7ec73f6417
Highlights:
* Simple model for underlying hardware.
* Hardware basis for timekeeping can be changed on the fly.
* Only one hardware clock responsible for TOD keeping.
* Provides a real nanotime() function.
* Time granularity: .232E-18 seconds.
* Frequency granularity: .238E-12 s/s
* Frequency adjustment is continuous in time.
* Less overhead for frequency adjustment.
* Improves xntpd performance.
Reviewed by: bde, bde, bde
812 lines
26 KiB
C
812 lines
26 KiB
C
/******************************************************************************
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* *
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* Copyright (c) David L. Mills 1993, 1994 *
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* *
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* Permission to use, copy, modify, and distribute this software and its *
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* documentation for any purpose and without fee is hereby granted, provided *
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* that the above copyright notice appears in all copies and that both the *
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* copyright notice and this permission notice appear in supporting *
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* documentation, and that the name University of Delaware not be used in *
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* advertising or publicity pertaining to distribution of the software *
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* without specific, written prior permission. The University of Delaware *
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* makes no representations about the suitability this software for any *
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* purpose. It is provided "as is" without express or implied warranty. *
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* *
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******************************************************************************/
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/*
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* Modification history kern_ntptime.c
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*
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* 24 Sep 94 David L. Mills
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* Tightened code at exits.
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*
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* 24 Mar 94 David L. Mills
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* Revised syscall interface to include new variables for PPS
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* time discipline.
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*
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* 14 Feb 94 David L. Mills
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* Added code for external clock
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*
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* 28 Nov 93 David L. Mills
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* Revised frequency scaling to conform with adjusted parameters
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*
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* 17 Sep 93 David L. Mills
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* Created file
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*/
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/*
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* ntp_gettime(), ntp_adjtime() - precision time interface for SunOS
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* V4.1.1 and V4.1.3
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*
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* These routines consitute the Network Time Protocol (NTP) interfaces
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* for user and daemon application programs. The ntp_gettime() routine
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* provides the time, maximum error (synch distance) and estimated error
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* (dispersion) to client user application programs. The ntp_adjtime()
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* routine is used by the NTP daemon to adjust the system clock to an
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* externally derived time. The time offset and related variables set by
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* this routine are used by hardclock() to adjust the phase and
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* frequency of the phase-lock loop which controls the system clock.
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*/
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#include "opt_ntp.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/sysproto.h>
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#include <sys/kernel.h>
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#include <sys/proc.h>
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#include <sys/timex.h>
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#include <sys/sysctl.h>
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/*
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* Phase/frequency-lock loop (PLL/FLL) definitions
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*
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* The following variables are read and set by the ntp_adjtime() system
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* call.
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*
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* time_state shows the state of the system clock, with values defined
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* in the timex.h header file.
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*
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* time_status shows the status of the system clock, with bits defined
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* in the timex.h header file.
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*
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* time_offset is used by the PLL/FLL to adjust the system time in small
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* increments.
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*
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* time_constant determines the bandwidth or "stiffness" of the PLL.
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*
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* time_tolerance determines maximum frequency error or tolerance of the
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* CPU clock oscillator and is a property of the architecture; however,
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* in principle it could change as result of the presence of external
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* discipline signals, for instance.
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*
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* time_precision is usually equal to the kernel tick variable; however,
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* in cases where a precision clock counter or external clock is
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* available, the resolution can be much less than this and depend on
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* whether the external clock is working or not.
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*
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* time_maxerror is initialized by a ntp_adjtime() call and increased by
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* the kernel once each second to reflect the maximum error
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* bound growth.
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*
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* time_esterror is set and read by the ntp_adjtime() call, but
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* otherwise not used by the kernel.
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*/
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static int time_status = STA_UNSYNC; /* clock status bits */
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static int time_state = TIME_OK; /* clock state */
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static long time_offset = 0; /* time offset (us) */
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static long time_constant = 0; /* pll time constant */
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static long time_tolerance = MAXFREQ; /* frequency tolerance (scaled ppm) */
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static long time_precision = 1; /* clock precision (us) */
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static long time_maxerror = MAXPHASE; /* maximum error (us) */
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static long time_esterror = MAXPHASE; /* estimated error (us) */
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static int time_daemon = 0; /* No timedaemon active */
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/*
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* The following variables establish the state of the PLL/FLL and the
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* residual time and frequency offset of the local clock. The scale
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* factors are defined in the timex.h header file.
