linux/include/linux/timex.h
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   1/*****************************************************************************
   2 *                                                                           *
   3 * Copyright (c) David L. Mills 1993                                         *
   4 *                                                                           *
   5 * Permission to use, copy, modify, and distribute this software and its     *
   6 * documentation for any purpose and without fee is hereby granted, provided *
   7 * that the above copyright notice appears in all copies and that both the   *
   8 * copyright notice and this permission notice appear in supporting          *
   9 * documentation, and that the name University of Delaware not be used in    *
  10 * advertising or publicity pertaining to distribution of the software       *
  11 * without specific, written prior permission.  The University of Delaware   *
  12 * makes no representations about the suitability this software for any      *
  13 * purpose.  It is provided "as is" without express or implied warranty.     *
  14 *                                                                           *
  15 *****************************************************************************/
  16
  17/*
  18 * Modification history timex.h
  19 *
  20 * 29 Dec 97    Russell King
  21 *      Moved CLOCK_TICK_RATE, CLOCK_TICK_FACTOR and FINETUNE to asm/timex.h
  22 *      for ARM machines
  23 *
  24 *  9 Jan 97    Adrian Sun
  25 *      Shifted LATCH define to allow access to alpha machines.
  26 *
  27 * 26 Sep 94    David L. Mills
  28 *      Added defines for hybrid phase/frequency-lock loop.
  29 *
  30 * 19 Mar 94    David L. Mills
  31 *      Moved defines from kernel routines to header file and added new
  32 *      defines for PPS phase-lock loop.
  33 *
  34 * 20 Feb 94    David L. Mills
  35 *      Revised status codes and structures for external clock and PPS
  36 *      signal discipline.
  37 *
  38 * 28 Nov 93    David L. Mills
  39 *      Adjusted parameters to improve stability and increase poll
  40 *      interval.
  41 *
  42 * 17 Sep 93    David L. Mills
  43 *      Created file $NTP/include/sys/timex.h
  44 * 07 Oct 93    Torsten Duwe
  45 *      Derived linux/timex.h
  46 * 1995-08-13    Torsten Duwe
  47 *      kernel PLL updated to 1994-12-13 specs (rfc-1589)
  48 * 1997-08-30    Ulrich Windl
  49 *      Added new constant NTP_PHASE_LIMIT
  50 * 2004-08-12    Christoph Lameter
  51 *      Reworked time interpolation logic
  52 */
  53#ifndef _LINUX_TIMEX_H
  54#define _LINUX_TIMEX_H
  55
  56#include <linux/time.h>
  57
  58#define NTP_API         4       /* NTP API version */
  59
  60/*
  61 * syscall interface - used (mainly by NTP daemon)
  62 * to discipline kernel clock oscillator
  63 */
  64struct timex {
  65        unsigned int modes;     /* mode selector */
  66        long offset;            /* time offset (usec) */
  67        long freq;              /* frequency offset (scaled ppm) */
  68        long maxerror;          /* maximum error (usec) */
  69        long esterror;          /* estimated error (usec) */
  70        int status;             /* clock command/status */
  71        long constant;          /* pll time constant */
  72        long precision;         /* clock precision (usec) (read only) */
  73        long tolerance;         /* clock frequency tolerance (ppm)
  74                                 * (read only)
  75                                 */
  76        struct timeval time;    /* (read only, except for ADJ_SETOFFSET) */
  77        long tick;              /* (modified) usecs between clock ticks */
  78
  79        long ppsfreq;           /* pps frequency (scaled ppm) (ro) */
  80        long jitter;            /* pps jitter (us) (ro) */
  81        int shift;              /* interval duration (s) (shift) (ro) */
  82        long stabil;            /* pps stability (scaled ppm) (ro) */
  83        long jitcnt;            /* jitter limit exceeded (ro) */
  84        long calcnt;            /* calibration intervals (ro) */
