1 /*****************************************************************************
3 * Copyright (c) David L. Mills 1993 *
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. *
15 *****************************************************************************/
18 * Modification history timex.h
20 * 29 Dec 97 Russell King
21 * Moved CLOCK_TICK_RATE, CLOCK_TICK_FACTOR and FINETUNE to asm/timex.h
25 * Shifted LATCH define to allow access to alpha machines.
27 * 26 Sep 94 David L. Mills
28 * Added defines for hybrid phase/frequency-lock loop.
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.
34 * 20 Feb 94 David L. Mills
35 * Revised status codes and structures for external clock and PPS
38 * 28 Nov 93 David L. Mills
39 * Adjusted parameters to improve stability and increase poll
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
53 #ifndef _LINUX_TIMEX_H
54 #define _LINUX_TIMEX_H
56 #include <uapi/linux/timex.h>
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>
65 #include <asm/timex.h>
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.
77 * In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
78 * However this seems to increase convergence time much too long.
80 * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html
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.
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.
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.
96 * MAXTC establishes the maximum time constant of the PLL.
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) */
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.
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)) / \
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 */
122 * Note: maximum error = NTP synch distance = dispersion + delay / 2;
123 * estimated error = NTP dispersion.
125 extern unsigned long tick_usec
; /* USER_HZ period (usec) */
126 extern unsigned long tick_nsec
; /* SHIFTED_HZ period (nsec) */
128 extern void ntp_init(void);
129 extern void ntp_clear(void);
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; \
138 #define NTP_SCALE_SHIFT 32
140 #define NTP_INTERVAL_FREQ (HZ)
141 #define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
143 /* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
144 extern u64
ntp_tick_length(void);
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
*);
150 int read_current_timer(unsigned long *timer_val
);
152 /* The clock frequency of the i8253/i8254 PIT */
153 #define PIT_TICK_RATE 1193182ul
155 #endif /* LINUX_TIMEX_H */
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