include/linux/timex.h

   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 <uapi/linux/timex.h>
  57
  58 #define ADJ_ADJTIME             0x8000  /* switch between adjtime/adjtimex modes */
  59 #define ADJ_OFFSET_SINGLESHOT   0x0001  /* old-fashioned adjtime */
  60 #define ADJ_OFFSET_READONLY     0x2000  /* read-only adjtime */
  61 #include <linux/compiler.h>
  62 #include <linux/types.h>
  63 #include <linux/param.h>
  64
  65 #include <asm/timex.h>
  66
  67 /*
  68  * SHIFT_PLL is used as a dampening factor to define how much we
  69  * adjust the frequency correction for a given offset in PLL mode.
  70  * It also used in dampening the offset correction, to define how
  71  * much of the current value in time_offset we correct for each
  72  * second. Changing this value changes the stiffness of the ntp
  73  * adjustment code. A lower value makes it more flexible, reducing
  74  * NTP convergence time. A higher value makes it stiffer, increasing
  75  * convergence time, but making the clock more stable.
  76  *
  77  * In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
  78  * However this seems to increase convergence time much too long.
  79  *
  80  * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html
  81  *
  82  * In the above mailing list discussion, it seems the value of 4
  83  * was appropriate for other Unix systems with HZ=100, and that
  84  * SHIFT_PLL should be decreased as HZ increases. However, Linux's
  85  * clock steering implementation is HZ independent.
  86  *
  87  * Through experimentation, a SHIFT_PLL value of 2 was found to allow
  88  * for fast convergence (very similar to the NTPv3 code used prior to
  89  * v2.6.19), with good clock stability.
  90  *
  91  *
  92  * SHIFT_FLL is used as a dampening factor to define how much we
  93  * adjust the frequency correction for a given offset in FLL mode.
  94  * In David Mills' nanokernel reference implementation SHIFT_FLL is 2.
  95  *
  96  * MAXTC establishes the maximum time constant of the PLL.
  97  */
  98 #define SHIFT_PLL       2       /* PLL frequency factor (shift) */
  99 #define SHIFT_FLL       2       /* FLL frequency factor (shift) */
 100 #define MAXTC           10      /* maximum time constant (shift) */
 101
 102 /*
 103  * SHIFT_USEC defines the scaling (shift) of the time_freq and
 104  * time_tolerance variables, which represent the current frequency
 105  * offset and maximum frequency tolerance.
 106  */
 107 #define SHIFT_USEC 16           /* frequency offset scale (shift) */
 108 #define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
 109 #define PPM_SCALE_INV_SHIFT 19
 110 #define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
 111                        PPM_SCALE + 1)
 112
 113 #define MAXPHASE 500000000L     /* max phase error (ns) */
 114 #define MAXFREQ 500000          /* max frequency error (ns/s) */
 115 #define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT)
 116 #define MINSEC 256              /* min interval between updates (s) */
 117 #define MAXSEC 2048             /* max interval between updates (s) */
 118 #define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */
 119
 120 /*
 121  * kernel variables
 122  * Note: maximum error = NTP synch distance = dispersion + delay / 2;
 123  * estimated error = NTP dispersion.
 124  */
 125 extern unsigned long tick_usec;         /* USER_HZ period (usec) */
 126 extern unsigned long tick_nsec;         /* SHIFTED_HZ period (nsec) */
 127
 128 extern void ntp_init(void);
 129 extern void ntp_clear(void);
 130
 131 /* Required to safely shift negative values */
 132 #define shift_right(x, s) ({    \
 133         __typeof__(x) __x = (x);        \
 134         __typeof__(s) __s = (s);        \
 135         __x < 0 ? -(-__x >> __s) : __x >> __s;  \
 136 })
 137
 138 #define NTP_SCALE_SHIFT         32
 139
 140 #define NTP_INTERVAL_FREQ  (HZ)
 141 #define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
 142
 143 /* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
 144 extern u64 ntp_tick_length(void);
 145
 146 extern int second_overflow(unsigned long secs);
 147 extern int do_adjtimex(struct timex *);
 148 extern void hardpps(const struct timespec *, const struct timespec *);
 149
 150 int read_current_timer(unsigned long *timer_val);
 151
 152 /* The clock frequency of the i8253/i8254 PIT */
 153 #define PIT_TICK_RATE 1193182ul
 154
 155 #endif /* LINUX_TIMEX_H */