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linux-next/include/linux/timex.h
Alexander Gordeev 025b40abe7 ntp: add hardpps implementation 
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 <lasaine@lvk.cs.msu.su>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Rodolfo Giometti <giometti@enneenne.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 08:03:20 -08:00

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/*****************************************************************************
* *
* Copyright (c) David L. Mills 1993 *
* *
* 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. *
* *
*****************************************************************************/
/*
* Modification history timex.h
*
* 29 Dec 97 Russell King
* Moved CLOCK_TICK_RATE, CLOCK_TICK_FACTOR and FINETUNE to asm/timex.h
* for ARM machines
*
* 9 Jan 97 Adrian Sun
* Shifted LATCH define to allow access to alpha machines.
*
* 26 Sep 94 David L. Mills
* Added defines for hybrid phase/frequency-lock loop.
*
* 19 Mar 94 David L. Mills
* Moved defines from kernel routines to header file and added new
* defines for PPS phase-lock loop.
*
* 20 Feb 94 David L. Mills
* Revised status codes and structures for external clock and PPS
* signal discipline.
*
* 28 Nov 93 David L. Mills
* Adjusted parameters to improve stability and increase poll
* interval.
*
* 17 Sep 93 David L. Mills
* Created file $NTP/include/sys/timex.h
* 07 Oct 93 Torsten Duwe
* Derived linux/timex.h
* 1995-08-13 Torsten Duwe
* kernel PLL updated to 1994-12-13 specs (rfc-1589)
* 1997-08-30 Ulrich Windl
* Added new constant NTP_PHASE_LIMIT
* 2004-08-12 Christoph Lameter
* Reworked time interpolation logic
*/
#ifndef _LINUX_TIMEX_H
#define _LINUX_TIMEX_H
#include <linux/time.h>
#define NTP_API 4 /* NTP API version */
/*
* syscall interface - used (mainly by NTP daemon)
* to discipline kernel clock oscillator
*/
struct timex {
unsigned int modes; /* mode selector */
long offset; /* time offset (usec) */
long freq; /* frequency offset (scaled ppm) */
long maxerror; /* maximum error (usec) */
long esterror; /* estimated error (usec) */
int status; /* clock command/status */
long constant; /* pll time constant */
long precision; /* clock precision (usec) (read only) */
long tolerance; /* clock frequency tolerance (ppm)
* (read only)
*/
struct timeval time; /* (read only) */
long tick; /* (modified) usecs between clock ticks */
long ppsfreq; /* pps frequency (scaled ppm) (ro) */
long jitter; /* pps jitter (us) (ro) */
int shift; /* interval duration (s) (shift) (ro) */
long stabil; /* pps stability (scaled ppm) (ro) */
long jitcnt; /* jitter limit exceeded (ro) */
long calcnt; /* calibration intervals (ro) */
long errcnt; /* calibration errors (ro) */
long stbcnt; /* stability limit exceeded (ro) */
int tai; /* TAI offset (ro) */
int :32; int :32; int :32; int :32;
int :32; int :32; int :32; int :32;
int :32; int :32; int :32;
};
/*
* Mode codes (timex.mode)
*/
#define ADJ_OFFSET 0x0001 /* time offset */
#define ADJ_FREQUENCY 0x0002 /* frequency offset */
#define ADJ_MAXERROR 0x0004 /* maximum time error */
#define ADJ_ESTERROR 0x0008 /* estimated time error */
#define ADJ_STATUS 0x0010 /* clock status */
#define ADJ_TIMECONST 0x0020 /* pll time constant */
#define ADJ_TAI 0x0080 /* set TAI offset */
#define ADJ_MICRO 0x1000 /* select microsecond resolution */
#define ADJ_NANO 0x2000 /* select nanosecond resolution */
#define ADJ_TICK 0x4000 /* tick value */
#ifdef __KERNEL__
#define ADJ_ADJTIME 0x8000 /* switch between adjtime/adjtimex modes */
#define ADJ_OFFSET_SINGLESHOT 0x0001 /* old-fashioned adjtime */
#define ADJ_OFFSET_READONLY 0x2000 /* read-only adjtime */
#else
#define ADJ_OFFSET_SINGLESHOT 0x8001 /* old-fashioned adjtime */
#define ADJ_OFFSET_SS_READ 0xa001 /* read-only adjtime */
#endif
/* NTP userland likes the MOD_ prefix better */
#define MOD_OFFSET ADJ_OFFSET
#define MOD_FREQUENCY ADJ_FREQUENCY
#define MOD_MAXERROR ADJ_MAXERROR
#define MOD_ESTERROR ADJ_ESTERROR
#define MOD_STATUS ADJ_STATUS
#define MOD_TIMECONST ADJ_TIMECONST
#define MOD_TAI ADJ_TAI
#define MOD_MICRO ADJ_MICRO
#define MOD_NANO ADJ_NANO
/*
* Status codes (timex.status)
*/
#define STA_PLL 0x0001 /* enable PLL updates (rw) */
#define STA_PPSFREQ 0x0002 /* enable PPS freq discipline (rw) */
#define STA_PPSTIME 0x0004 /* enable PPS time discipline (rw) */
#define STA_FLL 0x0008 /* select frequency-lock mode (rw) */
#define STA_INS 0x0010 /* insert leap (rw) */
#define STA_DEL 0x0020 /* delete leap (rw) */
#define STA_UNSYNC 0x0040 /* clock unsynchronized (rw) */
#define STA_FREQHOLD 0x0080 /* hold frequency (rw) */
