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