From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751451Ab0CAIPf (ORCPT ); Mon, 1 Mar 2010 03:15:35 -0500 Received: from 81-174-11-161.static.ngi.it ([81.174.11.161]:45023 "EHLO mail.enneenne.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751107Ab0CAIP3 (ORCPT ); Mon, 1 Mar 2010 03:15:29 -0500 Date: Mon, 1 Mar 2010 09:14:59 +0100 From: Rodolfo Giometti To: Alexander Gordeev Cc: linux-kernel@vger.kernel.org, linuxpps@ml.enneenne.com, "Nikita V. Youshchenko" , stas@lvk.cs.msu.su, john stultz , Andrew Morton , Alan Cox , Ingo Molnar , Bernhard Schiffner , Rik van Riel , Thomas Gleixner , Martin Schwidefsky Message-ID: <20100301081458.GG3671@enneenne.com> Mail-Followup-To: Alexander Gordeev , linux-kernel@vger.kernel.org, linuxpps@ml.enneenne.com, "Nikita V. Youshchenko" , stas@lvk.cs.msu.su, john stultz , Andrew Morton , Alan Cox , Ingo Molnar , Bernhard Schiffner , Rik van Riel , Thomas Gleixner , Martin Schwidefsky References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: GNU/Linux Device Drivers, Embedded Systems and Courses X-PGP-Key: gpg --keyserver keyserver.linux.it --recv-keys D25A5633 User-Agent: Mutt/1.5.20 (2009-06-14) X-SA-Exim-Connect-IP: 192.168.32.37 X-SA-Exim-Mail-From: giometti@enneenne.com Subject: Re: [PATCHv2 1/6] ntp: add hardpps implementation X-SA-Exim-Version: 4.2.1 (built Wed, 25 Jun 2008 17:14:11 +0000) X-SA-Exim-Scanned: Yes (on mail.enneenne.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 24, 2010 at 03:28:12PM +0300, Alexander Gordeev wrote: > This commit adds hardpps() implementation based upon the original one > from the NTPv4 reference kernel code from David Mills. However, it is > highly optimized towards very fast syncronization and maximum stickness > to PPS signal. The typical error is less then a microsecond. > To make it sync faster I had to throw away exponential phase filter so > that the full phase offset is corrected immediately. Then I also had to > throw away median phase filter because it gives a bigger error itself > if used without exponential filter. > Maybe we will find an appropriate filtering scheme in the future but > it's not necessary if the signal quality is ok. > > Signed-off-by: Alexander Gordeev > --- > drivers/pps/Kconfig | 1 + > include/linux/timex.h | 1 + > kernel/time/Kconfig | 7 + > kernel/time/ntp.c | 420 +++++++++++++++++++++++++++++++++++++++++++++++-- > 4 files changed, 414 insertions(+), 15 deletions(-) > > diff --git a/drivers/pps/Kconfig b/drivers/pps/Kconfig > index cc2eb8e..2bd4f65 100644 > --- a/drivers/pps/Kconfig > +++ b/drivers/pps/Kconfig > @@ -7,6 +7,7 @@ menu "PPS support" > config PPS > tristate "PPS support" > depends on EXPERIMENTAL > + select NTP_PPS > ---help--- > PPS (Pulse Per Second) is a special pulse provided by some GPS > antennae. Userland can use it to get a high-precision time > diff --git a/include/linux/timex.h b/include/linux/timex.h > index e6967d1..5a93cd3 100644 > --- a/include/linux/timex.h > +++ b/include/linux/timex.h > @@ -274,6 +274,7 @@ extern u64 tick_length; > extern void second_overflow(void); > extern void update_ntp_one_tick(void); > extern int do_adjtimex(struct timex *); > +extern void hardpps(const struct timespec *, const struct timespec *); > > /* Don't use! Compatibility define for existing users. */ > #define tickadj (500/HZ ? : 1) > diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig > index 95ed429..2da4900 100644 > --- a/kernel/time/Kconfig > +++ b/kernel/time/Kconfig > @@ -27,3 +27,10 @@ config GENERIC_CLOCKEVENTS_BUILD > default y > depends on GENERIC_CLOCKEVENTS || GENERIC_CLOCKEVENTS_MIGR > > +config NTP_PPS > + bool "PPS kernel consumer support" > + depends on PPS > + help > + This option adds