Current File : //usr/src/linux-headers-5.15.0-125-generic/include/linux/timex.h
/*****************************************************************************
* *
* 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 0x8000 /* switch between adjtime/adjtimex modes */
#define ADJ_OFFSET_SINGLESHOT 0x0001 /* old-fashioned adjtime */
#define ADJ_OFFSET_READONLY 0x2000 /* read-only adjtime */
#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() ((unsigned long)get_cycles())
#else
#define random_get_entropy() random_get_entropy_fallback()
#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 2 /* PLL frequency factor (shift) */
#define SHIFT_FLL 2 /* FLL frequency factor (shift) */
#define MAXTC 10 /* maximum time constant (shift) */
/*
* 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 16 /* frequency offset scale (shift) */
#define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
#define PPM_SCALE_INV_SHIFT 19
#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
PPM_SCALE + 1)
#define MAXPHASE 500000000L /* max phase error (ns) */
#define MAXFREQ 500000 /* max frequency error (ns/s) */
#define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT)
#define MINSEC 256 /* min interval between updates (s) */
#define MAXSEC 2048 /* max interval between updates (s) */
#define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */
/*
* 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) ({ \
__typeof__(x) __x = (x); \
__typeof__(s) __s = (s); \
__x < 0 ? -(-__x >> __s) : __x >> __s; \
})
#define NTP_SCALE_SHIFT 32
#define NTP_INTERVAL_FREQ (HZ)
#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
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 1193182ul
#endif /* LINUX_TIMEX_H */
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