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freebsd/sys/kern/kern_ntptime.c
Poul-Henning Kamp 5968e18b69 pps_shiftmax only exists #ifdef PPS_SYNC 
Found by:	Roger Hardiman <roger@cs.strath.ac.uk>
1999-08-30 16:21:32 +00:00

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/***********************************************************************
* *
* Copyright (c) David L. Mills 1993-1999 *
* *
* Permission to use, copy, modify, and distribute this software and *
* its documentation for any purpose and without fee is hereby *
* granted, provided that the above copyright notice appears in all *
* copies and that both the copyright notice and this permission *
* notice appear in supporting documentation, and that the name *
* University of Delaware not be used in advertising or publicity *
* pertaining to distribution of the software without specific, *
* written prior permission. The University of Delaware makes no *
* representations about the suitability this software for any *
* purpose. It is provided "as is" without express or implied *
* warranty. *
* *
**********************************************************************/
/*
* Adapted from the original sources for FreeBSD and timecounters by:
* Poul-Henning Kamp <phk@FreeBSD.org>.
*
* The 32bit version of the "LP" macros seems a bit past its "sell by"
* date so I have retained only the 64bit version and included it directly
* in this file.
*
* Only minor changes done to interface with the timecounters over in
* sys/kern/kern_clock.c. Some of the comments below may be (even more)
* confusing and/or plain wrong in that context.
*/
#include "opt_ntp.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/time.h>
#include <sys/timex.h>
#include <sys/timepps.h>
#include <sys/sysctl.h>
/*
* Single-precision macros for 64-bit machines
*/
typedef long long l_fp;
#define L_ADD(v, u) ((v) += (u))
#define L_SUB(v, u) ((v) -= (u))
#define L_ADDHI(v, a) ((v) += (long long)(a) << 32)
#define L_NEG(v) ((v) = -(v))
#define L_RSHIFT(v, n) \
do { \
if ((v) < 0) \
(v) = -(-(v) >> (n)); \
else \
(v) = (v) >> (n); \
} while (0)
#define L_MPY(v, a) ((v) *= (a))
#define L_CLR(v) ((v) = 0)
#define L_ISNEG(v) ((v) < 0)
#define L_LINT(v, a) ((v) = (long long)(a) << 32)
#define L_GINT(v) ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)
/*
* Generic NTP kernel interface
*
* These routines constitute the Network Time Protocol (NTP) interfaces
* for user and daemon application programs. The ntp_gettime() routine
* provides the time, maximum error (synch distance) and estimated error
* (dispersion) to client user application programs. The ntp_adjtime()
* routine is used by the NTP daemon to adjust the system clock to an
* externally derived time. The time offset and related variables set by
* this routine are used by other routines in this module to adjust the
* phase and frequency of the clock discipline loop which controls the
* system clock.
*
* When the kernel time is reckoned directly in nanoseconds (NTP_NANO
* defined), the time at each tick interrupt is derived directly from
* the kernel time variable. When the kernel time is reckoned in
* microseconds, (NTP_NANO undefined), the time is derived from the
* kernel time variable together with a variable representing the
* leftover nanoseconds at the last tick interrupt. In either case, the
* current nanosecond time is reckoned from these values plus an
* interpolated value derived by the clock routines in another
* architecture-specific module. The interpolation can use either a
* dedicated counter or a processor cycle counter (PCC) implemented in
* some architectures.
*
* Note that all routines must run at priority splclock or higher.
*/
/*
* Phase/frequency-lock loop (PLL/FLL) definitions
*
* The nanosecond clock discipline uses two variable types, time
* variables and frequency variables. Both types are represented as 64-
* bit fixed-point quantities with the decimal point between two 32-bit
* halves. On a 32-bit machine, each half is represented as a single
* word and mathematical operations are done using multiple-precision
* arithmetic. On a 64-bit machine, ordinary computer arithmetic is
* used.
*
* A time variable is a signed 64-bit fixed-point number in ns and
* fraction. It represents the remaining time offset to be amortized
* over succeeding tick interrupts. The maximum time offset is about
* 0.5 s and the resolution is about 2.3e-10 ns.
*
* 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* |s s s| ns |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | fraction |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*
* A frequency variable is a signed 64-bit fixed-point number in ns/s
* and fraction. It represents the ns and fraction to be added to the
* kernel time variable at each second. The maximum frequency offset is
* about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
*
* 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* |s s s s s s s s s s s s s| ns/s |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | fraction |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
/*
* The following variables establish the state of the PLL/FLL and the
* residual time and frequency offset of the local clock.
