--- /dev/null
+/*****************************************************************************
+ * *
+ * 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 */
Code Review / kvmfornfv.git / blobdiff