considering Solaris (is there PPS support in Solaris 10?), FreeBSD or
    > NetBSD. My understanding is Linux 2.6 PPS support is rough at best.


    FreeBSD is the canonical OS for a PPS box, search for some of phk's
    articles on this subject!

    Terje

    --
    -
    "almost all programming can be viewed as an exercise in caching"

  4. Re: Preffered OS for a GPS based stratum 1

    > From: Terje Mathisen
    > Date: Fri, 31 Oct 2008 08:59:06 +0100
    > Sender: questions-bounces+oberman=es.net@lists.ntp.org
    >
    >
    > Spiffed wrote:
    > > I've dug up an Oncore GT+ GPS receiver, matching antenna, and PPS
    > > stretching converter box. WinOncore shows a 'Time Solution one sigma' of
    > > 38ns, so it seems to be an acceptable ref clock for my purposes.
    > >
    > > After surveying the computing hardware available, a Sun Ultra10 seems to
    > > keep the best time and is otherwise unused.
    > >
    > > What OS do you recomend for the Ultra? Off the top of my head, I'm
    > > considering Solaris (is there PPS support in Solaris 10?), FreeBSD or
    > > NetBSD. My understanding is Linux 2.6 PPS support is rough at best.

    >
    > FreeBSD is the canonical OS for a PPS box, search for some of phk's
    > articles on this subject!


    Seconded. FreeBSD has taken ntp and timing as a priority for a very long
    time. I know that back in the days when BSD was still being developed at
    Berkeley, they counted the instructions used by the PPS kernel code and
    then used the clock frequency to correct the time for that delay.

    N.B., with any system, don't expect really good time if the CPU uses
    power management tools that change the frequency of the CPU while NTP is
    running. Your probably better off with a single CPU system.
    --
    R. Kevin Oberman, Network Engineer
    Energy Sciences Network (ESnet)
    Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
    E-mail: oberman@es.net Phone: +1 510 486-8634
    Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751

  5. Re: Preffered OS for a GPS based stratum 1

    Terje Mathisen writes:

    >Spiffed wrote:
    >> I've dug up an Oncore GT+ GPS receiver, matching antenna, and PPS
    >> stretching converter box. WinOncore shows a 'Time Solution one sigma' of
    >> 38ns, so it seems to be an acceptable ref clock for my purposes.
    >>
    >> After surveying the computing hardware available, a Sun Ultra10 seems to
    >> keep the best time and is otherwise unused.
    >>
    >> What OS do you recomend for the Ultra? Off the top of my head, I'm
    >> considering Solaris (is there PPS support in Solaris 10?), FreeBSD or
    >> NetBSD. My understanding is Linux 2.6 PPS support is rough at best.


    Depends on what you want. PPS support probably does not belong in the
    kernel anyway. You really need to examine the pps signals to make sure that
    they are sane (eg roughly one second between successive signals, etc) and
    the kernel is no place to be doing those sanity checks. Handling the PPS is
    userspace is perhaps slightly cruder (getting the time in kernel space may
    be slightly faster) but you could do an interrupt driven system where the
    PPS triggers and interrupt whose only pupose is to get the time at which
    the interrupt occured. Then those data values are massaged, filtered,
    whatever, to give the data for ntp to discipline the kernel. I do that (PPS
    onto a parallel interrupt which is times by an interrupt service routine,
    and that data is placed onto /dev/gpsint device to be read off by userland
    routines to feed to ntp via the shm refclock driver. I get about 2usec
    resolution/accuracy as read from the scatter of the offset readings-- since
    I have no way of independtly timing the gps timing routing. How much of
    that is due to the ntp behaving badly in tracking rate changes of the cpu
    clock, and how much is inherent I do not know. But since the clock on Linux
    is 1usec quantization and the accuracy of my gps is 1 usec, I figure this
    is about as good as it gets. I doubt that you can get consistant reading of
    the cpu clock even from the kenrel to better than about 1us, whether on
    linux or on BSD.




    >FreeBSD is the canonical OS for a PPS box, search for some of phk's
    >articles on this subject!


