Using mode byte of NMEA ref.clock driver ? - NTP

This is a discussion on Using mode byte of NMEA ref.clock driver ? - NTP ; Hi Folks, I have been posting to the NTP 'questions mailing' list regarding modification of NMEA refclock driver. The current driver implementation supports 4800 baudrate, GPGGA, GPGLL and GPRMC sentences. We are using Accord's GPS Clock which generates NMEA sentences ...

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Thread: Using mode byte of NMEA ref.clock driver ?

  1. Using mode byte of NMEA ref.clock driver ?

    Hi Folks,

    I have been posting to the NTP 'questions mailing' list regarding
    modification of
    NMEA refclock driver. The current driver implementation supports 4800
    baudrate,
    GPGGA, GPGLL and GPRMC sentences.

    We are using Accord's GPS Clock which generates NMEA sentences at 9600B.
    It also generates 1PPS and a custom NMEA sentence with GPS time-stamp.

    I've done few modifications to interface this with NTP.

    1. Support for 4800 and 9600
    2. Parsing of custom NMEA sentence

    After going through the NMEA ref.clock driver, it seems that the
    original author has choosen values 0(GPXXX), 1(GPRMC), 2(GPGGA) and
    4(GPGLL) for mode field so that multiple sentences can be selected. As
    posted earlier reg. using the mode byte /field to support Accord GPS
    Clock, fourth bit cannot be used to denote the baudrate.

    Fourth bit can denote GPZDG(8) (custom NMEA format) while the fifth
    bit can be used for baudrate 0(4800) and 1(9600). But in this case
    multiple sentences may be allowed only if the value of last four bits
    is less than 8, because GPZDG gives GPS time and not UTC like rest of
    them. So if GPZDG is selected, others sentences should not be
    selected.

    I need comments and suggestions from folks who have been maintaining
    reference clock drivers regarding the suggested changes and its implications
    if any.

    Venu

  2. Re: Using mode byte of NMEA ref.clock driver ?

    Venu,

    I'd say goferit.

    If somebody creates a config file with incompatible flags you can either:

    - quietly do what they say
    - noisily do what they say
    - noisily disallow them

    There are other choices, but those seem to me to be the best choices.
    --
    Harlan Stenn
    http://ntpforum.isc.org - be a member!

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