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  /*****************************************************************************
   *                                                                           *
   * 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 timespec *, const struct timespec *);
  
  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 */