  85        long errcnt;            /* calibration errors (ro) */
  86        long stbcnt;            /* stability limit exceeded (ro) */
  87
  88        int tai;                /* TAI offset (ro) */
  89
  90        int  :32; int  :32; int  :32; int  :32;
  91        int  :32; int  :32; int  :32; int  :32;
  92        int  :32; int  :32; int  :32;
  93};
  94
  95/*
  96 * Mode codes (timex.mode)
  97 */
  98#define ADJ_OFFSET              0x0001  /* time offset */
  99#define ADJ_FREQUENCY           0x0002  /* frequency offset */
 100#define ADJ_MAXERROR            0x0004  /* maximum time error */
 101#define ADJ_ESTERROR            0x0008  /* estimated time error */
 102#define ADJ_STATUS              0x0010  /* clock status */
 103#define ADJ_TIMECONST           0x0020  /* pll time constant */
 104#define ADJ_TAI                 0x0080  /* set TAI offset */
 105#define ADJ_SETOFFSET           0x0100  /* add 'time' to current time */
 106#define ADJ_MICRO               0x1000  /* select microsecond resolution */
 107#define ADJ_NANO                0x2000  /* select nanosecond resolution */
 108#define ADJ_TICK                0x4000  /* tick value */
 109
 110#ifdef __KERNEL__
 111#define ADJ_ADJTIME             0x8000  /* switch between adjtime/adjtimex modes */
 112#define ADJ_OFFSET_SINGLESHOT   0x0001  /* old-fashioned adjtime */
 113#define ADJ_OFFSET_READONLY     0x2000  /* read-only adjtime */
 114#else
 115#define ADJ_OFFSET_SINGLESHOT   0x8001  /* old-fashioned adjtime */
 116#define ADJ_OFFSET_SS_READ      0xa001  /* read-only adjtime */
 117#endif
 118
 119/* NTP userland likes the MOD_ prefix better */
 120#define MOD_OFFSET      ADJ_OFFSET
 121#define MOD_FREQUENCY   ADJ_FREQUENCY
 122#define MOD_MAXERROR    ADJ_MAXERROR
 123#define MOD_ESTERROR    ADJ_ESTERROR
 124#define MOD_STATUS      ADJ_STATUS
 125#define MOD_TIMECONST   ADJ_TIMECONST
 126#define MOD_TAI ADJ_TAI
 127#define MOD_MICRO       ADJ_MICRO
 128#define MOD_NANO        ADJ_NANO
 129
 130
 131/*
 132 * Status codes (timex.status)
 133 */
 134#define STA_PLL         0x0001  /* enable PLL updates (rw) */
 135#define STA_PPSFREQ     0x0002  /* enable PPS freq discipline (rw) */
 136#define STA_PPSTIME     0x0004  /* enable PPS time discipline (rw) */
 137#define STA_FLL         0x0008  /* select frequency-lock mode (rw) */
 138
 139#define STA_INS         0x0010  /* insert leap (rw) */
 140#define STA_DEL         0x0020  /* delete leap (rw) */
 141#define STA_UNSYNC      0x0040  /* clock unsynchronized (rw) */
 142#define STA_FREQHOLD    0x0080  /* hold frequency (rw) */
 143
 144#define STA_PPSSIGNAL   0x0100  /* PPS signal present (ro) */
 145#define STA_PPSJITTER   0x0200  /* PPS signal jitter exceeded (ro) */
 146#define STA_PPSWANDER   0x0400  /* PPS signal wander exceeded (ro) */
 147#define STA_PPSERROR    0x0800  /* PPS signal calibration error (ro) */
 148
 149#define STA_CLOCKERR    0x1000  /* clock hardware fault (ro) */
 150#define STA_NANO        0x2000  /* resolution (0 = us, 1 = ns) (ro) */
 151#define STA_MODE        0x4000  /* mode (0 = PLL, 1 = FLL) (ro) */
 152#define STA_CLK         0x8000  /* clock source (0 = A, 1 = B) (ro) */
 153
 154/* read-only bits */
 155#define STA_RONLY (STA_PPSSIGNAL | STA_PPSJITTER | STA_PPSWANDER | \
 156        STA_PPSERROR | STA_CLOCKERR | STA_NANO | STA_MODE | STA_CLK)
 157
 158/*
 159 * Clock states (time_state)
 160 */
 161#define TIME_OK         0       /* clock synchronized, no leap second */
 162#define TIME_INS        1       /* insert leap second */
 163#define TIME_DEL        2       /* delete leap second */
 164#define TIME_OOP        3       /* leap second in progress */
 165#define TIME_WAIT       4       /* leap second has occurred */
 166#define TIME_ERROR      5       /* clock not synchronized */
 167#define TIME_BAD        TIME_ERROR /* bw compat */
 168
 169#ifdef __KERNEL__
 170#include <linux/compiler.h>
 171#include <linux/types.h>
 172#include <linux/param.h>
 173
 174#include <asm/timex.h>
 175
 176/*
 177 * SHIFT_PLL is used as a dampening factor to define how much we
 178 * adjust the frequency correction for a given offset in PLL mode.