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*
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* time_phase and time_freq are the phase increment and the frequency
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* increment, respectively, of the kernel time variable at each tick of
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* the clock.
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*
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* time_freq is set via ntp_adjtime() from a value stored in a file when
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* the synchronization daemon is first started. Its value is retrieved
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* via ntp_adjtime() and written to the file about once per hour by the
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* daemon.
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*
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* time_adj is the adjustment added to the value of tick at each timer
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* interrupt and is recomputed from time_phase and time_freq at each
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* seconds rollover.
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*
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* time_reftime is the second's portion of the system time on the last
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* call to ntp_adjtime(). It is used to adjust the time_freq variable
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* and to increase the time_maxerror as the time since last update
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* increases.
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*/
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long time_phase = 0; /* phase offset (scaled us) */
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static long time_freq = 0; /* frequency offset (scaled ppm) */
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long time_adj = 0; /* tick adjust (scaled 1 / hz) */
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static long time_reftime = 0; /* time at last adjustment (s) */
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#ifdef PPS_SYNC
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/*
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* The following variables are used only if the kernel PPS discipline
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* code is configured (PPS_SYNC). The scale factors are defined in the
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* timex.h header file.
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*
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* pps_time contains the time at each calibration interval, as read by
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* microtime(). pps_count counts the seconds of the calibration
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* interval, the duration of which is nominally pps_shift in powers of
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* two.
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*
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* pps_offset is the time offset produced by the time median filter
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* pps_tf[], while pps_jitter is the dispersion (jitter) measured by
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* this filter.
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*
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* pps_freq is the frequency offset produced by the frequency median
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* filter pps_ff[], while pps_stabil is the dispersion (wander) measured
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* by this filter.
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*
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* pps_usec is latched from a high resolution counter or external clock
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* at pps_time. Here we want the hardware counter contents only, not the
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* contents plus the time_tv.usec as usual.
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*
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* pps_valid counts the number of seconds since the last PPS update. It
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* is used as a watchdog timer to disable the PPS discipline should the
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* PPS signal be lost.
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*
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* pps_glitch counts the number of seconds since the beginning of an
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* offset burst more than tick/2 from current nominal offset. It is used
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* mainly to suppress error bursts due to priority conflicts between the
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* PPS interrupt and timer interrupt.
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*
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* pps_intcnt counts the calibration intervals for use in the interval-
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* adaptation algorithm. It's just too complicated for words.
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*/
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static struct timeval pps_time; /* kernel time at last interval */
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static long pps_offset = 0; /* pps time offset (us) */
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static long pps_jitter = MAXTIME; /* pps time dispersion (jitter) (us) */
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static long pps_tf[] = {0, 0, 0}; /* pps time offset median filter (us) */
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static long pps_freq = 0; /* frequency offset (scaled ppm) */
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static long pps_stabil = MAXFREQ; /* frequency dispersion (scaled ppm) */
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static long pps_ff[] = {0, 0, 0}; /* frequency offset median filter */
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static long pps_usec = 0; /* microsec counter at last interval */
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static long pps_valid = PPS_VALID; /* pps signal watchdog counter */
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static int pps_glitch = 0; /* pps signal glitch counter */
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static int pps_count = 0; /* calibration interval counter (s) */
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static int pps_shift = PPS_SHIFT; /* interval duration (s) (shift) */
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static int pps_intcnt = 0; /* intervals at current duration */
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/*
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* PPS signal quality monitors
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*
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* pps_jitcnt counts the seconds that have been discarded because the
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* jitter measured by the time median filter exceeds the limit MAXTIME
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* (100 us).
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*
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* pps_calcnt counts the frequency calibration intervals, which are
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* variable from 4 s to 256 s.
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*
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* pps_errcnt counts the calibration intervals which have been discarded
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* because the wander exceeds the limit MAXFREQ (100 ppm) or where the
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* calibration interval jitter exceeds two ticks.
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*
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* pps_stbcnt counts the calibration intervals that have been discarded
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* because the frequency wander exceeds the limit MAXFREQ / 4 (25 us).