#define STA_PPSSIGNAL 0x0100 /* PPS signal present (ro) */
#define STA_PPSJITTER 0x0200 /* PPS signal jitter exceeded (ro) */
#define STA_PPSWANDER 0x0400 /* PPS signal wander exceeded (ro) */
#define STA_PPSERROR 0x0800 /* PPS signal calibration error (ro) */
#define STA_CLOCKERR 0x1000 /* clock hardware fault (ro) */
#define STA_NANO 0x2000 /* resolution (0 = us, 1 = ns) (ro) */
#define STA_MODE 0x4000 /* mode (0 = PLL, 1 = FLL) (ro) */
#define STA_CLK 0x8000 /* clock source (0 = A, 1 = B) (ro) */
/* read-only bits */
#define STA_RONLY (STA_PPSSIGNAL | STA_PPSJITTER | STA_PPSWANDER | \
STA_PPSERROR | STA_CLOCKERR | STA_NANO | STA_MODE | STA_CLK)
/*
* Clock states (time_state)
*/
#define TIME_OK 0 /* clock synchronized, no leap second */
#define TIME_INS 1 /* insert leap second */
#define TIME_DEL 2 /* delete leap second */
#define TIME_OOP 3 /* leap second in progress */
#define TIME_WAIT 4 /* leap second has occurred */
#define TIME_ERROR 5 /* clock not synchronized */
#define TIME_BAD TIME_ERROR /* bw compat */
#ifdef __KERNEL__
#include <linux/compiler.h>
#include <linux/types.h>
#include <linux/param.h>
#include <asm/timex.h>
/*
* SHIFT_PLL is used as a dampening factor to define how much we
* adjust the frequency correction for a given offset in PLL mode.
* It also used in dampening the offset correction, to define how
* much of the current value in time_offset we correct for each
* second. Changing this value changes the stiffness of the ntp
* adjustment code. A lower value makes it more flexible, reducing
* NTP convergence time. A higher value makes it stiffer, increasing
* convergence time, but making the clock more stable.
*
* In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
* However this seems to increase convergence time much too long.
*
* https://lists.ntp.org/pipermail/hackers/2008-January/003487.html
*
* In the above mailing list discussion, it seems the value of 4
* was appropriate for other Unix systems with HZ=100, and that
* SHIFT_PLL should be decreased as HZ increases. However, Linux's
* clock steering implementation is HZ independent.
*
* Through experimentation, a SHIFT_PLL value of 2 was found to allow
* for fast convergence (very similar to the NTPv3 code used prior to
* v2.6.19), with good clock stability.
*
*
* SHIFT_FLL is used as a dampening factor to define how much we
* adjust the frequency correction for a given offset in FLL mode.
* In David Mills' nanokernel reference implementation SHIFT_FLL is 2.
*
* MAXTC establishes the maximum time constant of the PLL.
*/
#define SHIFT_PLL 2 /* PLL frequency factor (shift) */
#define SHIFT_FLL 2 /* FLL frequency factor (shift) */
#define MAXTC 10 /* maximum time constant (shift) */
/*
* SHIFT_USEC defines the scaling (shift) of the time_freq and
* time_tolerance variables, which represent the current frequency
* offset and maximum frequency tolerance.
*/
#define SHIFT_USEC 16 /* frequency offset scale (shift) */
#define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
#define PPM_SCALE_INV_SHIFT 19
#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
PPM_SCALE + 1)
#define MAXPHASE 500000000L /* max phase error (ns) */
#define MAXFREQ 500000 /* max frequency error (ns/s) */
#define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT)
#define MINSEC 256 /* min interval between updates (s) */
#define MAXSEC 2048 /* max interval between updates (s) */
#define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */
/*
* kernel variables
* Note: maximum error = NTP synch distance = dispersion + delay / 2;
* estimated error = NTP dispersion.
*/
extern unsigned long tick_usec; /* USER_HZ period (usec) */
extern unsigned long tick_nsec; /* ACTHZ period (nsec) */
/*
* phase-lock loop variables
*/
extern int time_status; /* clock synchronization status bits */
extern void ntp_init(void);
extern void ntp_clear(void);
/**
* ntp_synced - Returns 1 if the NTP status is not UNSYNC
*
*/
static inline int ntp_synced(void)
{
return !(time_status & STA_UNSYNC);
}
/* Required to safely shift negative values */
#define shift_right(x, s) ({ \
__typeof__(x) __x = (x); \
__typeof__(s) __s = (s); \
__x < 0 ? -(-__x >> __s) : __x >> __s; \
})
#define NTP_SCALE_SHIFT 32
#define NTP_INTERVAL_FREQ (HZ)
#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
/* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
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 *);
int read_current_timer(unsigned long *timer_val);
/* The clock frequency of the i8253/i8254 PIT */
#define PIT_TICK_RATE 1193182ul
#endif /* KERNEL */
#endif /* LINUX_TIMEX_H */
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