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Diffstat (limited to 'include/linux/timex.h')
| -rw-r--r-- | include/linux/timex.h | 172 |
1 files changed, 172 insertions, 0 deletions
diff --git a/include/linux/timex.h b/include/linux/timex.h new file mode 100644 index 000000000..3871b06bd --- /dev/null +++ b/include/linux/timex.h @@ -0,0 +1,172 @@ +/***************************************************************************** + * * + * 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 */ |