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*/
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static long pps_jitcnt = 0; /* jitter limit exceeded */
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static long pps_calcnt = 0; /* calibration intervals */
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static long pps_errcnt = 0; /* calibration errors */
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static long pps_stbcnt = 0; /* stability limit exceeded */
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#endif /* PPS_SYNC */
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static void hardupdate __P((long offset));
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/*
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* hardupdate() - local clock update
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*
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* This routine is called by ntp_adjtime() to update the local clock
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* phase and frequency. The implementation is of an adaptive-parameter,
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* hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
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* time and frequency offset estimates for each call. If the kernel PPS
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* discipline code is configured (PPS_SYNC), the PPS signal itself
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* determines the new time offset, instead of the calling argument.
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* Presumably, calls to ntp_adjtime() occur only when the caller
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* believes the local clock is valid within some bound (+-128 ms with
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* NTP). If the caller's time is far different than the PPS time, an
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* argument will ensue, and it's not clear who will lose.
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*
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* For uncompensated quartz crystal oscillatores and nominal update
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* intervals less than 1024 s, operation should be in phase-lock mode
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* (STA_FLL = 0), where the loop is disciplined to phase. For update
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* intervals greater than thiss, operation should be in frequency-lock
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* mode (STA_FLL = 1), where the loop is disciplined to frequency.
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*
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* Note: splclock() is in effect.
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*/
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static void
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hardupdate(offset)
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long offset;
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{
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long ltemp, mtemp;
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if (!(time_status & STA_PLL) && !(time_status & STA_PPSTIME))
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return;
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ltemp = offset;
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#ifdef PPS_SYNC
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if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
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ltemp = pps_offset;
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#endif /* PPS_SYNC */
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/*
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* Scale the phase adjustment and clamp to the operating range.
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*/
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if (ltemp > MAXPHASE)
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time_offset = MAXPHASE << SHIFT_UPDATE;
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else if (ltemp < -MAXPHASE)
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time_offset = -(MAXPHASE << SHIFT_UPDATE);
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else
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time_offset = ltemp << SHIFT_UPDATE;
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/*
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* Select whether the frequency is to be controlled and in which
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* mode (PLL or FLL). Clamp to the operating range. Ugly
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* multiply/divide should be replaced someday.
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*/
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if (time_status & STA_FREQHOLD || time_reftime == 0)
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time_reftime = time.tv_sec;
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mtemp = time.tv_sec - time_reftime;
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time_reftime = time.tv_sec;
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if (time_status & STA_FLL) {
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if (mtemp >= MINSEC) {
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ltemp = ((time_offset / mtemp) << (SHIFT_USEC -
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SHIFT_UPDATE));
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if (ltemp < 0)
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time_freq -= -ltemp >> SHIFT_KH;
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else
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time_freq += ltemp >> SHIFT_KH;
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}
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} else {
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if (mtemp < MAXSEC) {
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ltemp *= mtemp;
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if (ltemp < 0)
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time_freq -= -ltemp >> (time_constant +
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time_constant + SHIFT_KF -
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SHIFT_USEC);
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else
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time_freq += ltemp >> (time_constant +
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time_constant + SHIFT_KF -
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SHIFT_USEC);
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}
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}
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if (time_freq > time_tolerance)
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time_freq = time_tolerance;
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else if (time_freq < -time_tolerance)
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time_freq = -time_tolerance;
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}
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/*
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* On rollover of the second the phase adjustment to be used for
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* the next second is calculated. Also, the maximum error is
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* increased by the tolerance. If the PPS frequency discipline
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* code is present, the phase is increased to compensate for the
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* CPU clock oscillator frequency error.
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*
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* On a 32-bit machine and given parameters in the timex.h
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* header file, the maximum phase adjustment is +-512 ms and
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* maximum frequency offset is a tad less than) +-512 ppm. On a
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* 64-bit machine, you shouldn't need to ask.
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*/
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void
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ntp_update_second(struct timecounter *tc)
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{
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u_int32_t *newsec;
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long ltemp;
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if (!time_daemon)
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return;
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newsec = &tc->offset_sec;
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time_maxerror += time_tolerance >> SHIFT_USEC;
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/*
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* Compute the phase adjustment for the next second. In
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* PLL mode, the offset is reduced by a fixed factor
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* times the time constant. In FLL mode the offset is
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* used directly. In either mode, the maximum phase
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* adjustment for each second is clamped so as to spread
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* the adjustment over not more than the number of
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* seconds between updates.
