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ntp_adjtime (2)
  • ntp_adjtime (2) ( Solaris man: Системные вызовы )
  • >> ntp_adjtime (2) ( FreeBSD man: Системные вызовы )

  • BSD mandoc
     

    NAME

    
    
    ntp_adjtime
    
     
    ntp_gettime
    
     - Network Time Protocol (NTP) daemon interface system calls
    
     
    

    LIBRARY

    Lb libc
    
     
    

    SYNOPSIS

       #include <sys/timex.h>
    int ntp_adjtime (struct timex *);
    int ntp_gettime (struct ntptimeval *);
     

    DESCRIPTION

    The two system calls ntp_adjtime ();
    and ntp_gettime ();
    are the kernel interface to the Network Time Protocol (NTP) daemon ntpd(8).

    The ntp_adjtime ();
    function is used by the NTP daemon to adjust the system clock to an externally derived time. The time offset and related variables which are set by ntp_adjtime ();
    are used by hardclock ();
    to adjust the phase and frequency of the phase- or frequency-lock loop (PLL resp. FLL) which controls the system clock.

    The ntp_gettime ();
    function provides the time, maximum error (sync distance) and estimated error (dispersion) to client user application programs.

    In the following, all variables that refer PPS are only relevant if the PPS_SYNC option is enabled in the kernel.

    ntp_adjtime ();
    has as argument a struct timex of the following form:

    struct timex {
            unsigned int modes;     /* clock mode bits (wo) */
            long offset;            /* time offset (us) (rw) */
            long freq;              /* frequency offset (scaled ppm) (rw) */
            long maxerror;          /* maximum error (us) (rw) */
            long esterror;          /* estimated error (us) (rw) */
            int status;             /* clock status bits (rw) */
            long constant;          /* pll time constant (rw) */
            long precision;         /* clock precision (us) (ro) */
            long tolerance;         /* clock frequency tolerance (scaled
                                     * ppm) (ro) */
            /*
             * The following read-only structure members are implemented
             * only if the PPS signal discipline is configured in the
             * kernel.
             */
            long ppsfreq;           /* pps frequency (scaled ppm) (ro) */
            long jitter;            /* pps jitter (us) (ro) */
            int shift;              /* interval duration (s) (shift) (ro) */
            long stabil;            /* pps stability (scaled ppm) (ro) */
            long jitcnt;            /* jitter limit exceeded (ro) */
            long calcnt;            /* calibration intervals (ro) */
            long errcnt;            /* calibration errors (ro) */
            long stbcnt;            /* stability limit exceeded (ro) */
    };
    

    The members of this struct have the following meanings when used as argument for ntp_adjtime (:);

    Fa modes
    Defines what settings should be changed with the current ntp_adjtime ();
    call (write-only). Bitwise OR of the following:

    MOD_OFFSET
    set time offset
    MOD_FREQUENCY
    set frequency offset
    MOD_MAXERROR
    set maximum time error
    MOD_ESTERROR
    set estimated time error
    MOD_STATUS
    set clock status bits
    MOD_TIMECONST
    set PLL time constant
    MOD_CLKA
    set clock A
    MOD_CLKB
    set clock B

    Fa offset
    Time offset (in microseconds), used by the PLL/FLL to adjust the system time in small increments (read-write).
    Fa freq
    Frequency offset (scaled ppm) (read-write).
    Fa maxerror
    Maximum error (in microseconds). Initialized by an ntp_adjtime ();
    call, and increased by the kernel once each second to reflect the maximum error bound growth (read-write).
    Fa esterror
    Estimated error (in microseconds). Set and read by ntp_adjtime (,);
    but unused by the kernel (read-write).
    Fa status
    System clock status bits (read-write). Bitwise OR of the following:

    STA_PLL
    Enable PLL updates (read-write).
    STA_PPSFREQ
    Enable PPS freq discipline (read-write).
    STA_PPSTIME
    Enable PPS time discipline (read-write).
    STA_FLL
    Select frequency-lock mode (read-write).
    STA_INS
    Insert leap (read-write).
    STA_DEL
    Delete leap (read-write).
    STA_UNSYNC
    Clock unsynchronized (read-write).
    STA_FREQHOLD
    Hold frequency (read-write).
    STA_PPSSIGNAL
    PPS signal present (read-only).
    STA_PPSJITTER
    PPS signal jitter exceeded (read-only).
    STA_PPSWANDER
    PPS signal wander exceeded (read-only).
    STA_PPSERROR
    PPS signal calibration error (read-only).
    STA_CLOCKERR
    Clock hardware fault (read-only).

