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