/*********************************************************************** * * * Copyright (c) David L. Mills 1993-2001 * * * * 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 . * * 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. * * $FreeBSD: src/sys/kern/kern_ntptime.c,v 1.32.2.2 2001/04/22 11:19:46 jhay Exp $ */ #include "opt_ntp.h" #include #include #include #include #include #include #include #include #include #include #include /* * 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_tai; /* TAI offset (s) */ static long time_monitor; /* last time offset scaled (ns) */ 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 time_t 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) */ static l_fp time_adj; /* tick adjust (ns/s) */ static struct lock ntp_lock = LOCK_INITIALIZER("ntplk", 0, 0); #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 8 /* 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. Note * that the TAI offset is returned in the ntvtimeval.tai structure * member. */ static int ntp_sysctl(SYSCTL_HANDLER_ARGS) { struct ntptimeval ntv; /* temporary structure */ struct timespec atv; /* nanosecond time */ int error; lockmgr(&ntp_lock, LK_EXCLUSIVE); 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.tai = time_tai; 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; } error = sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req); lockmgr(&ntp_lock, LK_RELEASE); return error; } 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, ""); SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shift, CTLFLAG_RW, &pps_shift, 0, ""); SYSCTL_INT(_kern_ntp_pll, OID_AUTO, time_monitor, CTLFLAG_RD, &time_monitor, 0, ""); SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, &pps_freq, sizeof(pps_freq), "I", ""); SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, time_freq, CTLFLAG_RD, &time_freq, sizeof(time_freq), "I", ""); #endif /* * ntp_adjtime() - NTP daemon application interface * * See the timex.h header file for synopsis and API description. Note * that the timex.constant structure member has a dual purpose to set * the time constant and to set the TAI offset. * * MPALMOSTSAFE */ int sys_ntp_adjtime(struct sysmsg *sysmsg, const struct ntp_adjtime_args *uap) { struct timex ntv; /* temporary structure */ long freq; /* frequency ns/s) */ int modes; /* mode bits from structure */ 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. * Note that either the time constant or TAI offset are loaded * from the ntv.constant member, depending on the mode bits. If * the STA_PLL bit in the status word is cleared, the state and * status words are reset to the initial values at boot. */ modes = ntv.modes; if (modes) error = caps_priv_check_self(SYSCAP_NOSETTIME); if (error) return (error); lockmgr(&ntp_lock, LK_EXCLUSIVE); crit_enter(); if (modes & MOD_MAXERROR) time_maxerror = ntv.maxerror; if (modes & MOD_ESTERROR) time_esterror = ntv.esterror; if (modes & MOD_STATUS) { if (time_status & STA_PLL && !(ntv.status & STA_PLL)) { time_state = TIME_OK; time_status = STA_UNSYNC; #ifdef PPS_SYNC pps_shift = PPS_FAVG; #endif /* PPS_SYNC */ } 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; } if (modes & MOD_TAI) { if (ntv.constant > 0) /* XXX zero & negative numbers ? */ time_tai = 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); } /* * Note: the userland specified frequency is in seconds per second * times 65536e+6. Multiply by a thousand and divide by 65336 to * get nanoseconds. */ 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 */ } /* * Retrieve all clock variables. Note that the TAI offset is * returned only by ntp_gettime(); */ if (time_status & STA_NANO) ntv.offset = time_monitor; else ntv.offset = time_monitor / 1000; /* XXX rounding ? */ 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 */ crit_exit(); lockmgr(&ntp_lock, LK_RELEASE); 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))) { sysmsg->sysmsg_result = TIME_ERROR; } else { sysmsg->sysmsg_result = time_state; } return (0); } /* * second_overflow() - called after ntp_tick_adjust() * * This routine is ordinarily called from hardclock() whenever the seconds * hand rolls over. It returns leap seconds to add or drop, and sets nsec_adj * to the total adjustment to make over the next second in (ns << 32). * * This routine is only called by cpu #0. */ int ntp_update_second(time_t newsec, int64_t *nsec_adj) { l_fp ftemp; /* 32/64-bit temporary */ int adjsec = 0; /* * 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) { --adjsec; 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) { ++adjsec; time_tai--; time_state = TIME_WAIT; } break; /* * Insert second in progress. */ case TIME_OOP: time_tai++; 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; } /* * time_offset represents the total time adjustment we wish to * make (over no particular period of time). time_freq represents * the frequency compensation we wish to apply. * * time_adj represents the total adjustment we wish to make over * one full second. hardclock usually applies this adjustment in * time_adj / hz jumps, hz times a second. */ ftemp = time_offset; #ifdef PPS_SYNC /* XXX even if PPS signal dies we should finish adjustment ? */ if ((time_status & STA_PPSTIME) && (time_status & STA_PPSSIGNAL)) L_RSHIFT(ftemp, pps_shift); else L_RSHIFT(ftemp, SHIFT_PLL + time_constant); #else L_RSHIFT(ftemp, SHIFT_PLL + time_constant); #endif /* PPS_SYNC */ time_adj = ftemp; /* adjustment for part of the offset */ L_SUB(time_offset, ftemp); L_ADD(time_adj, time_freq); /* add frequency correction */ *nsec_adj = time_adj; #ifdef PPS_SYNC if (pps_valid > 0) pps_valid--; else time_status &= ~STA_PPSSIGNAL; #endif /* PPS_SYNC */ return(adjsec); } /* * 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(void) { /* * 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_BOOT2_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(long offset) { long 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; if (!((time_status & STA_PPSTIME) && (time_status & STA_PPSSIGNAL))) { if (offset > MAXPHASE) time_monitor = MAXPHASE; else if (offset < -MAXPHASE) time_monitor = -MAXPHASE; else time_monitor = offset; L_LINT(time_offset, time_monitor); } /* * 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_uptime; return; } if ((time_status & STA_FREQHOLD) || time_reftime == 0) time_reftime = time_uptime; mtemp = time_uptime - time_reftime; L_LINT(ftemp, time_monitor); 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, (time_monitor << 4) / mtemp); L_RSHIFT(ftemp, SHIFT_FLL + 4); L_ADD(time_freq, ftemp); time_status |= STA_MODE; } time_reftime = time_uptime; 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. There are two independent * first-order feedback loops, one for the phase, the other for the * frequency. The phase loop measures and grooms the PPS phase offset * and leaves it in a handy spot for the seconds overflow routine. The * frequency loop averages successive PPS phase differences and * calculates the PPS frequency offset, which is also processed by the * seconds overflow routine. 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(struct timespec *tsp, long nsec) { long u_sec, u_nsec, v_nsec; /* temps */ l_fp ftemp; /* * The signal is first processed by a range gate and frequency * discriminator. The range gate rejects noise spikes outside * the range +-500 us. The frequency discriminator rejects input * signals with apparent frequency outside the range 1 +-500 * PPM. 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 for later comparison, 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 < NANOSECOND - 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 * much degrading time accuracy. */ if (u_nsec > (pps_jitter << PPS_POPCORN)) { time_status |= STA_PPSJITTER; pps_jitcnt++; } else if (time_status & STA_PPSTIME) { time_monitor = -v_nsec; L_LINT(time_offset, time_monitor); } 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 * much degrading frequency accuracy. */ 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_shift > pps_shiftmax) { 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 */