*/
#define SHIFT_PLL 4 /* PLL loop gain (shift) */
#define SHIFT_FLL 2 /* FLL loop gain (shift) */
static int time_state = TIME_OK; /* clock state */
static int time_status = STA_UNSYNC; /* clock status bits */
static long time_constant; /* poll interval (shift) (s) */
static long time_precision = 1; /* clock precision (ns) */
static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */
static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */
static long time_reftime; /* time at last adjustment (s) */
static long time_tick; /* nanoseconds per tick (ns) */
static l_fp time_offset; /* time offset (ns) */
static l_fp time_freq; /* frequency offset (ns/s) */
#ifdef PPS_SYNC
/*
* The following variables are used when a pulse-per-second (PPS) signal
* is available and connected via a modem control lead. They establish
* the engineering parameters of the clock discipline loop when
* controlled by the PPS signal.
*/
#define PPS_FAVG 2 /* min freq avg interval (s) (shift) */
#define PPS_FAVGDEF 7 /* default freq avg int (s) (shift) */
#define PPS_FAVGMAX 15 /* max freq avg interval (s) (shift) */
#define PPS_PAVG 4 /* phase avg interval (s) (shift) */
#define PPS_VALID 120 /* PPS signal watchdog max (s) */
#define PPS_MAXWANDER 100000 /* max PPS wander (ns/s) */
#define PPS_POPCORN 2 /* popcorn spike threshold (shift) */
static struct timespec pps_tf[3]; /* phase median filter */
static l_fp pps_freq; /* scaled frequency offset (ns/s) */
static long pps_fcount; /* frequency accumulator */
static long pps_jitter; /* nominal jitter (ns) */
static long pps_stabil; /* nominal stability (scaled ns/s) */
static long pps_lastsec; /* time at last calibration (s) */
static int pps_valid; /* signal watchdog counter */
static int pps_shift = PPS_FAVG; /* interval duration (s) (shift) */
static int pps_shiftmax = PPS_FAVGDEF; /* max interval duration (s) (shift) */
static int pps_intcnt; /* wander counter */
/*
* PPS signal quality monitors
*/
static long pps_calcnt; /* calibration intervals */
static long pps_jitcnt; /* jitter limit exceeded */
static long pps_stbcnt; /* stability limit exceeded */
static long pps_errcnt; /* calibration errors */
#endif /* PPS_SYNC */
/*
* End of phase/frequency-lock loop (PLL/FLL) definitions
*/
static void ntp_init(void);
static void hardupdate(long offset);
/*
* ntp_gettime() - NTP user application interface
*
* See the timex.h header file for synopsis and API description.
*/
static int
ntp_sysctl SYSCTL_HANDLER_ARGS
{
struct ntptimeval ntv; /* temporary structure */
struct timespec atv; /* nanosecond time */
nanotime(&atv);
ntv.time.tv_sec = atv.tv_sec;
ntv.time.tv_nsec = atv.tv_nsec;
ntv.maxerror = time_maxerror;
ntv.esterror = time_esterror;
ntv.time_state = time_state;
/*
* Status word error decode. If any of these conditions occur,
* an error is returned, instead of the status word. Most
* applications will care only about the fact the system clock
* may not be trusted, not about the details.
*
* Hardware or software error
*/
if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
/*
* PPS signal lost when either time or frequency synchronization
* requested
*/
(time_status & (STA_PPSFREQ | STA_PPSTIME) &&
!(time_status & STA_PPSSIGNAL)) ||
/*
* PPS jitter exceeded when time synchronization requested
*/
(time_status & STA_PPSTIME &&
time_status & STA_PPSJITTER) ||
/*
* PPS wander exceeded or calibration error when frequency
* synchronization requested
*/
(time_status & STA_PPSFREQ &&
time_status & (STA_PPSWANDER | STA_PPSERROR)))
ntv.time_state = TIME_ERROR;
return (sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req));
}
SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, "");
SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD,
0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", "");
#ifdef PPS_SYNC
SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RW, &pps_shiftmax, 0, "");
#endif
/*
* ntp_adjtime() - NTP daemon application interface
*
* See the timex.h header file for synopsis and API description.
