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/* 68 * SHIFT_PLL is used as a dampening factor to define how much we 69 * adjust the frequency correction for a given offset in PLL mode. 70 * It also used in dampening the offset correction, to define how 71 * much of the current value in time_offset we correct for each 72 * second. Changing this value changes the stiffness of the ntp 73 * adjustment code. A lower value makes it more flexible, reducing 74 * NTP convergence time. A higher value makes it stiffer, increasing 75 * convergence time, but making the clock more stable. 76 * 77 * In David Mills' nanokernel reference implementation SHIFT_PLL is 4. 78 * However this seems to increase convergence time much too long. 79 * 80 * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html 81 * 82 * In the above mailing list discussion, it seems the value of 4 83 * was appropriate for other Unix systems with HZ=100, and that 84 * SHIFT_PLL should be decreased as HZ increases. However, Linux's 85 * clock steering implementation is HZ independent. 86 * 87 * Through experimentation, a SHIFT_PLL value of 2 was found to allow 88 * for fast convergence (very similar to the NTPv3 code used prior to 89 * v2.6.19), with good clock stability. 90 * 91 * 92 * SHIFT_FLL is used as a dampening factor to define how much we 93 * adjust the frequency correction for a given offset in FLL mode. 94 * In David Mills' nanokernel reference implementation SHIFT_FLL is 2. 95 * 96 * MAXTC establishes the maximum time constant of the PLL. 97 */ 98#define SHIFT_PLL 2 /* PLL frequency factor (shift) */ 99#define SHIFT_FLL 2 /* FLL frequency factor (shift) */ 100#define MAXTC 10 /* maximum time constant (shift) */ 101 102/* 103 * SHIFT_USEC defines the scaling (shift) of the time_freq and 104 * time_tolerance variables, which represent the current frequency 105 * offset and maximum frequency tolerance. 106 */ 107#define SHIFT_USEC 16 /* frequency offset scale (shift) */ 108#define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC)) 109#define PPM_SCALE_INV_SHIFT 19 110#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \ 111 PPM_SCALE + 1) 112 113#define MAXPHASE 500000000L /* max phase error (ns) */ 114#define MAXFREQ 500000 /* max frequency error (ns/s) */ 115#define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT) 116#define MINSEC 256 /* min interval between updates (s) */ 117#define MAXSEC 2048 /* max interval between updates (s) */ 118#define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */ 119 120/* 121 * kernel variables 122 * Note: maximum error = NTP synch distance = dispersion + delay / 2; 123 * estimated error = NTP dispersion. 124 */ 125extern unsigned long tick_usec; /* USER_HZ period (usec) */ 126extern unsigned long tick_nsec; /* SHIFTED_HZ period (nsec) */ 127 128/* Required to safely shift negative values */ 129#define shift_right(x, s) ({ \ 130 __typeof__(x) __x = (x); \ 131 __typeof__(s) __s = (s); \ 132 __x < 0 ? -(-__x >> __s) : __x >> __s; \ 133}) 134 135#define NTP_SCALE_SHIFT 32 136 137#define NTP_INTERVAL_FREQ (HZ) 138#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ) 139 140extern int do_adjtimex(struct timex *); 141extern void hardpps(const struct timespec *, const struct timespec *); 142 143int read_current_timer(unsigned long *timer_val); 144 145/* The clock frequency of the i8253/i8254 PIT */ 146#define PIT_TICK_RATE 1193182ul 147 148#endif /* LINUX_TIMEX_H */ 149