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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*****************************************************************************
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
David Howells607ca462012-10-13 10:46:48 +010056#include <uapi/linux/timex.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070057
Roman Zippel916c7a82008-08-20 16:46:08 -070058#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 */
Mike Frysingerc29541b2008-12-01 14:18:11 -080061#include <linux/compiler.h>
62#include <linux/types.h>
63#include <linux/param.h>
64
David Woodhouseee6baf82006-09-12 20:36:03 -070065#include <asm/timex.h>
66
Linus Torvalds1da177e2005-04-16 15:20:36 -070067/*
john stultz22cfbbf2009-05-06 11:43:57 +020068 * 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.
Mike Frysingerc29541b2008-12-01 14:18:11 -080076 *
john stultze13cf6e2009-05-11 18:13:13 -070077 * In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
john stultz22cfbbf2009-05-06 11:43:57 +020078 * 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.
john stultze13cf6e2009-05-11 18:13:13 -070094 * In David Mills' nanokernel reference implementation SHIFT_FLL is 2.
john stultz22cfbbf2009-05-06 11:43:57 +020095 *
96 * MAXTC establishes the maximum time constant of the PLL.
Mike Frysingerc29541b2008-12-01 14:18:11 -080097 */
john stultz22cfbbf2009-05-06 11:43:57 +020098#define SHIFT_PLL 2 /* PLL frequency factor (shift) */
Mike Frysingerc29541b2008-12-01 14:18:11 -080099#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) */
Ingo Molnar2b9d1492009-02-22 15:48:43 +0100108#define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
Mike Frysingerc29541b2008-12-01 14:18:11 -0800109#define PPM_SCALE_INV_SHIFT 19
john stultz22cfbbf2009-05-06 11:43:57 +0200110#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
Mike Frysingerc29541b2008-12-01 14:18:11 -0800111 PPM_SCALE + 1)
112
john stultz22cfbbf2009-05-06 11:43:57 +0200113#define MAXPHASE 500000000L /* max phase error (ns) */
Mike Frysingerc29541b2008-12-01 14:18:11 -0800114#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/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700121 * kernel variables
122 * Note: maximum error = NTP synch distance = dispersion + delay / 2;
123 * estimated error = NTP dispersion.
124 */
125extern unsigned long tick_usec; /* USER_HZ period (usec) */
John Stultz02ab20a2012-07-27 14:48:10 -0400126extern unsigned long tick_nsec; /* SHIFTED_HZ period (nsec) */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700127
Roman Zippel7dffa3c2008-05-01 04:34:41 -0700128extern void ntp_init(void);
Roman Zippelb0ee7552006-09-30 23:28:22 -0700129extern void ntp_clear(void);
john stultzb149ee22005-09-06 15:17:46 -0700130
john stultz1bb34a42005-10-30 15:01:42 -0800131/* 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
Roman Zippel7fc5c782008-05-01 04:34:38 -0700138#define NTP_SCALE_SHIFT 32
Roman Zippel19923c12006-06-26 00:25:18 -0700139
john stultzf4304ab2007-02-16 01:27:26 -0800140#define NTP_INTERVAL_FREQ (HZ)
Roman Zippel10a398d2008-03-04 15:14:26 -0800141#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
john stultzf4304ab2007-02-16 01:27:26 -0800142
Roman Zippel8383c422008-05-01 04:34:39 -0700143/* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
John Stultzea7cf492011-11-14 13:18:07 -0800144extern u64 ntp_tick_length(void);
Paul Mackerras726c14b2006-02-17 10:30:23 +1100145
John Stultz6b43ae82012-03-15 13:04:03 -0700146extern int second_overflow(unsigned long secs);
Stephen Rothwell3158e942006-03-26 01:37:29 -0800147extern int do_adjtimex(struct timex *);
Alexander Gordeev025b40a2011-01-12 17:00:56 -0800148extern void hardpps(const struct timespec *, const struct timespec *);
Stephen Rothwell3158e942006-03-26 01:37:29 -0800149
Andrew Morton941e4922008-02-06 01:36:42 -0800150int read_current_timer(unsigned long *timer_val);
151
Arnd Bergmann08604bd2009-06-16 15:31:12 -0700152/* The clock frequency of the i8253/i8254 PIT */
153#define PIT_TICK_RATE 1193182ul
154
Linus Torvalds1da177e2005-04-16 15:20:36 -0700155#endif /* LINUX_TIMEX_H */