*/
#ifndef _SYS_SYSPROTO_H_
struct ntp_adjtime_args {
struct timex *tp;
};
#endif
int
ntp_adjtime(struct proc *p, struct ntp_adjtime_args *uap)
{
struct timex ntv; /* temporary structure */
long freq; /* frequency ns/s) */
int modes; /* mode bits from structure */
int s; /* caller priority */
int error;
error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv));
if (error)
return(error);
/*
* Update selected clock variables - only the superuser can
* change anything. Note that there is no error checking here on
* the assumption the superuser should know what it is doing.
*/
modes = ntv.modes;
if (modes)
error = suser(p);
if (error)
return (error);
s = splclock();
if (modes & MOD_FREQUENCY) {
freq = (ntv.freq * 1000LL) >> 16;
if (freq > MAXFREQ)
L_LINT(time_freq, MAXFREQ);
else if (freq < -MAXFREQ)
L_LINT(time_freq, -MAXFREQ);
else
L_LINT(time_freq, freq);
#ifdef PPS_SYNC
pps_freq = time_freq;
#endif /* PPS_SYNC */
}
if (modes & MOD_MAXERROR)
time_maxerror = ntv.maxerror;
if (modes & MOD_ESTERROR)
time_esterror = ntv.esterror;
if (modes & MOD_STATUS) {
time_status &= STA_RONLY;
time_status |= ntv.status & ~STA_RONLY;
}
if (modes & MOD_TIMECONST) {
if (ntv.constant < 0)
time_constant = 0;
else if (ntv.constant > MAXTC)
time_constant = MAXTC;
else
time_constant = ntv.constant;
}
#ifdef PPS_SYNC
if (modes & MOD_PPSMAX) {
if (ntv.shift < PPS_FAVG)
pps_shiftmax = PPS_FAVG;
else if (ntv.shift > PPS_FAVGMAX)
pps_shiftmax = PPS_FAVGMAX;
else
pps_shiftmax = ntv.shift;
}
#endif /* PPS_SYNC */
if (modes & MOD_NANO)
time_status |= STA_NANO;
if (modes & MOD_MICRO)
time_status &= ~STA_NANO;
if (modes & MOD_CLKB)
time_status |= STA_CLK;
if (modes & MOD_CLKA)
time_status &= ~STA_CLK;
if (modes & MOD_OFFSET) {
if (time_status & STA_NANO)
hardupdate(ntv.offset);
else
hardupdate(ntv.offset * 1000);
}
/*
* Retrieve all clock variables
*/
if (time_status & STA_NANO)
ntv.offset = L_GINT(time_offset);
else
ntv.offset = L_GINT(time_offset) / 1000;
ntv.freq = L_GINT((time_freq / 1000LL) << 16);
ntv.maxerror = time_maxerror;
ntv.esterror = time_esterror;
ntv.status = time_status;
ntv.constant = time_constant;
if (time_status & STA_NANO)
ntv.precision = time_precision;
else
ntv.precision = time_precision / 1000;
ntv.tolerance = MAXFREQ * SCALE_PPM;
#ifdef PPS_SYNC
ntv.shift = pps_shift;
ntv.ppsfreq = L_GINT((pps_freq / 1000LL) << 16);
if (time_status & STA_NANO)
ntv.jitter = pps_jitter;
else
ntv.jitter = pps_jitter / 1000;
ntv.stabil = pps_stabil;
ntv.calcnt = pps_calcnt;
ntv.errcnt = pps_errcnt;
ntv.jitcnt = pps_jitcnt;
ntv.stbcnt = pps_stbcnt;
#endif /* PPS_SYNC */
splx(s);
error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv));
if (error)
return (error);
/*
* Status word error decode. See comments in
* ntp_gettime() routine.
*/
if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
(time_status & (STA_PPSFREQ | STA_PPSTIME) &&
!(time_status & STA_PPSSIGNAL)) ||
(time_status & STA_PPSTIME &&
time_status & STA_PPSJITTER) ||
(time_status & STA_PPSFREQ &&
time_status & (STA_PPSWANDER | STA_PPSERROR)))
p->p_retval[0] = TIME_ERROR;
else
p->p_retval[0] = time_state;
return (error);
}
/*
* second_overflow() - called after ntp_tick_adjust()
*
* This routine is ordinarily called immediately following the above
* routine ntp_tick_adjust(). While these two routines are normally
* combined, they are separated here only for the purposes of
* simulation.
*/
void
ntp_update_second(struct timecounter *tcp)
{
u_int32_t *newsec;
l_fp ftemp, time_adj; /* 32/64-bit temporaries */
newsec = &tcp->tc_offset_sec;
/*
* On rollover of the second both the nanosecond and microsecond
* clocks are updated and the state machine cranked as
* necessary. The phase adjustment to be used for the next
* second is calculated and the maximum error is increased by
* the tolerance.