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*/
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if (time_offset < 0) {
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ltemp = -time_offset;
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if (!(time_status & STA_FLL))
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ltemp >>= SHIFT_KG + time_constant;
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if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
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ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE;
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time_offset += ltemp;
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time_adj = -ltemp << (SHIFT_SCALE - SHIFT_UPDATE);
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} else {
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ltemp = time_offset;
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if (!(time_status & STA_FLL))
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ltemp >>= SHIFT_KG + time_constant;
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if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
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ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE;
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time_offset -= ltemp;
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time_adj = ltemp << (SHIFT_SCALE - SHIFT_UPDATE);
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}
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/*
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* Compute the frequency estimate and additional phase
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* adjustment due to frequency error for the next
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* second. When the PPS signal is engaged, gnaw on the
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* watchdog counter and update the frequency computed by
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* the pll and the PPS signal.
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*/
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#ifdef PPS_SYNC
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pps_valid++;
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if (pps_valid == PPS_VALID) {
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pps_jitter = MAXTIME;
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pps_stabil = MAXFREQ;
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time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
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STA_PPSWANDER | STA_PPSERROR);
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}
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ltemp = time_freq + pps_freq;
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#else
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ltemp = time_freq;
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#endif /* PPS_SYNC */
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if (ltemp < 0)
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time_adj -= -ltemp << (SHIFT_SCALE - SHIFT_USEC);
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else
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time_adj += ltemp << (SHIFT_SCALE - SHIFT_USEC);
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tc->adjustment = time_adj;
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/* XXX - this is really bogus, but can't be fixed until
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xntpd's idea of the system clock is fixed to know how
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the user wants leap seconds handled; in the mean time,
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we assume that users of NTP are running without proper
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leap second support (this is now the default anyway) */
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/*
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* Leap second processing. If in leap-insert state at
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* the end of the day, the system clock is set back one
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* second; if in leap-delete state, the system clock is
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* set ahead one second. The microtime() routine or
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* external clock driver will insure that reported time
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* is always monotonic. The ugly divides should be
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* replaced.
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*/
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switch (time_state) {
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case TIME_OK:
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if (time_status & STA_INS)
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time_state = TIME_INS;
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else if (time_status & STA_DEL)
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time_state = TIME_DEL;
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break;
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case TIME_INS:
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if ((*newsec) % 86400 == 0) {
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(*newsec)--;
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time_state = TIME_OOP;
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}
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break;
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case TIME_DEL:
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if (((*newsec) + 1) % 86400 == 0) {
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(*newsec)++;
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time_state = TIME_WAIT;
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}
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break;
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case TIME_OOP:
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time_state = TIME_WAIT;
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break;
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case TIME_WAIT:
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if (!(time_status & (STA_INS | STA_DEL)))
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time_state = TIME_OK;
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break;
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}
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}
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static int
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ntp_sysctl SYSCTL_HANDLER_ARGS
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{
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struct timeval atv;
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struct ntptimeval ntv;
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int s;
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s = splclock();
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microtime(&atv);
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ntv.time = atv;
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ntv.maxerror = time_maxerror;
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ntv.esterror = time_esterror;
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splx(s);
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ntv.time_state = time_state;
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/*
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* Status word error decode. If any of these conditions
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* occur, an error is returned, instead of the status
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* word. Most applications will care only about the fact
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* the system clock may not be trusted, not about the
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* details.
