path: root/lib/libc/sys/ntp_adjtime.2

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.Dd July 13, 2005
.Dt NTP_ADJTIME 2
.Os
.Sh NAME
.Nm ntp_adjtime ,
.Nm ntp_gettime
.Nd Network Time Protocol (NTP) daemon interface system calls
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/timex.h
.Ft int
.Fn ntp_adjtime "struct timex *"
.Ft int
.Fn ntp_gettime "struct ntptimeval *"
.Sh DESCRIPTION
The two system calls
.Fn ntp_adjtime
and
.Fn ntp_gettime
are the kernel interface to the Network Time Protocol (NTP) daemon
.Xr ntpd 8 .
.Pp
The
.Fn 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
.Fn ntp_adjtime
are used by
.Fn hardclock
to adjust the phase and frequency of the phase- or frequency-lock loop
(PLL resp. FLL) which controls the system clock.
.Pp
The
.Fn ntp_gettime
function provides the time, maximum error (sync distance) and
estimated error (dispersion) to client user application programs.
.Pp
In the following, all variables that refer PPS are only relevant if
the
.Em PPS_SYNC
option is enabled in the kernel.
.Pp
.Fn ntp_adjtime
has as argument a
.Va struct timex *
of the following form:
.Bd -literal
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) */
};
.Ed
.Pp
The members of this struct have the following meanings when used as
argument for
.Fn ntp_adjtime :
.Bl -tag -width tolerance -compact
.It Fa modes
Defines what settings should be changed with the current
.Fn ntp_adjtime
call (write-only).
Bitwise OR of the following:
.Bl -tag -width MOD_TIMECONST -compact -offset indent
.It MOD_OFFSET
set time offset
.It MOD_FREQUENCY
set frequency offset
.It MOD_MAXERROR
set maximum time error
.It MOD_ESTERROR
set estimated time error
.It MOD_STATUS
set clock status bits
.It MOD_TIMECONST
set PLL time constant
.It MOD_CLKA
set clock A
.It MOD_CLKB
set clock B
.El
.It Fa offset
Time offset (in microseconds), used by the PLL/FLL to adjust the
system time in small increments (read-write).
.It Fa freq
Frequency offset (scaled ppm) (read-write).
.It Fa maxerror
Maximum error (in microseconds).
Initialized by an
.Fn ntp_adjtime
call, and increased by the kernel once each second to reflect the maximum
error bound growth (read-write).
.It Fa esterror
Estimated error (in microseconds).
Set and read by
.Fn ntp_adjtime ,
but unused by the kernel (read-write).
.It Fa status
System clock status bits (read-write).
Bitwise OR of the following:
.Bl -tag -width STA_PPSJITTER -compact -offset indent
.It STA_PLL
Enable PLL updates (read-write).
.It STA_PPSFREQ
Enable PPS freq discipline (read-write).
.It STA_PPSTIME
Enable PPS time discipline (read-write).
.It STA_FLL
Select frequency-lock mode (read-write).
.It STA_INS
Insert leap (read-write).
.It STA_DEL
Delete leap (read-write).
.It STA_UNSYNC
Clock unsynchronized (read-write).
.It STA_FREQHOLD
Hold frequency (read-write).
.It STA_PPSSIGNAL
PPS signal present (read-only).
.It STA_PPSJITTER
PPS signal jitter exceeded (read-only).
.It STA_PPSWANDER
PPS signal wander exceeded (read-only).
.It STA_PPSERROR
PPS signal calibration error (read-only).
.It STA_CLOCKERR
Clock hardware fault (read-only).
.El
.It Fa constant
PLL time constant, determines the bandwidth, or
.Dq stiffness ,
of the PLL (read-write).
.It Fa precision
Clock precision (in microseconds).
In most cases the same as the kernel tick variable (see
.Xr 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).
.It 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).
.It Fa ppsfreq
PPS frequency offset produced by the frequency median filter (scaled
ppm) (read-only).
.It Fa jitter
PPS jitter measured by the time median filter in microseconds
(read-only).
.It Fa shift
Logarithm to base 2 of the interval duration in seconds (PPS,
read-only).
.It Fa stabil
PPS stability (scaled ppm); dispersion (wander) measured by the
frequency median filter (read-only).
.It Fa jitcnt
Number of seconds that have been discarded because the jitter measured
by the time median filter exceeded the limit
.Em MAXTIME
(PPS, read-only).
.It Fa calcnt
Count of calibration intervals (PPS, read-only).
.It Fa errcnt
Number of calibration intervals that have been discarded because the
wander exceeded the limit
.Em MAXFREQ
or where the calibration interval jitter exceeded two ticks (PPS,
read-only).
.It Fa stbcnt
Number of calibration intervals that have been discarded because the
frequency wander exceeded the limit
.Em MAXFREQ Ns /4
(PPS, read-only).
.El
After the
.Fn ntp_adjtime
call, the
.Va struct timex *
structure contains the current values of the corresponding variables.
.Pp
.Fn ntp_gettime
has as argument a
.Va struct ntptimeval *
with the following members:
.Bd -literal
struct ntptimeval {
	struct timeval time;	/* current time (ro) */
	long maxerror;		/* maximum error (us) (ro) */
	long esterror;		/* estimated error (us) (ro) */
};
.Ed
.Pp
These have the following meaning:
.Bl -tag -width tolerance -compact
.It Fa time
Current time (read-only).
.It Fa maxerror
Maximum error in microseconds (read-only).
.It Fa esterror
Estimated error in microseconds (read-only).
.El
.Sh RETURN VALUES
.Fn ntp_adjtime
and
.Fn ntp_gettime
return the current state of the clock on success, or any of the errors
of
.Xr copyin 9
and
.Xr copyout 9 .
.Fn ntp_adjtime
may additionally return
.Er EPERM
if the user calling
.Fn ntp_adjtime
does not have sufficient permissions.
.Pp
Possible states of the clock are:
.Bl -tag -width TIME_ERROR -compact -offset indent
.It TIME_OK
Everything okay, no leap second warning.
.It TIME_INS
.Dq insert leap second
warning.
At the end of the day, a leap second will be inserted after 23:59:59.
.It TIME_DEL
.Dq delete leap second
warning.
At the end of the day, second 23:59:59 will be skipped.
.It TIME_OOP
Leap second in progress.
.It TIME_WAIT
Leap second has occurred within the last few seconds..
.It TIME_ERROR
Clock not synchronized.
.El
.Sh ERRORS
The
.Fn ntp_adjtime
system call may return
.Er EPERM
if the caller
does not have sufficient permissions.
.Sh SEE ALSO
.Xr options 4 ,
.Xr ntpd 8 ,
.Xr hardclock 9 ,
.Xr hz 9
.Bl -tag -width indent
.It Pa http://www.bipm.fr/enus/5_Scientific/c_time/time_1.html
.It Pa http://www.boulder.nist.gov/timefreq/general/faq.htm
.It Pa ftp://time.nist.gov/pub/leap-seconds.list
.El
.Sh BUGS
Take note that this
.Tn API
is extremely complex and stateful.
Users should not attempt modification without first
reviewing the
.Xr ntpd 8
sources in depth.