*/
time_maxerror += MAXFREQ / 1000;
/*
* Leap second processing. If in leap-insert state at
* the end of the day, the system clock is set back one
* second; if in leap-delete state, the system clock is
* set ahead one second. The nano_time() routine or
* external clock driver will insure that reported time
* is always monotonic.
*/
switch (time_state) {
/*
* No warning.
*/
case TIME_OK:
if (time_status & STA_INS)
time_state = TIME_INS;
else if (time_status & STA_DEL)
time_state = TIME_DEL;
break;
/*
* Insert second 23:59:60 following second
* 23:59:59.
*/
case TIME_INS:
if (!(time_status & STA_INS))
time_state = TIME_OK;
else if ((*newsec) % 86400 == 0) {
(*newsec)--;
time_state = TIME_OOP;
}
break;
/*
* Delete second 23:59:59.
*/
case TIME_DEL:
if (!(time_status & STA_DEL))
time_state = TIME_OK;
else if (((*newsec) + 1) % 86400 == 0) {
(*newsec)++;
time_state = TIME_WAIT;
}
break;
/*
* Insert second in progress.
*/
case TIME_OOP:
time_state = TIME_WAIT;
break;
/*
* Wait for status bits to clear.
*/
case TIME_WAIT:
if (!(time_status & (STA_INS | STA_DEL)))
time_state = TIME_OK;
}
/*
* Compute the total time adjustment for the next second
* in ns. The offset is reduced by a factor depending on
* whether the PPS signal is operating. Note that the
* value is in effect scaled by the clock frequency,
* since the adjustment is added at each tick interrupt.
*/
ftemp = time_offset;
#ifdef PPS_SYNC
if (time_status & STA_PPSTIME && time_status &
STA_PPSSIGNAL)
L_RSHIFT(ftemp, PPS_FAVG);
else
L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
#else
L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
#endif /* PPS_SYNC */
time_adj = ftemp;
L_SUB(time_offset, ftemp);
L_ADD(time_adj, time_freq);
tcp->tc_adjustment = time_adj;
#ifdef PPS_SYNC
if (pps_valid > 0)
pps_valid--;
else
time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
STA_PPSWANDER | STA_PPSERROR);
#endif /* PPS_SYNC */
}
/*
* ntp_init() - initialize variables and structures
*
* This routine must be called after the kernel variables hz and tick
* are set or changed and before the next tick interrupt. In this
* particular implementation, these values are assumed set elsewhere in
* the kernel. The design allows the clock frequency and tick interval
* to be changed while the system is running. So, this routine should
* probably be integrated with the code that does that.
*/
static void
ntp_init()
{
/*
* The following variable must be initialized any time the
* kernel variable hz is changed.
*/
time_tick = NANOSECOND / hz;
/*
* The following variables are initialized only at startup. Only
* those structures not cleared by the compiler need to be
* initialized, and these only in the simulator. In the actual
* kernel, any nonzero values here will quickly evaporate.
*/
L_CLR(time_offset);
L_CLR(time_freq);
#ifdef PPS_SYNC
pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0;
pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0;
pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0;
pps_fcount = 0;
L_CLR(pps_freq);
#endif /* PPS_SYNC */
}
SYSINIT(ntpclocks, SI_SUB_CLOCKS, SI_ORDER_FIRST, ntp_init, NULL)
/*
* hardupdate() - local clock update
*
* This routine is called by ntp_adjtime() to update the local clock
* phase and frequency. The implementation is of an adaptive-parameter,
* hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
* time and frequency offset estimates for each call. If the kernel PPS
* discipline code is configured (PPS_SYNC), the PPS signal itself
* determines the new time offset, instead of the calling argument.
* Presumably, calls to ntp_adjtime() occur only when the caller
* believes the local clock is valid within some bound (+-128 ms with
* NTP). If the caller's time is far different than the PPS time, an
* argument will ensue, and it's not clear who will lose.
*
* For uncompensated quartz crystal oscillators and nominal update
* intervals less than 256 s, operation should be in phase-lock mode,
* where the loop is disciplined to phase. For update intervals greater
* than 1024 s, operation should be in frequency-lock mode, where the
* loop is disciplined to frequency. Between 256 s and 1024 s, the mode
* is selected by the STA_MODE status bit.
