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 unsigned 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 */
147 extern unsigned long tick_usec; /* USER_HZ period (usec) */
148 extern 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
162 extern int do_adjtimex(struct __kernel_timex *);
163 extern int do_clock_adjtime(const clockid_t which_clock, struct __kernel_timex * ktx);
164
165 extern void hardpps(const struct timespec64 *, const struct timespec64 *);
166
167 int 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
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