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*
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* Hardware or software error
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*/
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if (time_status & (STA_UNSYNC | STA_CLOCKERR)) {
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ntv.time_state = TIME_ERROR;
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}
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/*
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* PPS signal lost when either time or frequency
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* synchronization requested
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*/
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if (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
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!(time_status & STA_PPSSIGNAL)) {
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ntv.time_state = TIME_ERROR;
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}
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/*
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* PPS jitter exceeded when time synchronization
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* requested
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*/
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if (time_status & STA_PPSTIME &&
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time_status & STA_PPSJITTER) {
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ntv.time_state = TIME_ERROR;
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}
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/*
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* PPS wander exceeded or calibration error when
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* frequency synchronization requested
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*/
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if (time_status & STA_PPSFREQ &&
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time_status & (STA_PPSWANDER | STA_PPSERROR)) {
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ntv.time_state = TIME_ERROR;
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}
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return (sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req));
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}
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SYSCTL_NODE(_kern, KERN_NTP_PLL, ntp_pll, CTLFLAG_RW, 0,
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"NTP kernel PLL related stuff");
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SYSCTL_PROC(_kern_ntp_pll, NTP_PLL_GETTIME, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD,
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0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", "");
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/*
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* ntp_adjtime() - NTP daemon application interface
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*/
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#ifndef _SYS_SYSPROTO_H_
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struct ntp_adjtime_args {
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struct timex *tp;
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};
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#endif
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int
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ntp_adjtime(struct proc *p, struct ntp_adjtime_args *uap)
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{
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struct timex ntv;
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int modes;
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int s;
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int error;
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time_daemon = 1;
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error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv));
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if (error)
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return error;
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/*
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* Update selected clock variables - only the superuser can
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* change anything. Note that there is no error checking here on
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* the assumption the superuser should know what it is doing.
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*/
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modes = ntv.modes;
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if ((modes != 0)
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&& (error = suser(p->p_cred->pc_ucred, &p->p_acflag)))
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return error;
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s = splclock();
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if (modes & MOD_FREQUENCY)
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#ifdef PPS_SYNC
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time_freq = ntv.freq - pps_freq;
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#else /* PPS_SYNC */
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time_freq = ntv.freq;
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#endif /* PPS_SYNC */
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if (modes & MOD_MAXERROR)
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time_maxerror = ntv.maxerror;
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if (modes & MOD_ESTERROR)
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time_esterror = ntv.esterror;
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if (modes & MOD_STATUS) {
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time_status &= STA_RONLY;
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time_status |= ntv.status & ~STA_RONLY;
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}
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if (modes & MOD_TIMECONST)
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time_constant = ntv.constant;
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if (modes & MOD_OFFSET)
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hardupdate(ntv.offset);
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/*
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* Retrieve all clock variables
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*/
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if (time_offset < 0)
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ntv.offset = -(-time_offset >> SHIFT_UPDATE);
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else
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ntv.offset = time_offset >> SHIFT_UPDATE;
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#ifdef PPS_SYNC
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ntv.freq = time_freq + pps_freq;
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#else /* PPS_SYNC */
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ntv.freq = time_freq;
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#endif /* PPS_SYNC */
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ntv.maxerror = time_maxerror;
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ntv.esterror = time_esterror;
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ntv.status = time_status;
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ntv.constant = time_constant;
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ntv.precision = time_precision;
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ntv.tolerance = time_tolerance;
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#ifdef PPS_SYNC
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ntv.shift = pps_shift;
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ntv.ppsfreq = pps_freq;
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ntv.jitter = pps_jitter >> PPS_AVG;
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ntv.stabil = pps_stabil;
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ntv.calcnt = pps_calcnt;
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ntv.errcnt = pps_errcnt;
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ntv.jitcnt = pps_jitcnt;
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ntv.stbcnt = pps_stbcnt;
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#endif /* PPS_SYNC */
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(void)splx(s);
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error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv));
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if (!error) {
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/*
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* Status word error decode. See comments in
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* ntp_gettime() routine.