*/
static void
hardupdate(offset)
long offset; /* clock offset (ns) */
{
long ltemp, mtemp;
l_fp ftemp;
/*
* Select how the phase is to be controlled and from which
* source. If the PPS signal is present and enabled to
* discipline the time, the PPS offset is used; otherwise, the
* argument offset is used.
*/
if (!(time_status & STA_PLL))
return;
ltemp = offset;
if (ltemp > MAXPHASE)
ltemp = MAXPHASE;
else if (ltemp < -MAXPHASE)
ltemp = -MAXPHASE;
if (!(time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL))
L_LINT(time_offset, ltemp);
/*
* Select how the frequency is to be controlled and in which
* mode (PLL or FLL). If the PPS signal is present and enabled
* to discipline the frequency, the PPS frequency is used;
* otherwise, the argument offset is used to compute it.
*/
if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) {
time_reftime = time_second;
return;
}
if (time_status & STA_FREQHOLD || time_reftime == 0)
time_reftime = time_second;
mtemp = time_second - time_reftime;
L_LINT(ftemp, ltemp);
L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1);
L_MPY(ftemp, mtemp);
L_ADD(time_freq, ftemp);
time_status &= ~STA_MODE;
if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
L_LINT(ftemp, (ltemp << 4) / mtemp);
L_RSHIFT(ftemp, SHIFT_FLL + 4);
L_ADD(time_freq, ftemp);
time_status |= STA_MODE;
}
time_reftime = time_second;
if (L_GINT(time_freq) > MAXFREQ)
L_LINT(time_freq, MAXFREQ);
else if (L_GINT(time_freq) < -MAXFREQ)
L_LINT(time_freq, -MAXFREQ);
}
#ifdef PPS_SYNC
/*
* hardpps() - discipline CPU clock oscillator to external PPS signal
*
* This routine is called at each PPS interrupt in order to discipline
* the CPU clock oscillator to the PPS signal. It measures the PPS phase
* and leaves it in a handy spot for the hardclock() routine. It
* integrates successive PPS phase differences and calculates the
* frequency offset. This is used in hardclock() to discipline the CPU
* clock oscillator so that the intrinsic frequency error is cancelled
* out. The code requires the caller to capture the time and
* architecture-dependent hardware counter values in nanoseconds at the
* on-time PPS signal transition.
*
* Note that, on some Unix systems this routine runs at an interrupt
* priority level higher than the timer interrupt routine hardclock().
* Therefore, the variables used are distinct from the hardclock()
* variables, except for the actual time and frequency variables, which
* are determined by this routine and updated atomically.
*/
void
hardpps(tsp, nsec)
struct timespec *tsp; /* time at PPS */
long nsec; /* hardware counter at PPS */
{
long u_sec, u_nsec, v_nsec; /* temps */
l_fp ftemp;
/*
* The signal is first processed by a frequency discriminator
* which rejects noise and input signals with frequencies
* outside the range 1 +-MAXFREQ PPS. If two hits occur in the
* same second, we ignore the later hit; if not and a hit occurs
* outside the range gate, keep the later hit but do not
* process it.
*/
time_status |= STA_PPSSIGNAL | STA_PPSJITTER;
time_status &= ~(STA_PPSWANDER | STA_PPSERROR);
pps_valid = PPS_VALID;
u_sec = tsp->tv_sec;
u_nsec = tsp->tv_nsec;
if (u_nsec >= (NANOSECOND >> 1)) {
u_nsec -= NANOSECOND;
u_sec++;
}
v_nsec = u_nsec - pps_tf[0].tv_nsec;
if (u_sec == pps_tf[0].tv_sec && v_nsec < -MAXFREQ) {
return;
}
pps_tf[2] = pps_tf[1];
pps_tf[1] = pps_tf[0];
pps_tf[0].tv_sec = u_sec;
pps_tf[0].tv_nsec = u_nsec;
/*
* Compute the difference between the current and previous
* counter values. If the difference exceeds 0.5 s, assume it
* has wrapped around, so correct 1.0 s. If the result exceeds
* the tick interval, the sample point has crossed a tick
* boundary during the last second, so correct the tick. Very
* intricate.
*/
u_nsec = nsec;
if (u_nsec > (NANOSECOND >> 1))
u_nsec -= NANOSECOND;
else if (u_nsec < -(NANOSECOND >> 1))
u_nsec += NANOSECOND;
pps_fcount += u_nsec;
if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ) {
return;
}
time_status &= ~STA_PPSJITTER;
/*
* A three-stage median filter is used to help denoise the PPS
* time. The median sample becomes the time offset estimate; the
* difference between the other two samples becomes the time
* dispersion (jitter) estimate.
