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 | #include <asm/timex.h> |
66 | |
67 | #ifndef random_get_entropy |
68 | /* |
69 | * The random_get_entropy() function is used by the /dev/random driver |
70 | * in order to extract entropy via the relative unpredictability of |
71 | * when an interrupt takes places versus a high speed, fine-grained |
72 | * timing source or cycle counter. Since it will be occurred on every |
73 | * single interrupt, it must have a very low cost/overhead. |
74 | * |
75 | * By default we use get_cycles() for this purpose, but individual |
76 | * architectures may override this in their asm/timex.h header file. |
77 | */ |
78 | #define random_get_entropy() get_cycles() |
79 | #endif |
80 | |
81 | /* |
82 | * SHIFT_PLL is used as a dampening factor to define how much we |
83 | * adjust the frequency correction for a given offset in PLL mode. |
84 | * It also used in dampening the offset correction, to define how |
85 | * much of the current value in time_offset we correct for each |
86 | * second. Changing this value changes the stiffness of the ntp |
87 | * adjustment code. A lower value makes it more flexible, reducing |
88 | * NTP convergence time. A higher value makes it stiffer, increasing |
89 | * convergence time, but making the clock more stable. |
90 | * |
91 | * In David Mills' nanokernel reference implementation SHIFT_PLL is 4. |
92 | * However this seems to increase convergence time much too long. |
93 | * |
94 | * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html |
95 | * |
96 | * In the above mailing list discussion, it seems the value of 4 |
97 | * was appropriate for other Unix systems with HZ=100, and that |
98 | * SHIFT_PLL should be decreased as HZ increases. However, Linux's |
99 | * clock steering implementation is HZ independent. |
100 | * |
101 | * Through experimentation, a SHIFT_PLL value of 2 was found to allow |
102 | * for fast convergence (very similar to the NTPv3 code used prior to |
103 | * v2.6.19), with good clock stability. |
104 | * |
105 | * |
106 | * SHIFT_FLL is used as a dampening factor to define how much we |
107 | * adjust the frequency correction for a given offset in FLL mode. |
108 | * In David Mills' nanokernel reference implementation SHIFT_FLL is 2. |
109 | * |
110 | * MAXTC establishes the maximum time constant of the PLL. |
111 | */ |
112 | #define SHIFT_PLL 2 /* PLL frequency factor (shift) */ |
113 | #define SHIFT_FLL 2 /* FLL frequency factor (shift) */ |
114 | #define MAXTC 10 /* maximum time constant (shift) */ |
115 | |
116 | /* |
117 | * SHIFT_USEC defines the scaling (shift) of the time_freq and |
118 | * time_tolerance variables, which represent the current frequency |
119 | * offset and maximum frequency tolerance. |
120 | */ |
121 | #define SHIFT_USEC 16 /* frequency offset scale (shift) */ |
122 | #define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC)) |
123 | #define PPM_SCALE_INV_SHIFT 19 |
124 | #define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \ |
125 | PPM_SCALE + 1) |
126 | |
127 | #define MAXPHASE 500000000L /* max phase error (ns) */ |
128 | #define MAXFREQ 500000 /* max frequency error (ns/s) */ |
129 | #define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT) |
130 | #define MINSEC 256 /* min interval between updates (s) */ |
131 | #define MAXSEC 2048 /* max interval between updates (s) */ |
132 | #define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */ |
133 | |
134 | /* |
135 | * kernel variables |
136 | * Note: maximum error = NTP synch distance = dispersion + delay / 2; |
137 | * estimated error = NTP dispersion. |
138 | */ |
139 | extern unsigned long tick_usec; /* USER_HZ period (usec) */ |
140 | extern unsigned long tick_nsec; /* SHIFTED_HZ period (nsec) */ |
141 | |
142 | /* Required to safely shift negative values */ |
143 | #define shift_right(x, s) ({ \ |
144 | __typeof__(x) __x = (x); \ |
145 | __typeof__(s) __s = (s); \ |
146 | __x < 0 ? -(-__x >> __s) : __x >> __s; \ |
147 | }) |
148 | |
149 | #define NTP_SCALE_SHIFT 32 |
150 | |
151 | #define NTP_INTERVAL_FREQ (HZ) |
152 | #define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ) |
153 | |
154 | extern int do_adjtimex(struct __kernel_timex *); |
155 | extern int do_clock_adjtime(const clockid_t which_clock, struct __kernel_timex * ktx); |
156 | |
157 | extern void hardpps(const struct timespec64 *, const struct timespec64 *); |
158 | |
159 | int read_current_timer(unsigned long *timer_val); |
160 | void ntp_notify_cmos_timer(void); |
161 | |
162 | /* The clock frequency of the i8253/i8254 PIT */ |
163 | #define PIT_TICK_RATE 1193182ul |
164 | |
165 | #endif /* LINUX_TIMEX_H */ |
166 | |