support for direct in-kernel time > + syncronization using an external PPS signal. > + This patch is both PPS and NTP related but I suppose is better moving this setting into drivers/pps directory since people whose want to use thise supports can go into same place and find whetever they want... > diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c > index 4800f93..6db097a 100644 > --- a/kernel/time/ntp.c > +++ b/kernel/time/ntp.c > @@ -14,6 +14,7 @@ > #include > #include > #include > +#include > > /* > * NTP timekeeping variables: > @@ -74,6 +75,161 @@ long time_adjust; > /* constant (boot-param configurable) NTP tick adjustment (upscaled) */ > static s64 ntp_tick_adj; > > +#ifdef CONFIG_NTP_PPS > + > +/* > + * The following variables are used when a pulse-per-second (PPS) signal > + * is available. They establish the engineering parameters of the clock > + * discipline loop when controlled by the PPS signal. > + */ > +#define PPS_VALID 120 /* PPS signal watchdog max (s) */ > +#define PPS_POPCORN 4 /* popcorn spike threshold (shift) */ > +#define PPS_INTMIN 2 /* min freq interval (s) (shift) */ > +#define PPS_INTMAX 8 /* max freq interval (s) (shift) */ > +#define PPS_INTCOUNT 4 /* number of consecutive good intervals to > + increase pps_shift or consecutive bad > + intervals to decrease it */ > +#define PPS_MAXWANDER 100000 /* max PPS freq wander (ns/s) */ > + > +static int pps_valid; /* signal watchdog counter */ > +static long pps_tf[3]; /* phase median filter */ > +static long pps_jitter; /* current jitter (ns) */ > +static struct timespec pps_fbase; /* beginning of the last freq interval */ > +static int pps_shift; /* current interval duration (s) (shift) */ > +static int pps_intcnt; /* interval counter */ > +static s64 pps_freq; /* frequency offset (scaled ns/s) */ > +static long pps_stabil; /* current stability (scaled ns/s) */ > + > +/* > + * 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 */ > + > + > +/** > + * pps_clear - Clears the PPS state variables > + * > + * Must be called while holding a write on the xtime_lock > + */ > +static inline void pps_clear(void) > +{ > + pps_shift = PPS_INTMIN; > + pps_tf[0] = 0; > + pps_tf[1] = 0; > + pps_tf[2] = 0; > + pps_fbase.tv_sec = pps_fbase.tv_nsec = 0; > + pps_freq = 0; > +} > + > +/* PPS kernel consumer compensates the whole phase error immediately. > + * Otherwise, reduce the offset by a fixed factor times the time constant. > + */ > +static inline s64 ntp_offset_chunk(s64 offset) > +{ > + if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL) > + return offset; > + else > + return shift_right(offset, SHIFT_PLL + time_constant); > +} > + > +/* Decrease pps_valid to indicate that another second has passed since > + * the last PPS signal. When it reaches 0, indicate that PPS signal is > + * missing. > + * > + * Must be called while holding a write on the xtime_lock > + */ > +static inline void pps_dec_valid(void) > +{ > + if (pps_valid > 0) > + pps_valid--; > + else > + time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER | > + STA_PPSWANDER | STA_PPSERROR); > +} > + > +static inline void pps_reset_freq_interval(void) > +{ > + /* the PPS calibration interval may end > + surprisingly early */ > + pps_shift = PPS_INTMIN; > + pps_intcnt = 0; > +} > + > +static inline void pps_set_freq(s64 freq) > +{ > + pps_freq = freq; > +} > + > +static inline int is_error_status(int status) > +{ > + return (time_status & (STA_UNSYNC|STA_CLOCKERR)) > + /* PPS signal lost when either PPS time or > + * PPS frequency synchronization requested > + */ > + || ((time_status & (STA_PPSFREQ|STA_PPSTIME)) > + && !