/***************************************************************************** * * * Copyright (c) David L. Mills 1993 * * * * Permission to use, copy, modify, and distribute this software and its * * documentation for any purpose and without fee is hereby granted, provided * * that the above copyright notice appears in all copies and that both the * * copyright notice and this permission notice appear in supporting * * documentation, and that the name University of Delaware not be used in * * advertising or publicity pertaining to distribution of the software * * without specific, written prior permission. The University of Delaware * * makes no representations about the suitability this software for any * * purpose. It is provided "as is" without express or implied warranty. * * * *****************************************************************************/ /* * Modification history timex.h * * 29 Dec 97 Russell King * Moved CLOCK_TICK_RATE, CLOCK_TICK_FACTOR and FINETUNE to asm/timex.h * for ARM machines * * 9 Jan 97 Adrian Sun * Shifted LATCH define to allow access to alpha machines. * * 26 Sep 94 David L. Mills * Added defines for hybrid phase/frequency-lock loop. * * 19 Mar 94 David L. Mills * Moved defines from kernel routines to header file and added new * defines for PPS phase-lock loop. * * 20 Feb 94 David L. Mills * Revised status codes and structures for external clock and PPS * signal discipline. * * 28 Nov 93 David L. Mills * Adjusted parameters to improve stability and increase poll * interval. * * 17 Sep 93 David L. Mills * Created file $NTP/include/sys/timex.h * 07 Oct 93 Torsten Duwe * Derived linux/timex.h * 1995-08-13 Torsten Duwe * kernel PLL updated to 1994-12-13 specs (rfc-1589) * 1997-08-30 Ulrich Windl * Added new constant NTP_PHASE_LIMIT * 2004-08-12 Christoph Lameter * Reworked time interpolation logic */ #ifndef _LINUX_TIMEX_H #define _LINUX_TIMEX_H #include <uapi/linux/timex.h> #define ADJ_ADJTIME … #define ADJ_OFFSET_SINGLESHOT … #define ADJ_OFFSET_READONLY … #include <linux/compiler.h> #include <linux/types.h> #include <linux/param.h> unsigned long random_get_entropy_fallback(void); #include <asm/timex.h> #ifndef random_get_entropy /* * The random_get_entropy() function is used by the /dev/random driver * in order to extract entropy via the relative unpredictability of * when an interrupt takes places versus a high speed, fine-grained * timing source or cycle counter. Since it will be occurred on every * single interrupt, it must have a very low cost/overhead. * * By default we use get_cycles() for this purpose, but individual * architectures may override this in their asm/timex.h header file. * If a given arch does not have get_cycles(), then we fallback to * using random_get_entropy_fallback(). */ #ifdef get_cycles #define random_get_entropy … #else #define random_get_entropy … #endif #endif /* * SHIFT_PLL is used as a dampening factor to define how much we * adjust the frequency correction for a given offset in PLL mode. * It also used in dampening the offset correction, to define how * much of the current value in time_offset we correct for each * second. Changing this value changes the stiffness of the ntp * adjustment code. A lower value makes it more flexible, reducing * NTP convergence time. A higher value makes it stiffer, increasing * convergence time, but making the clock more stable. * * In David Mills' nanokernel reference implementation SHIFT_PLL is 4. * However this seems to increase convergence time much too long. * * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html * * In the above mailing list discussion, it seems the value of 4 * was appropriate for other Unix systems with HZ=100, and that * SHIFT_PLL should be decreased as HZ increases. However, Linux's * clock steering implementation is HZ independent. * * Through experimentation, a SHIFT_PLL value of 2 was found to allow * for fast convergence (very similar to the NTPv3 code used prior to * v2.6.19), with good clock stability. * * * SHIFT_FLL is used as a dampening factor to define how much we * adjust the frequency correction for a given offset in FLL mode. * In David Mills' nanokernel reference implementation SHIFT_FLL is 2. * * MAXTC establishes the maximum time constant of the PLL. */ #define SHIFT_PLL … #define SHIFT_FLL … #define MAXTC … /* * SHIFT_USEC defines the scaling (shift) of the time_freq and * time_tolerance variables, which represent the current frequency * offset and maximum frequency tolerance. */ #define SHIFT_USEC … #define PPM_SCALE … #define PPM_SCALE_INV_SHIFT … #define PPM_SCALE_INV … #define MAXPHASE … #define MAXFREQ … #define MAXFREQ_SCALED … #define MINSEC … #define MAXSEC … #define NTP_PHASE_LIMIT … /* * kernel variables * Note: maximum error = NTP sync distance = dispersion + delay / 2; * estimated error = NTP dispersion. */ extern unsigned long tick_usec; /* USER_HZ period (usec) */ extern unsigned long tick_nsec; /* SHIFTED_HZ period (nsec) */ /* Required to safely shift negative values */ #define shift_right(x, s) … #define NTP_SCALE_SHIFT … #define NTP_INTERVAL_FREQ … #define NTP_INTERVAL_LENGTH … extern int do_adjtimex(struct __kernel_timex *); extern int do_clock_adjtime(const clockid_t which_clock, struct __kernel_timex * ktx); extern void hardpps(const struct timespec64 *, const struct timespec64 *); int read_current_timer(unsigned long *timer_val); /* The clock frequency of the i8253/i8254 PIT */ #define PIT_TICK_RATE … #endif /* LINUX_TIMEX_H */
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