xref: /openbmc/linux/include/linux/timex.h (revision 82f18281)
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