[ntp:questions] PPS on Linux status?

Martin Karsten mkarsten_NOSPAM_ at uwaterloo.ca
Tue May 15 02:15:52 UTC 2007

David (and also Michael),

thanks very much for you responses! Yes, FreeBSD works like a charm.
;-)  Just a quick follow-up, since I'm rather a software than a hardware

Does the need for a level converter depend on the hardware or software
in use? I.e. will Linux/i386 (with the patch set) or Solaris on Sparc or
i386 generally require a level converter or work with a GPS clock out of
the box? This assumes that the GPS receiver is connected via serial
input. Or do GPS clocks already include this conversion these days?

My FreeBSD setup involves an old integrated gadget that someone built
for me many years ago and I don't know the details of PPS level conversion.

Thanks again,

David L. Mills wrote:
> Marten,
> The full functionality for precision kernel and PPS is in Solaris,
> FreeBSD and Alpha Tru64 (kernel option). FreeBSD works best for me using
> the pps driver (kernel option), since no level converter is required and
> the DCD is not an issue.
> The PPSKit is specific to Linux and an API for it is in no other system
> known to me. The full API for the systems mentioned above is defined in
> RFC-2783.
> Martin Karsten wrote:
>> My apologies if I am beating a dead horse, but I've spent several hours
>> today searching for a definite answer to the subject line question.
>> The PPS part of the ntp documentation at one point refers to the PPSkit
>> for Linux and at another point says "The FreeBSD, Linux and Solaris
>> implementations can be used with the stock kernels provided with those
>> systems;" about the ntp PPS driver.
>> I understand that a full-scale PPS "system" in the kernel (and the PPS
>> api) may not be needed to get ntp working with PPS (e.g. that seems to
>> be the case for Solaris), but at least some level of support is probably
>> required from the kernel (in the serial driver)? Does the stock Linux
>> kernel (e.g. any recent 2.6 variant) support PPS or do I have to use an
>> extension such as PPSkit to use a PPS signal on Linux for ntpd?
>> I have a setup (server GPS/PPS) for which on a FreeBSD
>> machine, ntptime shows the PPSSIGNAL status bit, but not on Linux.
>> Any help would be greatly appreciated.
>> Thanks,
>> Martin

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