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 timex *); 155 extern void hardpps(const struct timespec64 *, const struct timespec64 *); 156 157 int read_current_timer(unsigned long *timer_val); 158 void ntp_notify_cmos_timer(void); 159 160 /* The clock frequency of the i8253/i8254 PIT */ 161 #define PIT_TICK_RATE 1193182ul 162 163 #endif /* LINUX_TIMEX_H */ 164
