cregit-Linux how code gets into the kernel

Release 4.7 include/linux/timex.h

Directory: include/linux
/*****************************************************************************
 *                                                                           *
 * 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>

#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.
 */

#define random_get_entropy()	get_cycles()
#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 synch 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 timex *);
extern void hardpps(const struct timespec64 *, const struct timespec64 *);

int read_current_timer(unsigned long *timer_val);
void ntp_notify_cmos_timer(void);

/* The clock frequency of the i8253/i8254 PIT */

#define PIT_TICK_RATE 1193182ul

#endif /* LINUX_TIMEX_H */

Overall Contributors

PersonTokensPropCommitsCommitProp
mike frysingermike frysinger6734.54%13.85%
john stultzjohn stultz2914.95%726.92%
roman zippelroman zippel2010.31%415.38%
pre-gitpre-git168.25%311.54%
alexander gordeevalexander gordeev136.70%13.85%
theodore tsotheodore tso115.67%13.85%
andrew mortonandrew morton94.64%13.85%
rolf fokkensrolf fokkens84.12%13.85%
stephen rothwellstephen rothwell84.12%13.85%
arnd bergmannarnd bergmann73.61%27.69%
david woodhousedavid woodhouse31.55%13.85%
christoph lameterchristoph lameter10.52%13.85%
david howellsdavid howells10.52%13.85%
ingo molnaringo molnar10.52%13.85%
Total194100.00%26100.00%
Directory: include/linux
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