NTP_ADJTIME(2)

NAME
ntp_adjtime - NTP daemon application interface

SYNOPSIS
#include <sys/types.h>
#include <sys/timex.h>
int
ntp_adjtime(struct timex *tp);

DESCRIPTION
The ntp_adjtime() system call is used as a kernel interface for the Network Time Protocol daemon, ntpd(8). Certain fields of the timex structure are interpreted in either microseconds or nanoseconds, according to the state of the STA_NANO bit in the status word.

In the FreeBSD kernel, the ntp_adjtime() and ntp_gettime(2) system calls can be used to determine which resolution is in use, and to select either one at any time. The resolution selected affects the scaling of certain fields in the ntp_gettime() and ntp_adjtime() system calls.

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

    /*
     * NTP daemon interface (ntp_adjtime()) - used to discipline CPU clock
     * oscillator and determine status.
     *
     * Note: The offset, precision and jitter members are in microseconds if
     * STA_NANO is zero and nanoseconds if not.
     */
    struct timex {
    	unsigned int modes;	/* clock mode bits (wo) */
    	long	offset;		/* time offset (ns/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;	/* poll interval (log2 s) (rw) */
    	long	precision;	/* clock precision (ns/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. They are included in all configurations to insure
    	 * portability.
    	 */
    	long	ppsfreq;	/* PPS frequency (scaled PPM) (ro) */
    	long	jitter;		/* PPS jitter (ns/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) */
    };

Upon successful completion, ntp_adjtime() will fill the tp argument with the current clock state.

RETURN VALUES
Upon successful completion the clock state is returned. Otherwise a -1 is returned and the global variable errno is set to indicate the error.

Possible states of the clock are:

TIME_OK
    Everything okay, no leap second warning.
TIME_INS
    insert leap second warning.
TIME_DEL
    delete leap second warning.
TIME_OOP
    Leap second in progress.
TIME_WAIT
    Leap second has occurred.
TIME_ERROR
    Clock not synchronized.

ERRORS
The ntp_gettime() system call may return EPERM if the caller does not have sufficient permissions.

SEE ALSO
ntp_gettime(2), ntpd(8)

AUTHORS
This manual page was written by Tom Rhodes <trhodes@FreeBSD.org>.