(time_status & STA_PPSSIGNAL)) > + /* PPS jitter exceeded when > + * PPS time synchronization requested */ > + || ((time_status & (STA_PPSTIME|STA_PPSJITTER)) > + == (STA_PPSTIME|STA_PPSJITTER)) > + /* PPS wander exceeded or calibration error when > + * PPS frequency synchronization requested > + */ > + || ((time_status & STA_PPSFREQ) > + && (time_status & (STA_PPSWANDER|STA_PPSERROR))); > +} > + > +static inline void pps_fill_timex(struct timex *txc) > +{ > + txc->ppsfreq = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) * > + PPM_SCALE_INV, NTP_SCALE_SHIFT); > + txc->jitter = pps_jitter; > + if (!(time_status & STA_NANO)) > + txc->jitter /= NSEC_PER_USEC; > + txc->shift = pps_shift; > + txc->stabil = pps_stabil; > + txc->jitcnt = pps_jitcnt; > + txc->calcnt = pps_calcnt; > + txc->errcnt = pps_errcnt; > + txc->stbcnt = pps_stbcnt; > +} > + > +#else /* !CONFIG_NTP_PPS */ > + > +static inline void pps_clear(void) {} > + > +static inline s64 ntp_offset_chunk(s64 offset) > +{ > + return shift_right(offset, SHIFT_PLL + time_constant); > +} > + > +static inline void pps_dec_valid(void) {} > +static inline void pps_reset_freq_interval(void) {} > +static inline void pps_set_freq(s64 freq) {} > + > +static inline int is_error_status(int status) > +{ > + return status & (STA_UNSYNC|STA_CLOCKERR); > +} > + > +static inline void pps_fill_timex(struct timex *txc) > +{ > + /* PPS is not implemented, so these are zero */ > + txc->ppsfreq = 0; > + txc->jitter = 0; > + txc->shift = 0; > + txc->stabil = 0; > + txc->jitcnt = 0; > + txc->calcnt = 0; > + txc->errcnt = 0; > + txc->stbcnt = 0; > +} > + > +#endif /* CONFIG_NTP_PPS */ > + > /* > * NTP methods: > */ > @@ -177,6 +333,9 @@ void ntp_clear(void) > > tick_length = tick_length_base; > time_offset = 0; > + > + /* Clear PPS state variables */ > + pps_clear(); > } > > /* > @@ -242,16 +401,16 @@ void second_overflow(void) > time_status |= STA_UNSYNC; > } > > - /* > - * Compute the phase adjustment for the next second. The offset is > - * reduced by a fixed factor times the time constant. > - */ > + /* Compute the phase adjustment for the next second */ > tick_length = tick_length_base; > > - delta = shift_right(time_offset, SHIFT_PLL + time_constant); > + delta = ntp_offset_chunk(time_offset); > time_offset -= delta; > tick_length += delta; > > + /* Check PPS signal */ > + pps_dec_valid(); > + > if (!time_adjust) > return; > > @@ -361,6 +520,8 @@ static inline void process_adj_status(struct timex *txc, struct timespec *ts) > if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) { > time_state = TIME_OK; > time_status = STA_UNSYNC; > + /* restart PPS frequency calibration */ > + pps_reset_freq_interval(); > } > > /* > @@ -410,6 +571,8 @@ static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts > time_freq = txc->freq * PPM_SCALE; > time_freq = min(time_freq, MAXFREQ_SCALED); > time_freq = max(time_freq, -MAXFREQ_SCALED); > + /* update pps_freq */ > + pps_set_freq(time_freq); > } > > if (txc->modes & ADJ_MAXERROR) > @@ -500,7 +663,8 @@ int do_adjtimex(struct timex *txc) > } > > result = time_state; /* mostly `TIME_OK' */ > - if (time_status & (STA_UNSYNC|STA_CLOCKERR)) > + /* check for errors */ > + if (is_error_status(time_status)) > result = TIME_ERROR; > > txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) * > @@ -514,15 +678,8 @@ int do_adjtimex(struct timex *txc) > txc->tick = tick_usec; > txc->tai = time_tai; > > - /* PPS is not implemented, so these are zero */ > - txc->ppsfreq = 0; > - txc->jitter = 0; > - txc->shift = 0; > - txc->stabil = 0; > - txc->jitcnt = 0; > - txc->calcnt = 0; > - txc->errcnt = 0; > - txc->stbcnt = 0; > + /* fill PPS status fields */ > + pps_fill_timex(txc); > > write_sequnlock_irq(&xtime_lock); > > @@ -536,6 +693,239 @@ int do_adjtimex(struct timex *txc) > return result; > } > > +#ifdef CONFIG_NTP_PPS > + > +struct pps_normtime { > + __kernel_time_t sec; /* seconds */ > + long nsec; /* nanoseconds */ > +}; > + > +/* normalize the timestamp so that nsec is in the > + ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */ > +static inline struct pps_normtime pps_normalize_ts(struct timespec ts) > +{ > + struct pps_normtime norm = { > + .sec = ts.tv_sec, > + .nsec = ts.tv_nsec > + }; > + > + if (norm.nsec > (NSEC_PER_SEC >> 1)) { > + norm.nsec -= NSEC_PER_SEC; > + norm.sec++; > + } > + > + return norm; > +} > + > +/* get current phase correction and jitter */ > +static inline long pps_phase_filter_get(long *jitter) > +{ > + *jitter = pps_tf[0] - pps_tf[1]; > + if (*jitter < 0) > + *jitter = -*jitter; > + > + /* TODO: test various filters */ > + return pps_tf[0]; > +} > + > +/* add the sample to the phase filter */ > +static inline void pps_phase_filter_add(long err) > +{ > + pps_tf[2] = pps_tf[1]; > + pps_tf[1] = pps_tf[0]; > + pps_tf[0] = err; > +} > + > +/* decrease frequency calibration interval length. > + * It is halved after four consecutive unstable intervals. > + */ > +static inline void pps_dec_freq_interval(void) > +{ > + if (--pps_intcnt <= -PPS_INTCOUNT) { > + pps_intcnt = -PPS_INTCOUNT; > + if (pps_shift > PPS_INTMIN) { > + pps_shift--; > + pps_intcnt = 0; > + } > + } > +} > + > +/* increase frequency calibration interval length. > + * It is doubled after four consecutive stable intervals. > + */ > +static inline void pps_inc_freq_interval(void) > +{ > + if (++pps_intcnt >= PPS_INTCOUNT) { > + pps_intcnt = PPS_INTCOUNT; > + if (pps_shift < PPS_INTMAX) { > + pps_shift++; > + pps_intcnt = 0; > + } > + } > +} > + > +/* update clock frequency based on MONOTONIC_RAW clock PPS signal > + * timestamps > + * > + * At the end of the calibration interval the difference between the > + * first and last MONOTONIC_RAW clock timestamps divided by the length > + * of the interval becomes the frequency update. If the interval was > + * too long, the data are discarded. > + * Returns the difference between old and new frequency values. > + */ > +static long hardpps_update_freq(struct pps_normtime freq_norm) > +{ > + long delta, delta_mod; > + s64 ftemp; > + > + /* check if the frequency interval was too long */ > + if (freq_norm.sec > (2 << pps_shift)) { > + time_status |= STA_PPSERROR; > + pps_errcnt++; > + pps_dec_freq_interval(); > + pr_err("hardpps: PPSERROR: interval too long - %ld s\n", > + freq_norm.sec); > + return 0; > + } > + > + /* here the raw frequency offset and wander (stability) is > + * calculated. If the wander is less than the wander threshold > + * the interval is increased; otherwise it is decreased. > + */ > + ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT, > + freq_norm.sec); > + delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT); > + pps_freq = ftemp; > + if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) { > + pr_warning("hardpps: PPSWANDER: change=%ld\n", delta); > + time_status |= STA_PPSWANDER; > + pps_stbcnt++; > + pps_dec_freq_interval(); > + } else { /* good sample */ > + pps_inc_freq_interval(); > + } > + > + /* the stability metric is calculated as the average of recent > + * frequency changes, but is used only for performance > + * monitoring > + */ > + delta_mod = delta; > + if (delta_mod < 0) > + delta_mod = -delta_mod; > + pps_stabil += (div_s64(((s64)delta_mod) << > + (NTP_SCALE_SHIFT - SHIFT_USEC), > + NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN; > + > + /* if enabled, the system clock frequency is updated */ > + if ((time_status & STA_PPSFREQ) != 0 && > + (time_status & STA_FREQHOLD) == 0) { > + time_freq = pps_freq; > + ntp_update_frequency(); > + } > + > + return delta; > +} > + > +/* correct REALTIME clock phase error against PPS signal */ > +static void hardpps_update_phase(long error) > +{ > + long correction = -error; > + long jitter; > + > + /* add the sample to the median filter */ > + pps_phase_filter_add(correction); > + correction = pps_phase_filter_get(&jitter); > + > + /* Nominal jitter is due to PPS signal noise. If it exceeds the > + * threshold, the sample is discarded; otherwise, if so enabled, > + * the time offset is updated. > + */ > + if (jitter > (pps_jitter << PPS_POPCORN)) { > + pr_warning("hardpps: PPSJITTER: jitter=%ld, limit=%ld\n", > + jitter, (pps_jitter << PPS_POPCORN)); > + time_status |= STA_PPSJITTER; > + pps_jitcnt++; > + } else if (time_status & STA_PPSTIME) { > + /* correct the time using the phase offset */ > + time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT, > + NTP_INTERVAL_FREQ); > + /* cancel running adjtime() */ > + time_adjust = 0; > + } > + /* update jitter */ > + pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN; > +} > + > +/* > + * hardpps() - discipline CPU clock oscillator to external PPS signal > + * > + * This routine is called at each PPS signal arrival in order to > + * discipline the CPU clock oscillator to the PPS signal. It takes two > + * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former > + * is used to correct clock phase error and the latter is used to > + * correct the frequency. > + * > + * This code is based on David Mills's reference nanokernel > + * implementation. It was mostly rewritten but keeps the same idea. > + */ > +void hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts) > +{ > + struct pps_normtime pts_norm, freq_norm; > + unsigned long flags; > + > + pts_norm = pps_normalize_ts(*phase_ts); > + > + write_seqlock_irqsave(&xtime_lock, flags); > + > + /* clear the error bits, they will be set again if needed */ > + time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR); > + > + /* indicate signal presence */ > + time_status |= STA_PPSSIGNAL; > + pps_valid = PPS_VALID; > + > + /* when called for the first time, > + * just start the frequency interval */ > + if (unlikely(pps_fbase.tv_sec == 0)) { > + pps_fbase = *raw_ts; > + write_sequnlock_irq(&xtime_lock); > + return; > + } > + > + /* ok, now we have a base for frequency calculation */ > + freq_norm = pps_normalize_ts(timespec_sub(*raw_ts, pps_fbase)); > + > + /* check that the signal is in the range > + * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */ > + if ((freq_norm.sec == 0) || > + (freq_norm.nsec > MAXFREQ * freq_norm.sec) || > + (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) { > + time_status |= STA_PPSJITTER; > + /* restart the frequency calibration interval */ > + pps_fbase = *raw_ts; > + write_sequnlock_irqrestore(&xtime_lock, flags); > + pr_err("hardpps: PPSJITTER: bad pulse\n"); > + return; > + } > + > + /* signal is ok */ > + > + /* check if the current frequency interval is finished */ > + if (freq_norm.sec >= (1 << pps_shift)) { > + pps_calcnt++; > + /* restart the frequency calibration interval */ > + pps_fbase = *raw_ts; > + hardpps_update_freq(freq_norm); > + } > + > + hardpps_update_phase(pts_norm.nsec); > + > + write_sequnlock_irqrestore(&xtime_lock, flags); > +} > +EXPORT_SYMBOL(hardpps); > + > +#endif /* CONFIG_NTP_PPS */ > + > static int __init ntp_tick_adj_setup(char *str) > { > ntp_tick_adj = simple_strtol(str, NULL, 0); > -- > 1.6.6.1 > -- GNU/Linux Solutions e-mail: giometti@enneenne.com Linux Device Driver giometti@linux.it Embedded Systems phone: +39 349 2432127 UNIX programming skype: rodolfo.giometti Freelance ICT Italia - Consulente ICT Italia - www.consulenti-ict.it