LXR linux/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
  65unsigned long random_get_entropy_fallback(void);
  66
  67#include <asm/timex.h>
  68
  69#ifndef random_get_entropy
  70/*
  71 * The random_get_entropy() function is used by the /dev/random driver
  72 * in order to extract entropy via the relative unpredictability of
  73 * when an interrupt takes places versus a high speed, fine-grained
  74 * timing source or cycle counter.  Since it will be occurred on every
  75 * single interrupt, it must have a very low cost/overhead.
  76 *
  77 * By default we use get_cycles() for this purpose, but individual
  78 * architectures may override this in their asm/timex.h header file.
  79 * If a given arch does not have get_cycles(), then we fallback to
  80 * using random_get_entropy_fallback().
  81 */
  82#ifdef get_cycles
  83#define random_get_entropy()    ((unsigned long)get_cycles())
  84#else
  85#define random_get_entropy()    random_get_entropy_fallback()
  86#endif
  87#endif
  88
  89/*
  90 * SHIFT_PLL is used as a dampening factor to define how much we
  91 * adjust the frequency correction for a given offset in PLL mode.
  92 * It also used in dampening the offset correction, to define how
  93 * much of the current value in time_offset we correct for each
  94 * second. Changing this value changes the stiffness of the ntp
  95 * adjustment code. A lower value makes it more flexible, reducing
  96 * NTP convergence time. A higher value makes it stiffer, increasing
  97 * convergence time, but making the clock more stable.
  98 *
  99 * In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
 100 * However this seems to increase convergence time much too long.
 101 *
 102 * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html
 103 *
 104 * In the above mailing list discussion, it seems the value of 4
 105 * was appropriate for other Unix systems with HZ=100, and that
 106 * SHIFT_PLL should be decreased as HZ increases. However, Linux's
 107 * clock steering implementation is HZ independent.
 108 *
 109 * Through experimentation, a SHIFT_PLL value of 2 was found to allow
 110 * for fast convergence (very similar to the NTPv3 code used prior to
 111 * v2.6.19), with good clock stability.
 112 *
 113 *
 114 * SHIFT_FLL is used as a dampening factor to define how much we
 115 * adjust the frequency correction for a given offset in FLL mode.
 116 * In David Mills' nanokernel reference implementation SHIFT_FLL is 2.
 117 *
 118 * MAXTC establishes the maximum time constant of the PLL.
 119 */
 120#define SHIFT_PLL       2       /* PLL frequency factor (shift) */
 121#define SHIFT_FLL       2       /* FLL frequency factor (shift) */
 122#define MAXTC           10      /* maximum time constant (shift) */
 123
 124/*
 125 * SHIFT_USEC defines the scaling (shift) of the time_freq and
 126 * time_tolerance variables, which represent the current frequency
 127 * offset and maximum frequency tolerance.
 128 */
 129#define SHIFT_USEC 16           /* frequency offset scale (shift) */
 130#define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
 131#define PPM_SCALE_INV_SHIFT 19
 132#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
 133                       PPM_SCALE + 1)
 134
 135#define MAXPHASE 500000000L     /* max phase error (ns) */
 136#define MAXFREQ 500000          /* max frequency error (ns/s) */
 137#define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT)
 138#define MINSEC 256              /* min interval between updates (s) */
 139#define MAXSEC 2048             /* max interval between updates (s) */
 140#define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */
 141
 142/*
 143 * kernel variables
 144 * Note: maximum error = NTP sync distance = dispersion + delay / 2;
 145 * estimated error = NTP dispersion.
 146 */
 147extern unsigned long tick_usec;         /* USER_HZ period (usec) */
 148extern unsigned long tick_nsec;         /* SHIFTED_HZ period (nsec) */
 149
 150/* Required to safely shift negative values */
 151#define shift_right(x, s) ({    \
 152        __typeof__(x) __x = (x);        \
 153        __typeof__(s) __s = (s);        \
 154        __x < 0 ? -(-__x >> __s) : __x >> __s;  \
 155})
 156
 157#define NTP_SCALE_SHIFT         32
 158
 159#define NTP_INTERVAL_FREQ  (HZ)
 160#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
 161
 162extern int do_adjtimex(struct __kernel_timex *);
 163extern int do_clock_adjtime(const clockid_t which_clock, struct __kernel_timex * ktx);
 164
 165extern void hardpps(const struct timespec64 *, const struct timespec64 *);
 166
 167int read_current_timer(unsigned long *timer_val);
 168
 169/* The clock frequency of the i8253/i8254 PIT */
 170#define PIT_TICK_RATE 1193182ul
 171
 172#endif /* LINUX_TIMEX_H */
 173