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*/
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p->p_retval[0] = time_state;
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if (time_status & (STA_UNSYNC | STA_CLOCKERR))
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p->p_retval[0] = TIME_ERROR;
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if (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
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!(time_status & STA_PPSSIGNAL))
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p->p_retval[0] = TIME_ERROR;
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if (time_status & STA_PPSTIME &&
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time_status & STA_PPSJITTER)
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p->p_retval[0] = TIME_ERROR;
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if (time_status & STA_PPSFREQ &&
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time_status & (STA_PPSWANDER | STA_PPSERROR))
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p->p_retval[0] = TIME_ERROR;
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}
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return error;
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}
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#ifdef PPS_SYNC
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/* We need this ugly monster twice, so let's macroize it. */
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#define MEDIAN3X(a, m, s, i1, i2, i3) \
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do { \
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m = a[i2]; \
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s = a[i1] - a[i3]; \
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} while (0)
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#define MEDIAN3(a, m, s) \
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do { \
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if (a[0] > a[1]) { \
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if (a[1] > a[2]) \
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MEDIAN3X(a, m, s, 0, 1, 2); \
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else if (a[2] > a[0]) \
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MEDIAN3X(a, m, s, 2, 0, 1); \
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else \
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MEDIAN3X(a, m, s, 0, 2, 1); \
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} else { \
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if (a[2] > a[1]) \
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MEDIAN3X(a, m, s, 2, 1, 0); \
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else if (a[0] > a[2]) \
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MEDIAN3X(a, m, s, 1, 0, 2); \
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else \
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MEDIAN3X(a, m, s, 1, 2, 0); \
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} \
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} while (0)
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/*
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* hardpps() - discipline CPU clock oscillator to external PPS signal
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*
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* This routine is called at each PPS interrupt in order to discipline
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* the CPU clock oscillator to the PPS signal. It measures the PPS phase
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* and leaves it in a handy spot for the hardclock() routine. It
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* integrates successive PPS phase differences and calculates the
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* frequency offset. This is used in hardclock() to discipline the CPU
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* clock oscillator so that intrinsic frequency error is cancelled out.
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* The code requires the caller to capture the time and hardware counter
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* value at the on-time PPS signal transition.
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*
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* Note that, on some Unix systems, this routine runs at an interrupt
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* priority level higher than the timer interrupt routine hardclock().
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* Therefore, the variables used are distinct from the hardclock()
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* variables, except for certain exceptions: The PPS frequency pps_freq
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* and phase pps_offset variables are determined by this routine and
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* updated atomically. The time_tolerance variable can be considered a
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* constant, since it is infrequently changed, and then only when the
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* PPS signal is disabled. The watchdog counter pps_valid is updated
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* once per second by hardclock() and is atomically cleared in this
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* routine.
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*/
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void
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hardpps(tvp, p_usec)
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struct timeval *tvp; /* time at PPS */
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long p_usec; /* hardware counter at PPS */
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{
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long u_usec, v_usec, bigtick;
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long cal_sec, cal_usec;
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/*
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* An occasional glitch can be produced when the PPS interrupt
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* occurs in the hardclock() routine before the time variable is
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* updated. Here the offset is discarded when the difference
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* between it and the last one is greater than tick/2, but not
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* if the interval since the first discard exceeds 30 s.
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*/
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time_status |= STA_PPSSIGNAL;
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time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
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pps_valid = 0;
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u_usec = -tvp->tv_usec;
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if (u_usec < -500000)
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u_usec += 1000000;
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v_usec = pps_offset - u_usec;
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if (v_usec < 0)
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v_usec = -v_usec;
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if (v_usec > (tick >> 1)) {
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if (pps_glitch > MAXGLITCH) {
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pps_glitch = 0;
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pps_tf[2] = u_usec;
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pps_tf[1] = u_usec;
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} else {
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pps_glitch++;
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u_usec = pps_offset;
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}
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} else
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pps_glitch = 0;
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/*
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* A three-stage median filter is used to help deglitch the pps
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* time. The median sample becomes the time offset estimate; the
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* difference between the other two samples becomes the time
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* dispersion (jitter) estimate.
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*/
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pps_tf[2] = pps_tf[1];
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pps_tf[1] = pps_tf[0];
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pps_tf[0] = u_usec;
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MEDIAN3(pps_tf, pps_offset, v_usec);
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if (v_usec > MAXTIME)
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pps_jitcnt++;
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v_usec = (v_usec << PPS_AVG) - pps_jitter;
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if (v_usec < 0)
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pps_jitter -= -v_usec >> PPS_AVG;
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else
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pps_jitter += v_usec >> PPS_AVG;
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if (pps_jitter > (MAXTIME >> 1))
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time_status |= STA_PPSJITTER;
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/*
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* During the calibration interval adjust the starting time when
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* the tick overflows. At the end of the interval compute the
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* duration of the interval and the difference of the hardware
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* counters at the beginning and end of the interval. This code
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* is deliciously complicated by the fact valid differences may
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* exceed the value of tick when using long calibration
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* intervals and small ticks. Note that the counter can be
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* greater than tick if caught at just the wrong instant, but
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* the values returned and used here are correct.