    Fa constant
    PLL time constant, determines the bandwidth, or ``stiffness'' of the PLL (read-write).
    Fa precision
    Clock precision (in microseconds). In most cases the same as the kernel tick variable (see hz(9)). If a precision clock counter or external time-keeping signal is available, it could be much lower (and depend on the state of the signal) (read-only).
    Fa tolerance
    Maximum frequency error, or tolerance of the CPU clock oscillator (scaled ppm). Ordinarily a property of the architecture, but could change under the influence of external time-keeping signals (read-only).
    Fa ppsfreq
    PPS frequency offset produced by the frequency median filter (scaled ppm) (read-only).
    Fa jitter
    PPS jitter measured by the time median filter in microseconds (read-only).
    Fa shift
    Logarithm to base 2 of the interval duration in seconds (PPS, read-only).
    Fa stabil
    PPS stability (scaled ppm); dispersion (wander) measured by the frequency median filter (read-only).
    Fa jitcnt
    Number of seconds that have been discarded because the jitter measured by the time median filter exceeded the limit MAXTIME (PPS, read-only).
    Fa calcnt
    Count of calibration intervals (PPS, read-only).
    Fa errcnt
    Number of calibration intervals that have been discarded because the wander exceeded the limit MAXFREQ or where the calibration interval jitter exceeded two ticks (PPS, read-only).
    Fa stbcnt
    Number of calibration intervals that have been discarded because the frequency wander exceeded the limit MAXFREQ /4 (PPS, read-only).

    After the ntp_adjtime ();
    call, the struct timex structure contains the current values of the corresponding variables.

    ntp_gettime ();
    has as argument a struct ntptimeval with the following members:

    struct ntptimeval {
            struct timeval time;    /* current time (ro) */
            long maxerror;          /* maximum error (us) (ro) */
            long esterror;          /* estimated error (us) (ro) */
    };
    

    These have the following meaning:

    Fa time
    Current time (read-only).
    Fa maxerror
    Maximum error in microseconds (read-only).
    Fa esterror
    Estimated error in microseconds (read-only).

     

    RETURN VALUES

    ntp_adjtime ();
    and ntp_gettime ();
    return the current state of the clock on success, or any of the errors of copyin(9) and copyout(9). ntp_adjtime ();
    may additionally return Er EPERM if the user calling ntp_adjtime ();
    does not have sufficient permissions.

    Possible states of the clock are:

    TIME_OK
    Everything okay, no leap second warning.
    TIME_INS
    ``insert leap second'' warning. At the end of the day, a leap second will be inserted after 23:59:59.
    TIME_DEL
    ``delete leap second'' warning. At the end of the day, second 23:59:59 will be skipped.
    TIME_OOP
    Leap second in progress.
    TIME_WAIT
    Leap second has occurred within the last few seconds..
    TIME_ERROR
    Clock not synchronized.

     

    ERRORS

    The ntp_adjtime ();
    system call may return Er EPERM if the caller does not have sufficient permissions.  

    SEE ALSO

    options(4), ntpd(8), hardclock(9), hz(9)

    http://www.bipm.fr/enus/5_Scientific/c_time/time_1.html
    http://www.boulder.nist.gov/timefreq/general/faq.htm
    ftp://time.nist.gov/pub/leap-seconds.list

     

    BUGS

    Take note that this API is extremely complex and stateful. Users should not attempt modification without first reviewing the ntpd(8) sources in depth.


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    ERRORS
    SEE ALSO
    BUGS


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