    Ie, I do not know what the problem with Linux is.


    >Terje


    >--
    >-
    >"almost all programming can be viewed as an exercise in caching"


  6. Re: Preffered OS for a GPS based stratum 1

    oberman@es.net (Kevin Oberman) writes:

    >> From: Terje Mathisen
    >> Date: Fri, 31 Oct 2008 08:59:06 +0100
    >> Sender: questions-bounces+oberman=es.net@lists.ntp.org
    >>
    >>
    >> Spiffed wrote:
    >> > I've dug up an Oncore GT+ GPS receiver, matching antenna, and PPS
    >> > stretching converter box. WinOncore shows a 'Time Solution one sigma' of
    >> > 38ns, so it seems to be an acceptable ref clock for my purposes.
    >> >
    >> > After surveying the computing hardware available, a Sun Ultra10 seems to
    >> > keep the best time and is otherwise unused.
    >> >
    >> > What OS do you recomend for the Ultra? Off the top of my head, I'm
    >> > considering Solaris (is there PPS support in Solaris 10?), FreeBSD or
    >> > NetBSD. My understanding is Linux 2.6 PPS support is rough at best.

    >>
    >> FreeBSD is the canonical OS for a PPS box, search for some of phk's
    >> articles on this subject!


    >Seconded. FreeBSD has taken ntp and timing as a priority for a very long
    >time. I know that back in the days when BSD was still being developed at
    >Berkeley, they counted the instructions used by the PPS kernel code and
    >then used the clock frequency to correct the time for that delay.


    That is of course less of an issue with CPUs running at 2GHz than it was
    for CPUs running at 40KHz.


    >N.B., with any system, don't expect really good time if the CPU uses
    >power management tools that change the frequency of the CPU while NTP is
    >running. Your probably better off with a single CPU system.


    Should be OK if the system uses something like HPET for the timing rather
    than cpu instruction cycles. Mind you on linux, the whole timing routines
    are in a bit of a mess right now it seems. But maybe that is also true of
    BSD.


    >--
    >R. Kevin Oberman, Network Engineer
    >Energy Sciences Network (ESnet)
    >Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
    >E-mail: oberman@es.net Phone: +1 510 486-8634
    >Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751


  7. Re: Preffered OS for a GPS based stratum 1

    Kevin Oberman wrote:
    > Seconded. FreeBSD has taken ntp and timing as a priority for a very
    > long time. I know that back in the days when BSD was still being
    > developed at Berkeley, they counted the instructions used by the PPS
    > kernel code and then used the clock frequency to correct the time
    > for that delay.


    I'd have thought that it wasn't the instruction count that mattered
    but the cycle count? Admittedly, instructions/frequency is closer
    than nothing but given that a single cache miss is O(100)
    instructions... so, snap CR16 (PA-RISC interval counter) or its
    equivalent (assuming there is one and reading it isn't too nasty) on
    entry and exit.

    rick jones
    --
    The computing industry isn't as much a game of "Follow The Leader" as
    it is one of "Ring Around the Rosy" or perhaps "Duck Duck Goose."
    - Rick Jones
    these opinions are mine, all mine; HP might not want them anyway...
    feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

  8. Re: Preffered OS for a GPS based stratum 1

    Unruh wrote:
    > clock, and how much is inherent I do not know. But since the clock on Linux
    > is 1usec quantization and the accuracy of my gps is 1 usec, I figure this
    > is about as good as it gets. I doubt that you can get consistant reading of
    > the cpu clock even from the kenrel to better than about 1us, whether on
    > linux or on BSD.


    Famous last words? :-)

    PHK has setup several FreeBSD-based refclocks that measure out well
    below the 1 us level, i.e. take a look at:

    http://people.freebsd.org/~phk/

    A quote from that page:

    "Current status is that I can track my GPS receiver into a band less
    than 150 nsec wide around true UTC. This is an order of magnitude better
    than any other UNIX system I know of. My performance is probably even
    better than that, but I have not had much chance to validate it yet."

    Terje
    --
    -
    "almost all programming can be viewed as an exercise in caching"

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