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*/
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bigtick = (long)tick << SHIFT_USEC;
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pps_usec -= pps_freq;
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if (pps_usec >= bigtick)
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pps_usec -= bigtick;
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if (pps_usec < 0)
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pps_usec += bigtick;
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pps_time.tv_sec++;
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pps_count++;
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if (pps_count < (1 << pps_shift))
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return;
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pps_count = 0;
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pps_calcnt++;
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u_usec = p_usec << SHIFT_USEC;
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v_usec = pps_usec - u_usec;
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if (v_usec >= bigtick >> 1)
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v_usec -= bigtick;
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if (v_usec < -(bigtick >> 1))
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v_usec += bigtick;
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if (v_usec < 0)
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v_usec = -(-v_usec >> pps_shift);
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else
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v_usec = v_usec >> pps_shift;
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pps_usec = u_usec;
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cal_sec = tvp->tv_sec;
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cal_usec = tvp->tv_usec;
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cal_sec -= pps_time.tv_sec;
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cal_usec -= pps_time.tv_usec;
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if (cal_usec < 0) {
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cal_usec += 1000000;
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cal_sec--;
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}
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pps_time = *tvp;
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/*
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* Check for lost interrupts, noise, excessive jitter and
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* excessive frequency error. The number of timer ticks during
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* the interval may vary +-1 tick. Add to this a margin of one
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* tick for the PPS signal jitter and maximum frequency
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* deviation. If the limits are exceeded, the calibration
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* interval is reset to the minimum and we start over.
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*/
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u_usec = (long)tick << 1;
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if (!((cal_sec == -1 && cal_usec > (1000000 - u_usec))
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|| (cal_sec == 0 && cal_usec < u_usec))
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|| v_usec > time_tolerance || v_usec < -time_tolerance) {
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pps_errcnt++;
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pps_shift = PPS_SHIFT;
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pps_intcnt = 0;
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time_status |= STA_PPSERROR;
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return;
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}
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/*
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* A three-stage median filter is used to help deglitch the pps
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* frequency. The median sample becomes the frequency offset
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* estimate; the difference between the other two samples
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* becomes the frequency dispersion (stability) estimate.
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*/
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pps_ff[2] = pps_ff[1];
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pps_ff[1] = pps_ff[0];
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pps_ff[0] = v_usec;
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MEDIAN3(pps_ff, u_usec, v_usec);
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/*
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* Here the frequency dispersion (stability) is updated. If it
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* is less than one-fourth the maximum (MAXFREQ), the frequency
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* offset is updated as well, but clamped to the tolerance. It
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* will be processed later by the hardclock() routine.
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*/
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v_usec = (v_usec >> 1) - pps_stabil;
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if (v_usec < 0)
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pps_stabil -= -v_usec >> PPS_AVG;
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else
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pps_stabil += v_usec >> PPS_AVG;
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if (pps_stabil > MAXFREQ >> 2) {
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pps_stbcnt++;
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time_status |= STA_PPSWANDER;
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return;
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}
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if (time_status & STA_PPSFREQ) {
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if (u_usec < 0) {
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pps_freq -= -u_usec >> PPS_AVG;
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if (pps_freq < -time_tolerance)
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pps_freq = -time_tolerance;
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u_usec = -u_usec;
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} else {
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pps_freq += u_usec >> PPS_AVG;
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if (pps_freq > time_tolerance)
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pps_freq = time_tolerance;
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}
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}
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/*
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* Here the calibration interval is adjusted. If the maximum
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* time difference is greater than tick / 4, reduce the interval
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* by half. If this is not the case for four consecutive
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* intervals, double the interval.
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*/
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if (u_usec << pps_shift > bigtick >> 2) {
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pps_intcnt = 0;
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if (pps_shift > PPS_SHIFT)
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pps_shift--;
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} else if (pps_intcnt >= 4) {
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pps_intcnt = 0;
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if (pps_shift < PPS_SHIFTMAX)
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pps_shift++;
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} else
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pps_intcnt++;
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}
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#endif /* PPS_SYNC */
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