 179 * It also used in dampening the offset correction, to define how
 180 * much of the current value in time_offset we correct for each
 181 * second. Changing this value changes the stiffness of the ntp
 182 * adjustment code. A lower value makes it more flexible, reducing
 183 * NTP convergence time. A higher value makes it stiffer, increasing
 184 * convergence time, but making the clock more stable.
 185 *
 186 * In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
 187 * However this seems to increase convergence time much too long.
 188 *
 189 * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html
 190 *
 191 * In the above mailing list discussion, it seems the value of 4
 192 * was appropriate for other Unix systems with HZ=100, and that
 193 * SHIFT_PLL should be decreased as HZ increases. However, Linux's
 194 * clock steering implementation is HZ independent.
 195 *
 196 * Through experimentation, a SHIFT_PLL value of 2 was found to allow
 197 * for fast convergence (very similar to the NTPv3 code used prior to
 198 * v2.6.19), with good clock stability.
 199 *
 200 *
 201 * SHIFT_FLL is used as a dampening factor to define how much we
 202 * adjust the frequency correction for a given offset in FLL mode.
 203 * In David Mills' nanokernel reference implementation SHIFT_FLL is 2.
 204 *
 205 * MAXTC establishes the maximum time constant of the PLL.
 206 */
 207#define SHIFT_PLL       2       /* PLL frequency factor (shift) */
 208#define SHIFT_FLL       2       /* FLL frequency factor (shift) */
 209#define MAXTC           10      /* maximum time constant (shift) */
 210
 211/*
 212 * SHIFT_USEC defines the scaling (shift) of the time_freq and
 213 * time_tolerance variables, which represent the current frequency
 214 * offset and maximum frequency tolerance.
 215 */
 216#define SHIFT_USEC 16           /* frequency offset scale (shift) */
 217#define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
 218#define PPM_SCALE_INV_SHIFT 19
 219#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
 220                       PPM_SCALE + 1)
 221
 222#define MAXPHASE 500000000L     /* max phase error (ns) */
 223#define MAXFREQ 500000          /* max frequency error (ns/s) */
 224#define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT)
 225#define MINSEC 256              /* min interval between updates (s) */
 226#define MAXSEC 2048             /* max interval between updates (s) */
 227#define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */
 228
 229/*
 230 * kernel variables
 231 * Note: maximum error = NTP synch distance = dispersion + delay / 2;
 232 * estimated error = NTP dispersion.
 233 */
 234extern unsigned long tick_usec;         /* USER_HZ period (usec) */
 235extern unsigned long tick_nsec;         /* SHIFTED_HZ period (nsec) */
 236
 237extern void ntp_init(void);
 238extern void ntp_clear(void);
 239
 240/* Required to safely shift negative values */
 241#define shift_right(x, s) ({    \
 242        __typeof__(x) __x = (x);        \
 243        __typeof__(s) __s = (s);        \
 244        __x < 0 ? -(-__x >> __s) : __x >> __s;  \
 245})
 246
 247#define NTP_SCALE_SHIFT         32
 248
 249#define NTP_INTERVAL_FREQ  (HZ)
 250#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
 251
 252/* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
 253extern u64 ntp_tick_length(void);
 254
 255extern int second_overflow(unsigned long secs);
 256extern int do_adjtimex(struct timex *);
 257extern void hardpps(const struct timespec *, const struct timespec *);
 258
 259int read_current_timer(unsigned long *timer_val);
 260
 261/* The clock frequency of the i8253/i8254 PIT */
 262#define PIT_TICK_RATE 1193182ul
 263
 264#endif /* KERNEL */
 265
 266#endif /* LINUX_TIMEX_H */
 267
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