*/
if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) {
if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) {
v_nsec = pps_tf[1].tv_nsec; /* 0 1 2 */
u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec;
} else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) {
v_nsec = pps_tf[0].tv_nsec; /* 2 0 1 */
u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec;
} else {
v_nsec = pps_tf[2].tv_nsec; /* 0 2 1 */
u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec;
}
} else {
if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) {
v_nsec = pps_tf[1].tv_nsec; /* 2 1 0 */
u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec;
} else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) {
v_nsec = pps_tf[0].tv_nsec; /* 1 0 2 */
u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec;
} else {
v_nsec = pps_tf[2].tv_nsec; /* 1 2 0 */
u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec;
}
}
/*
* Nominal jitter is due to PPS signal noise and interrupt
* latency. If it exceeds the popcorn threshold,
* the sample is discarded. otherwise, if so enabled, the time
* offset is updated. We can tolerate a modest loss of data here
* without degrading time accuracy.
*/
if (u_nsec > (pps_jitter << PPS_POPCORN)) {
time_status |= STA_PPSJITTER;
pps_jitcnt++;
} else if (time_status & STA_PPSTIME) {
L_LINT(ftemp, v_nsec);
L_SUB(ftemp, time_offset);
L_RSHIFT(ftemp, pps_shift);
L_SUB(time_offset, ftemp);
}
pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG;
u_sec = pps_tf[0].tv_sec - pps_lastsec;
if (u_sec < (1 << pps_shift))
return;
/*
* At the end of the calibration interval the difference between
* the first and last counter values becomes the scaled
* frequency. It will later be divided by the length of the
* interval to determine the frequency update. If the frequency
* exceeds a sanity threshold, or if the actual calibration
* interval is not equal to the expected length, the data are
* discarded. We can tolerate a modest loss of data here without
* degrading frequency ccuracy.
*/
pps_calcnt++;
v_nsec = -pps_fcount;
pps_lastsec = pps_tf[0].tv_sec;
pps_fcount = 0;
u_nsec = MAXFREQ << pps_shift;
if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 <<
pps_shift)) {
time_status |= STA_PPSERROR;
pps_errcnt++;
return;
}
/*
* Here the raw frequency offset and wander (stability) is
* calculated. If the wander is less than the wander threshold
* for four consecutive averaging intervals, the interval is
* doubled; if it is greater than the threshold for four
* consecutive intervals, the interval is halved. The scaled
* frequency offset is converted to frequency offset. The
* stability metric is calculated as the average of recent
* frequency changes, but is used only for performance
* monitoring.
*/
L_LINT(ftemp, v_nsec);
L_RSHIFT(ftemp, pps_shift);
L_SUB(ftemp, pps_freq);
u_nsec = L_GINT(ftemp);
if (u_nsec > PPS_MAXWANDER) {
L_LINT(ftemp, PPS_MAXWANDER);
pps_intcnt--;
time_status |= STA_PPSWANDER;
pps_stbcnt++;
} else if (u_nsec < -PPS_MAXWANDER) {
L_LINT(ftemp, -PPS_MAXWANDER);
pps_intcnt--;
time_status |= STA_PPSWANDER;
pps_stbcnt++;
} else {
pps_intcnt++;
}
if (pps_intcnt >= 4) {
pps_intcnt = 4;
if (pps_shift < pps_shiftmax) {
pps_shift++;
pps_intcnt = 0;
}
} else if (pps_intcnt <= -4) {
pps_intcnt = -4;
if (pps_shift > PPS_FAVG) {
pps_shift--;
pps_intcnt = 0;
}
}
if (u_nsec < 0)
u_nsec = -u_nsec;
pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG;
/*
* The PPS frequency is recalculated and clamped to the maximum
* MAXFREQ. If enabled, the system clock frequency is updated as
* well.
*/
L_ADD(pps_freq, ftemp);
u_nsec = L_GINT(pps_freq);
if (u_nsec > MAXFREQ)
L_LINT(pps_freq, MAXFREQ);
else if (u_nsec < -MAXFREQ)
L_LINT(pps_freq, -MAXFREQ);
if (time_status & STA_PPSFREQ)
time_freq = pps_freq;
}
#endif /* PPS_SYNC */
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