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6588 serge 1 
/*****************************************************************************
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 *                                                                           *
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 * Copyright (c) David L. Mills 1993                                         *
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 *                                                                           *
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 * Permission to use, copy, modify, and distribute this software and its     *
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 * documentation for any purpose and without fee is hereby granted, provided *
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 * that the above copyright notice appears in all copies and that both the   *
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 * copyright notice and this permission notice appear in supporting          *
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 * documentation, and that the name University of Delaware not be used in    *
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 * advertising or publicity pertaining to distribution of the software       *
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 * without specific, written prior permission.  The University of Delaware   *
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 * makes no representations about the suitability this software for any      *
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 * purpose.  It is provided "as is" without express or implied warranty.     *
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 *                                                                           *
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 *****************************************************************************/
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/*
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 * Modification history timex.h
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 *
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 * 29 Dec 97	Russell King
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 *	Moved CLOCK_TICK_RATE, CLOCK_TICK_FACTOR and FINETUNE to asm/timex.h
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 *	for ARM machines
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 *
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 *  9 Jan 97    Adrian Sun
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 *      Shifted LATCH define to allow access to alpha machines.
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 *
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 * 26 Sep 94	David L. Mills
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 *	Added defines for hybrid phase/frequency-lock loop.
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 *
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 * 19 Mar 94	David L. Mills
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 *	Moved defines from kernel routines to header file and added new
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 *	defines for PPS phase-lock loop.
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 *
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 * 20 Feb 94	David L. Mills
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 *	Revised status codes and structures for external clock and PPS
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 *	signal discipline.
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 *
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 * 28 Nov 93	David L. Mills
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 *	Adjusted parameters to improve stability and increase poll
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 *	interval.
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 *
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 * 17 Sep 93    David L. Mills
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 *      Created file $NTP/include/sys/timex.h
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 * 07 Oct 93    Torsten Duwe
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 *      Derived linux/timex.h
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 * 1995-08-13    Torsten Duwe
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 *      kernel PLL updated to 1994-12-13 specs (rfc-1589)
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 * 1997-08-30    Ulrich Windl
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 *      Added new constant NTP_PHASE_LIMIT
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 * 2004-08-12    Christoph Lameter
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 *      Reworked time interpolation logic
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 */
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#ifndef _LINUX_TIMEX_H
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#define _LINUX_TIMEX_H
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#define ADJ_ADJTIME		0x8000	/* switch between adjtime/adjtimex modes */
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#define ADJ_OFFSET_SINGLESHOT	0x0001	/* old-fashioned adjtime */
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#define ADJ_OFFSET_READONLY	0x2000	/* read-only adjtime */
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#include
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#include
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#ifndef random_get_entropy
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/*
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 * The random_get_entropy() function is used by the /dev/random driver
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 * in order to extract entropy via the relative unpredictability of
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 * when an interrupt takes places versus a high speed, fine-grained
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 * timing source or cycle counter.  Since it will be occurred on every
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 * single interrupt, it must have a very low cost/overhead.
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 *
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 * By default we use get_cycles() for this purpose, but individual
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 * architectures may override this in their asm/timex.h header file.
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 */
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#define random_get_entropy()	get_cycles()
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#endif
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/*
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 * SHIFT_PLL is used as a dampening factor to define how much we
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 * adjust the frequency correction for a given offset in PLL mode.
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 * It also used in dampening the offset correction, to define how
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 * much of the current value in time_offset we correct for each
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 * second. Changing this value changes the stiffness of the ntp
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 * adjustment code. A lower value makes it more flexible, reducing
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 * NTP convergence time. A higher value makes it stiffer, increasing
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 * convergence time, but making the clock more stable.
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 *
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 * In David Mills' nanokernel reference implementation SHIFT_PLL is 4.
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 * However this seems to increase convergence time much too long.
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 *
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 * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html
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 *
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 * In the above mailing list discussion, it seems the value of 4
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 * was appropriate for other Unix systems with HZ=100, and that
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 * SHIFT_PLL should be decreased as HZ increases. However, Linux's
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 * clock steering implementation is HZ independent.
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 *
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 * Through experimentation, a SHIFT_PLL value of 2 was found to allow
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 * for fast convergence (very similar to the NTPv3 code used prior to
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 * v2.6.19), with good clock stability.
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 *
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 *
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 * SHIFT_FLL is used as a dampening factor to define how much we
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 * adjust the frequency correction for a given offset in FLL mode.
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 * In David Mills' nanokernel reference implementation SHIFT_FLL is 2.
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 *
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 * MAXTC establishes the maximum time constant of the PLL.
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 */
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#define SHIFT_PLL	2	/* PLL frequency factor (shift) */
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#define SHIFT_FLL	2	/* FLL frequency factor (shift) */
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#define MAXTC		10	/* maximum time constant (shift) */
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/*
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 * SHIFT_USEC defines the scaling (shift) of the time_freq and
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 * time_tolerance variables, which represent the current frequency
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 * offset and maximum frequency tolerance.
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 */
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#define SHIFT_USEC 16		/* frequency offset scale (shift) */
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#define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC))
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#define PPM_SCALE_INV_SHIFT 19
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#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \
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		       PPM_SCALE + 1)
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#define MAXPHASE 500000000L	/* max phase error (ns) */
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#define MAXFREQ 500000		/* max frequency error (ns/s) */
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#define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT)
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#define MINSEC 256		/* min interval between updates (s) */
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#define MAXSEC 2048		/* max interval between updates (s) */
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#define NTP_PHASE_LIMIT ((MAXPHASE / NSEC_PER_USEC) << 5) /* beyond max. dispersion */
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/*
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 * kernel variables
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 * Note: maximum error = NTP synch distance = dispersion + delay / 2;
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 * estimated error = NTP dispersion.
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 */
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extern unsigned long tick_usec;		/* USER_HZ period (usec) */
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extern unsigned long tick_nsec;		/* SHIFTED_HZ period (nsec) */
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/* Required to safely shift negative values */
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#define shift_right(x, s) ({	\
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	__typeof__(x) __x = (x);	\
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	__typeof__(s) __s = (s);	\
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	__x < 0 ? -(-__x >> __s) : __x >> __s;	\
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})
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#define NTP_SCALE_SHIFT		32
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#define NTP_INTERVAL_FREQ  (HZ)
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#define NTP_INTERVAL_LENGTH (NSEC_PER_SEC/NTP_INTERVAL_FREQ)
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int read_current_timer(unsigned long *timer_val);
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void ntp_notify_cmos_timer(void);
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/* The clock frequency of the i8253/i8254 PIT */
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#define PIT_TICK_RATE 1193182ul
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#endif /* LINUX_TIMEX_H */