include/linux/timex.h - linux-imx - Git at Google

 /*****************************************************************************
  *                                                                           *
  * 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>

 /*
  * 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) */

 extern void ntp_init(void);
 extern void ntp_clear(void);

 /* 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)

 /* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
 extern u64 ntp_tick_length(void);

 extern int second_overflow(unsigned long secs);
 extern int do_adjtimex(struct timex *);
 extern void hardpps(const struct timespec *, const struct timespec *);

 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 */
	/*****************************************************************************
	* *
	* 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>

	/*
	* 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) */

	extern void ntp_init(void);
	extern void ntp_clear(void);

	/* 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)

	/* Returns how long ticks are at present, in ns / 2^NTP_SCALE_SHIFT. */
	extern u64 ntp_tick_length(void);

	extern int second_overflow(unsigned long secs);
	extern int do_adjtimex(struct timex *);
	extern void hardpps(const struct timespec , const struct timespec );

	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 */