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/* Required to safely shift negative values */
143#define shift_right(x, s) ({	\
144	__typeof__(x) __x = (x);	\
145	__typeof__(s) __s = (s);	\
146	__x < 0 ? -(-__x >> __s) : __x >> __s;	\
147})
148
149#define NTP_SCALE_SHIFT		32
150
151#define NTP_INTERVAL_FREQ  (HZ)
152#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
153
154extern int do_adjtimex(struct __kernel_timex *);
155extern int do_clock_adjtime(const clockid_t which_clock, struct __kernel_timex * ktx);
156
157extern void hardpps(const struct timespec64 *, const struct timespec64 *);
158
159int read_current_timer(unsigned long *timer_val);
160
161/* The clock frequency of the i8253/i8254 PIT */
162#define PIT_TICK_RATE 1193182ul
163
164#endif /* LINUX_TIMEX_H */